Bihar Board 10th Objective Questions and Answers

Bihar Board 10th Matric Science Objective Questions and Answers Key 2020-2021 Pdf Download

Bihar Board 10th Science Objective Questions and Answers in Hindi

Bihar Board 10th Chemistry Objective Answers in Hindi

• Chapter 1 रासायनिक अभिक्रियाएँ एवं समीकरण
• Chapter 2 अम्ल, क्षारक एवं लवण
• Chapter 3 धातु एवं अधातु
• Chapter 4 कार्बन एवं इसके यौगिक
• Chapter 5 तत्वों का आवर्त वर्गीकरण

Bihar Board 10th Biology Objective Answers in Hindi

• Chapter 6 जैव प्रक्रम
• Chapter 7 नियंत्रण एवं समन्वय
• Chapter 8 जीव जनन कैसे करते है
• Chapter 9 अनुवांशिकता एवं जैव विकास
• Chapter 14 उर्जा के स्रोत
• Chapter 15 हमारा पर्यावरण
• Chapter 16 प्राकृतिक संसाधनों का संपोषित प्रबंधन

Bihar Board 10th Physics Objective Answers in Hindi

• Chapter 10 प्रकाश-परावर्तन तथा अपवर्तन
• Chapter 11 मानव नेत्र एवं रंगबिरंगा संसार
• Chapter 12 विद्युत
• Chapter 13 विद्युत धारा का चुम्बकीय प्रभाव

Bihar Board 10th Science VVI Objective Model Set Questions

• Bihar Board 10th Science Objective Model Set 1
• Bihar Board 10th Science Objective Model Set 2
• Bihar Board 10th Science Objective Model Set 3
• Bihar Board 10th Science Objective Model Set 4
• Bihar Board 10th Science Objective Model Set 5
• Bihar Board 10th Science Objective Model Set 6
• Bihar Board 10th Science Objective Model Set 7

Bihar Board 10th Science Objective Questions and Answers in English

• Chapter 1 Chemical Reactions and Equations
• Chapter 2 Acids, Bases and Salts
• Chapter 3 Metals and Non-metals
• Chapter 4 Carbon and Its Compounds
• Chapter 5 Periodic Classification of Elements
• Chapter 6 Life Processes
• Chapter 7 Control and Coordination
• Chapter 8 How do Organisms Reproduce?
• Chapter 9 Heredity and Evolution
• Chapter 10 Light Reflection and Refraction
• Chapter 11 Human Eye and Colourful World
• Chapter 12 Electricity
• Chapter 13 Magnetic Effects of Electric Current
• Chapter 14 Sources of Energy
• Chapter 15 Our Environment
• Chapter 16 Management of Natural Resources

Bihar Board 10th Matric Objective Questions and Answers Key 2020-2021 Pdf Download

Bihar Board 10th Objective Questions and Answers Key

• Bihar Board 10th Maths Objective Questions and Answers
• Bihar Board 10th Science Objective Questions and Answers
• Bihar Board 10th Social Science Objective Questions and Answers
• Bihar Board 10th English Objective Questions and Answers
• Bihar Board 10th Hindi Objective Questions and Answers
• Bihar Board 10th Sanskrit Objective Questions and Answers

Bihar Board 10th Objective Questions and Answers

Bihar Board 10th Matric Maths Objective Questions and Answers Key Pdf Download

Bihar Board 10th Maths Objective Questions and Answers in Hindi

• Chapter 1 वास्तविक संख्याएँ
• Chapter 2 बहुपद
• Chapter 3 दो चरों वाले रखिक समीकरण का युग्म
• Chapter 4 द्विघात समीकरण
• Chapter 5 समांतर श्रेढ़ियाँ
• Chapter 6 त्रिभुज
• Chapter 7 निर्देशांक ज्यामिति
• Chapter 8 त्रिकोणमिति का परिचय
• Chapter 9 त्रिकोणमिति का अनुप्रयोग
• Chapter 10 वृत्त
• Chapter 11 रचनाएँ
• Chapter 12 वृतों से संबंधित क्षेत्रफल
• Chapter 13 पृष्ठीय क्षेत्रफल एवं आयतन
• Chapter 14 सांख्यिकी
• Chapter 15 प्रायिकता
• Bihar Board 10th Maths Objective Model Set 1
• Bihar Board 10th Maths Objective Model Set 2
• Bihar Board 10th Maths Objective Model Set 3
• Bihar Board 10th Maths Objective Model Set 4
• Bihar Board 10th Maths Objective Model Set 5

Bihar Board 10th Maths Objective Questions and Answers in English

• Chapter 1 Real Numbers
• Chapter 2 Polynomials
• Chapter 3 Pair of Linear Equations in Two Variables
• Chapter 4 Quadratic Equations
• Chapter 5 Arithmetic Progressions
• Chapter 6 Triangles
• Chapter 7 Coordinate Geometry
• Chapter 8 Introduction to Trigonometry
• Chapter 9 Some Applications of Trigonometry
• Chapter 10 Circles
• Chapter 11 Constructions
• Chapter 12 Areas Related to Circles
• Chapter 13 Surface Areas and Volumes
• Chapter 14 Statistics
• Chapter 15 Probability

Bihar Board 10th Objective Questions and Answers

Bihar Board 10th Matric Social Science Objective Questions and Answers Key 2020-2021 Pdf Download

Bihar Board 10th Social Science Objective Questions and Answers in Hindi

Bihar Board Class 10th History Objective Answers

इतिहास : इतिहास की दुनिया भाग 2

• Chapter 1 यूरोप में राष्ट्रवाद
• Chapter 2 समाजवाद एवं साम्यवाद
• Chapter 3 हिन्द-चीन में राष्ट्रवादी आंदोलन
• Chapter 4 भारत में राष्ट्रवाद
• Chapter 5 अर्थव्यवस्था और आजीविका
• Chapter 6 शहरीकरण एवं शहरी जीवन
• Chapter 7 व्यापार और भूमंडलीकरण
• Chapter 8 प्रेस एवं सस्कृतिक राष्ट्रवाद

Bihar Board Class 10th Geography Objective Answers

भूगोल : भारत : भूमि एवं लोग भाग 2

• Chapter 1 भारत : संसाधन एवं उपयोग
• Chapter 2 भूमि और मृदा संसाधन
• Chapter 3 जल संसाधन
• Chapter 4 वन और वन्य प्राणी संसाधन
• Chapter 5 खनिज संसाधन
• Chapter 6 शक्ति (ऊर्जा) संसाधन
• Chapter 7 कृषि संसाधन
• Chapter 8 निर्माण उद्योग
• Chapter 9 परिवहन, संचार एवं व्यापार
• Chapter 10 बिहार : संसाधन एवं उपयोग
• Chapter 11 मानचित्र अध्ययन (उच्चावच निरूपण)

Bihar Board Class 10th Political Science Objective Answers

राजनीति विज्ञान : लोकतांत्रिक राजनीति भाग 2

• Chapter 1 लोकतंत्र में सत्ता की साझेदारी
• Chapter 2 सत्ता में साझेदारी की कार्यप्रणाली
• Chapter 3 लोकतंत्र में प्रतिस्पर्धा एवं संघर्ष
• Chapter 4 लोकतंत्र की उपलब्धियाँ
• Chapter 5 लोकतंत्र की चुनौतियाँ

Bihar Board Class 10th Economics Objective Answers

अर्थशास्त्र : हमारी अर्थव्यवस्था भाग 2

• Chapter 1 अर्थव्यवस्था एवं इसके विकास का इतिहास
• Chapter 2 राज्य एवं राष्ट्र की आय
• Chapter 3 मुद्रा, बचत एवं साख
• Chapter 4 हमारी वित्तीय संस्थाएँ
• Chapter 5 रोजगार एवं सेवाएँ
• Chapter 6 वैश्वीकरण
• Chapter 7 उपभोक्ता जागरण एवं संरक्षण

Bihar Board Class 10th Disaster Management Objective Answers

आपदा प्रबन्धन

• Chapter 1 प्राकृतिक आपदा : एक परिचय
• Chapter 2 प्राकृतिक आपदा एवं प्रबंधन : बाढ़ सुखाड़
• Chapter 3 प्राकृतिक आपदा एवं प्रबंधन : भूकंप एवं सुनामी
• Chapter 4 जीवन रक्षक आकस्मिक प्रबंधन
• Chapter 5 आपदा काल में वैकल्पिक संचार व्यवस्था
• Chapter 6 आपदा और सह अस्तित्व

Bihar Board Class 10th Objective Objective Model Sets

• Bihar Board 10th Social Science Objective Model Set 1
• Bihar Board 10th Social Science Objective Model Set 2
• Bihar Board 10th Social Science Objective Model Set 3
• Bihar Board 10th Social Science Objective Model Set 4
• Bihar Board 10th Social Science Objective Model Set 5
• Bihar Board 10th Social Science Objective Model Set 6
• Bihar Board 10th Social Science Objective Model Set 7

Here we have updated the detailed SCERT Bihar Board 10th Class Science Book Solutions Vigyan of BTBC Book Class 10 Science Solutions Answers Guide, Bihar Text Book Class 10 Science Questions and Answers, Chapter Wise Notes Pdf, Model Question Papers, Study Material to help students in understanding the concepts behind each question in a simpler and detailed way.

BSEB Bihar Board Class 10 Science Book Solution in Hindi & English Medium

Bihar Board Class 10 Science Solution in Hindi Medium

Bihar Board Class 10 Science Chemistry Solution in Hindi

• Chapter 1 रासायनिक अभिक्रियाएँ एवं समीकरण
• Chapter 2 अम्ल, क्षारक एवं लवण
• Chapter 3 धातु एवं अधातु
• Chapter 4 कार्बन एवं इसके यौगिक
• Chapter 5 तत्वों का आवर्त वर्गीकरण

Bihar Board Class 10 Science Biology Solution in Hindi

• Chapter 6 जैव प्रक्रम
• Chapter 7 नियंत्रण एवं समन्वय
• Chapter 8 जीव जनन कैसे करते है
• Chapter 9 अनुवांशिकता एवं जैव विकास
• Chapter 14 उर्जा के स्रोत
• Chapter 15 हमारा पर्यावरण
• Chapter 16 प्राकृतिक संसाधनों का संपोषित प्रबंधन

Bihar Board Class 10 Science Physics Solution in Hindi

• Chapter 10 प्रकाश-परावर्तन तथा अपवर्तन
• Chapter 11 मानव नेत्र एवं रंगबिरंगा संसार
• Chapter 12 विद्युत
• Chapter 13 विद्युत धारा का चुम्बकीय प्रभाव

Bihar Board Class 10 Science Solution in English Medium

Bihar Board Class 10 Science Chemistry Solution

• Chapter 1 Chemical Reactions and Equations
• Chapter 2 Acids, Bases and Salts
• Chapter 3 Metals and Non-metals
• Chapter 4 Carbon and Its Compounds
• Chapter 5 Periodic Classification of Elements

Bihar Board Class 10 Science Biology Solution

• Chapter 6 Life Processes
• Chapter 7 Control and Coordination
• Chapter 8 How do Organisms Reproduce?
• Chapter 9 Heredity and Evolution
• Chapter 14 Sources of Energy
• Chapter 15 Our Environment
• Chapter 16 Management of Natural Resources

Bihar Board Class 10 Science Physics Solution

• Chapter 10 Light Reflection and Refraction
• Chapter 11 Human Eye and Colourful World
• Chapter 12 Electricity
• Chapter 13 Magnetic Effects of Electric Current

We hope that BSTBPC BSEB Bihar Board Class 10th Matric Science Book Solutions विज्ञान PDF Free Download in Hindi Medium and English Medium of BTBC Book Class 10 Science Solutions Answers Guide, Bihar Text Book Class 10 Science Questions and Answers, Chapter Wise Notes Pdf, Model Question Papers, Study Material will help students can prepare all the concepts covered in the syllabus.

If you face any issues concerning SCERT Bihar Board Class 10th Science Text Book Solutions Vigyan, you can ask in the comment section below, we will surely help you out.

Here we have updated the detailed SCERT Bihar Board 10th Class Maths Book Solutions Ganit of BTBC Book Class 10 Maths Solutions Answers Guide, Bihar Text Book Class 10 Maths Questions and Answers, Chapter Wise Notes Pdf, Model Question Papers, Study Material to help students in understanding the concepts behind each question in a simpler and detailed way.

Bihar Board Class 10 Science Solutions Chapter 12 Electricity

Bihar Board Class 10 Science Chapter 12 Electricity InText Questions and Answers

In-text Questions (Page 200)

Question 1.
What does an electric circuit mean?
Answer:
A continuous conducting path consisting of wires and other resistances (like electric bulb, etc.) and a switch, between the two terminals of a cell or battery, along which an electric current flows, is called a circuit.

Free Median Calculator – find the Median of a data set step-by-step.

Question 2.
Define the unit of current.
Answer:
The SI unit of electric current is ampere (which is denoted by the letter A). When 1 coulomb of charge flows through any cross-section of a conductor in 1 second, the current flowing through it is said to be 1 ampere.

Question 3.
Calculate the number of electrons constituting one coulomb of charge.
Answer:
The charge on an electron, e = 1.6 × 10^-19 c. No. of electrons constituting 1 coulomb is given by

In-text Questions (Page 202)

Question 1.
Name a device that helps to maintain a potential difference across a conductor.
Answer:
An electrical cell (or a battery).

Question 2.
What is mean by saying that the potential difference between two points is 1 V?
Answer:
The potential difference between two points is said to be 1 volt (1 V) if 1 joule of work is done in moving 1 coulomb of electric charge from one point to the other.

Question 3.
How much energy is given to each coulomb of charge passing through a 6 V battery?
Answer:
W = QV = 1C × 6V = 6J

In-text Questions (Page 209)

Question 1.
On what factors does the resistance of a conductor depend?
Answer:
The electrical resistance of a conductor (or a wire) depends on the following factors:

• length of the conductor,
• area of cross-section of the conductor (or thickness of the conductor),
• nature of the material of the conductor, and
• temperature of the conductor.

Question 2.
Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why?
Answer:
The current will flow more easily through a thick wire than through a thin wire of the same material when connected to the same source (like a battery). This is due to the fact that the resistance of a wire is inversely proportional to the square of its diameter. A thick wire has greater diameter and hence lesser resistance making the current to flow through it more easily. On the other hand, a thin wire has smaller diameter and hence greater resistance to the flow of current through it.

Question 3.
Let the resistance of an electrical component remain constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?
Answer:
The current through the component will also decrease to half of its former value.

Question 4.
Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?
Answer:
The coils (or heating elements) of toasters and electric irons are made of an alloy rather than a pure metal because:

• the resistivity of an alloy is much higher than that of a pure metal, and
• an alloy does not undergo oxidation (or burn) easily even at high temperature, when it is red hot.

Question 5.
Use the data in Table on page 207 of this book to answer the following:
(a) Which among iron and mercury is a better conductor?
(b) Which material is the best conductor?
Answer:
(a) The electrical resistivity of iron is 10.0 × 10^-8 Ω m whereas that of mercury is 94.0 × 10^-8 Ω m. Since the resistivity of iron is less than that of mercury, therefore, iron is a better conductor than mercury.
(b) Silver metal has the lowest electrical resistivity (1.60 × 10^-8 Ω m), therefore, silver metal is the best conductor of electricity.

In-text Questions (Page 213)

Question 1.
Draw a schematic diagram of a circuit consisting of a battery of three cells of 2 V each, a 5 Ω resistor, an 8 Ω resistor, and a 12 Ω, resistor, and a plug key, all connected in series.
Answer:
A schematic diagram of a circuit consisting of a battery of three 2V cells, a 5Ω resistor, an 8Ω resistor and a 12Ω resistor and a plug key, K; all connected in series, is shown in figure given below.

Question 2.
Redraw the circuit of Question 1 putting an ammeter to measure the current through the resistors and a voltmeter to measure the potential difference across the 12 Ω resistor. What would be the reading in the ammeter and the voltmeter?
Answer:
The circuit diagram of question 1 with an ammeter and voltmeter V across the 12 Ω resistor is shown in figure given below.

Since three resistance are in series.
Total resistance of circuit, R = 5Ω + 8Ω + 12Ω = 25Ω

Potential difference across 12 Ω resistor i.e. V = current × resistance = 0.24 × 12 = 2.88V
Reading of ammeter is 0.24 A and reading of voltmeter is 2.88 V.

In-text Questions (Page 216)

Question 1.
Judge the equivalent resistance when the following are connected in parallel:
(a) 1 Ω and 10⁶ Ω
(b) 1 Ω, 10³ Ω and 10⁶ Ω
Answer:
(a) The equivalent resistance of two resistances 1 Ω and 10⁶ Ω connected in parallel will be less than 1 Ω. This is because when a number of resistances are connected in parallel, then their equivalent resistance is less than the smallest individual resistance (which is 1 Ω in this case).
(b) The equivalent resistance of three resistances 1 Ω,10³ Ω and 10⁶ Ω connected in parallel will be less than 1 Ω.

Question 2.
An electric lamp of 100 Ω, a toaster of resistance 50 Ω, and a water filter of resistance 500 Ω are connected in parallel to a 220 V source. What is the resistance of an electric iron connected to the same source that takes as much current as all three appliances, and what is the current through it?
Answer:
The combined resistance R of three resistors (or electrical devices) R₁, R₂ and R₃, connected in parallel is given by the formula:
\(\frac{1}{R}=\frac{1}{R_{1}}+\frac{1}{R_{2}}+\frac{1}{R_{3}}\)
Here, Resistance of electric lamp, R₁ = 100 Ω
Resistance of toaster, R₂ = 50 Ω
and, Resistance of water filter, R₃ = 500 Ω
Putting these values of R₁, R₂ and R₃ in the above formula, we get:

Thus, the resistance of electric iron which takes the same current as drawn by all the three appliances will be 31.25 Ω.
Now, Potential difference, V = 220 V
Current, I = ? (To be calculated)
and, Resistance, R = 31.25 Ω (Calculated above)

Thus, the current passing through the electric iron is 7.04 amperes.

Question 3.
What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?
Answer:
The advantages of connecting electrical devices in parallel are the following:
(i) In parallel circuits, if one electrical appliance stops working due to some defect, even then all other appliances keep working normally. On the other hand, in a series circuit, if one electrical appliance stops working due to some defect, then all the other appliances also stop working (because the whole circuit is broken).

(ii) In parallel circuits, each electrical appliance has its own switch due to which it can be turned on or off independently, without affecting the other appliances. In a series circuit, all the electrical appliances have only one switch due to which they cannot be turned on or off independently.

(iii) In parallel circuits, each electrical appliance gets the same voltage as that of the battery due to which all the appliances work properly. In a series circuit, the appliances do not get the same voltage as that of the battery because the voltage is shared by all the appliances.

(iv) In the parallel connection of electrical appliances, the overall resistance of the circuit is reduced due to which the current from the battery is high and hence each electrical appliance can draw the required amount of current. In the series connection of electrical appliances, the overall resistance of the circuit cannot draw sufficient current for their proper working.

Question 4.
How can three resistors of resistances 2 Ω, 3 Ω, and 6 Ω be connected to give a total resistance of (a) 4 Ω, and (b) 1 Ω ?
(a) In order to obtain a total resistance 4 Ω from three resistors of 2 Ω, 3 Ω and 6 Ω:
(i) First connect the two resistors of 3 Ω and 6 Ω in parallel to get a total resistance of 2 Ω. This is because in parallel combination:

(ii) Then the parallel combination of 3 Ω and 6 Ω resistors (which is equivalent to 2 Ω resistance) is connected in series with the remaining 2 Ω resistor to get a total resistance of 4 Ω. This is because in series combination:
R = R₁ + R₂
R = 2 + 2
R = 4Ω
The arrangement of three resistors of 2 Ω, 3 Ω and 6 Ω which gives a total resistance of 4 Ω can now be represented as follows:

Thus, we can obtain a total resistance of 4 Ω by connecting a parallel combination of 3 Ω and 6 Ω resistors in series with 2 Ω resistor.

(b) In order to obtain a total resistance of 1 Ω from the three resistors of 2 Ω, 3 Ω and 6 Ω, all the three resistors should be connected in parallel. This is because in parallel combination:

Question 5.
What is (a) the highest, and (b) the lowest, total resistance that can be secured by the combination of four coils of resistance 4 Ω, 8 Ω,12 Ω and 24 Ω ?
Answer:
(a) The highest resistance can be secured (or obtained) by connecting all the four coils in series. In this case:
R = R₁ + R₂ + R₃ + R₄
R = 4 + 8 + 12 + 24
R = 48 Ω
Thus, the highest resistance which can be secured is 48 ohms.

(b) The lowest resistance can be secured by connecting all the four coils in parallel. In this case:

Thus, the lowest resistance which can be secured is 2 ohms.

In-text Questions (Page 218)

Question 1.
Why does the cord of an electric heater not glow while the heating element does?
Answer:
The heating element of an electric heater is made of an alloy (such as nichrome) which has high resistance whereas the cord is made of copper metal which has very, very low resistance. The heating element glows because it becomes red-hot due to the large amount of heat produced on passing current (because of its high resistance). On the other hand, the connecting cord of the electric heater made of copper does not glow because negligible heat is produced in it by passing the same current (due to its extremely low resistance).

Question 2.
Compute the heat generated while transferring 96000 coulomb of charge in one hour through a potential difference of 50 V.
Answer:
First of all we will calculate the current (I) by using the given values of charge (Q) and time (t). We know that:
Current, I = \(\frac{\mathrm{Q}}{t}=\frac{9600 \mathrm{C}}{1 \mathrm{~h}}=\frac{96000 \mathrm{C}}{60 \times 60 \mathrm{~s}}\)
or, I = 26.67 A …………(1)
We will now calculate the resistance using Ohm’s Law
Resistance, R = \(\frac{V}{I}=\frac{50 \mathrm{~V}}{26.67 \mathrm{~A}}\)
or R = 1.87 Ω …….(2)
and, Time, t = 1h = 60 × 60s = 3600 s ……(3)
Heat generated, H = I² × R × t = (26.67)² × 1.87 × 3600 J = 4788397 J = 4.79 × 10⁶ J or 4.8 × 10⁶ J
Thus, the heat generated is 4.8 × 10⁶ joules.

Question 3.
An electric iron of resistance 20 Ω takes a current of 5 A. Calculate the heat developed in 30 s.
Answer:
Here, Current, I = 5 A
Resistance, R = 20 Ω
and, Time, t = 30 s
Now, Heat produced, H = I² × R × t ⇒ H = (5)² × 20 × 30
H = 25 × 20 × 30 ⇒ H = 15000 J
Thus, the heat developed is 15000 joules.

In-text Questions (Page 220)

Question 1.
What determines the rate at which energy is delivered by a current?
Answer:
Electric power of the appliance.

Question 2.
An electric motor takes 5 A from a 220 V line. Determine the power of the motor and the energy consumed in 2 h.
Answer:
Here, Voltage, V = 220 V and, Current, I = 5 A
Now, Power, P = V × I
So, P = 220 × 5 W
∴ P = 1100 W
Thus, the power of the motor is 1100 watts.
Now, Power, P = 1100 W (Calculated above)
Time, t = 2h = 2 × 60 × 60 s = 7200 s
So, Energy, E = P × t
E = 1100 × 7200 J
E = 7.92 × 10⁶ J
Thus, the energy consumed is 7.92 × 10⁶ joules.

Bihar Board Class 10 Science Chapter 12 Electricity Textbook Questions and Answers

Question 1.
A piece of wire of resistance R is cut into five equal parts. These parts are then connected in parallel. If the equivalent resistance of this combination is R’, then the ratio R/R’ is:
(a) 1/25
(b) 1/5
(c) 5
(d) 25
Answer:
After cutting the wire, resistance of each part = \(\frac{\mathrm{R}}{5}\)
Equivalent resistance when these parts connected in parallel.

Question 2.
Which of the following terms does not represent electrical power in a circuit?
(a) I²R
(b) IR²
(c) VI
(d) V²/R
Answer:
Electric power
P = VI = (IR) I = I²R = \(\left(\frac{\mathrm{V}^{2}}{\mathrm{R}^{2}}\right) \mathrm{R}=\frac{\mathrm{V}^{2}}{\mathrm{R}}\)
So, IR² does not represent electric power in circuit.

Question 3.
An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be
(a) 100 W
(b) 75 W
(c) 50 W
(d) 25 W
Answer:

Here, operating voltage = 110 V
P = \(\frac{(110)^{2}}{484}\) = 25 W
(d) is correct answer.

Question 4.
Two conducting wires of the same material and of equal lengths and equal diameters are first connected in series and then parallel in a circuit across the same potential difference. The ratio of heat produced in series and parallel combinations would be
(a) 1: 2
(b) 2 : 1
(c) 1 : 4
(d) 4 : 1
Answer:
Since both wires are made up of same material and all other parameters are identical,
so, resistance of both the wires is same. Let it be R. When connected in series, their equivalent resistance is given by
R_eq = R₁ + R₂ = R + R = 2R
When connected in parallel, their equivalent resistance is given by

(c) is the correct answer.

Question 5.
How is a voltmeter connected in the circuit to measure the potential difference between two points?
Answer:
A voltmeter is always connected in parallel in the circuit across the points between which the potential difference is to be determined.

Question 6.
A copper wire has diameter 0.5 mm and resistivity of 1.6 × 10^-8 Ω m. What will be the length of this wire to make its resistance 10 Ω? How much does the resistance change if the diameter is doubled?
Answer:
Given, diameter of wire, D = 0.5 mm = 0.5 × 10^-3 m
Resistivity of copper, ρ = 1.6 × 10^-8 Ω m
Resistance = 10 Ω


As R ∝ \(\frac{1}{r^{2}} \propto \frac{1}{D^{2}}\), when D doubled, resistance becomes \(\frac {1}{4}\) times.

Question 7.
The values of current I flowing in a given resistor for the corresponding values of potential difference V across the resistor are given below:

Plot a graph between V and I and calculate the resistance of that resistor.
Answer:

Taking two points A and B
A(0.5 A, 1.6 V) and B (1.0 A, 3.4 V)
Slope = \(\frac{\Delta \mathrm{V}}{\Delta \mathrm{I}}\)
Here, ΔV = 1.8 V, ΔI = 0.5 A
R = \(\frac{\Delta \mathrm{V}}{\Delta \mathrm{I}}=\frac{1.8 \mathrm{~V}}{0.5 \mathrm{~A}}\) = 3.6 Ω

Question 8.
When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor.
Answer:
Here V = 12 V, I = 2.5 mA = 2.5 × 10^-3 A
Resistance = \(\frac{V}{I}=\frac{12 V}{2.5 \times 10^{-3} \mathrm{~A}}\) = 4800 Ω = 4.8 kΩ

Question 9.
A battery of 9 V is connected in series with resistors of 0.2 Ω, 0.3 Ω, 0.4 Ω, 0.5 Ω and 12 Ω, respectively. How much current would flow through the 12 Ω resistor?
Answer:
Equivalent resistance = 0.2 Ω + 0.3 Ω + 0.4 Ω + 0.5 Ω + 12 Ω
= 13.4 Ω
Current through circuit, I = \(\frac{\mathrm{V}}{\mathrm{R}_{e q}}=\frac{9 \mathrm{~V}}{13.4 \Omega}\) = 0.67 A
In series, the current flowing through all resistor is same. Thus, current flowing through 12 Ω resistor = 0.67 A.

Question 10.
How many 176 Ω resistors (in parallel) are required to carry 5 A on a 220 V line?
Answer:
Given, I = 5 A, V = 220 V
Resistance of the circuit, R = \(\frac{\mathrm{V}}{\mathrm{I}}=\frac{220 \mathrm{~V}}{5 \mathrm{~A}}\) = 44 Ω
Resistance of each resistor, r = 176 Ω
In case of parallel combination of identical resistors

Number of resistors required = 4

Question 11.
Show how you would connect three resistors, each of resistance 6 Ω, so that the combination has a resistance of (i) 9 Ω (ii) 4 Ω.
Answer:
1. For getting equivalent resistance R_eq = 9Ω two resistors will be connected in parallel and the third resistors will be connected in series with this parallel combination.

2. For getting equivalent resistance R_eq = 4 Ω two resistors should be connected in series. The combination of which will lead to equivalent of 12 Ω afterwards connecting this 12 Ω resistor with 6 Ω resistor in parallel, the overall equivalent resistance will be 4 Ω.

Question 12.
Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W. How many lamps can be connected in parallel with each other across the two wires of 220 V line if the maximum allowable current is 5 A?
Answer:

Question 13.
A hot plate of an electric oven connected to a 220 V line has two resistance coils A and B, each of 24 Ω resistance, which may be used separately, in series, or in parallel. What are the currents in the three cases?
Ans. Given, potential difference = 220 V
Resistance of each coil R_A = R_B = 24 Ω
(i) When each coil A or B is connected separately, current through each coil i.e.,

(ii) When coil A and B connected in parallel equivalent resistance in the circuit

(iii) When coil A and B are connected in series equivalent resistance

Question 14.
Compare the power used in the 2 Ω resistor in each of the following circuits: (i) a 6 V battery in series with 1 Ω and 2 Ω resistors, and (ii) a 4 V battery in parallel with 12 Ω and 2 Ω resistors.
Answer:

In a parallel circuit, potential (V) across each resistor is the same and is equal to the potential applied across the circuit.
Power dissipation through 2 Ω resistor

Question 15.
Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V?
Answer:

Question 16.
Which uses more energy, a 250 W TV set in 1 hour, or a 1200 W toaster in 10 minutes?
Answer:
Energy used by 250 W TV set in 1 hour = (250 W) (1 h) = 250 Wh
Energy consumed by 1200 W toaster in 10 min = \(\left(\frac{1}{6} h\right)\) = 1200 W × \(\frac {1}{6}\) h = 200 Wh
Energy consumed by 1200 W toaster in 10 minutes is less than energy consumed by 250 W TV set in 1 hour.
Hence energy consumed by the TV set is more.

Question 17.
An electric heater of resistance 8 Ω draws 15 A from the service mains for 2 hours. Calculate the rate at which heat is developed in the heater.
Answer:
Given, I = 15A, R = 8Ω, t = 2h
Rate at which heat is developed i.e., electric power
P = I²R = (15)² × 8 = 1800 W = 1800 J/S.

Question 18.
Explain the following:
(а) Why is the tungsten used almost exclusively for filament of electric lamps?
(b) Why are the conductors of electric heating devices, such as bread-toasters and electric irons, made of an alloy rather than a pure metal?
(c) Why is the series arrangement not used for domestic circuits?
(d) How does the resistance of a wire vary with its area of cross-section?
(e) Why are copper and aluminium wires usually employed for electricity transmission?
Answer:
(a) Tungsten has high melting point (3380°C). It does not melt and becomes very hot emitting light.
(b) The resistivity of an alloy is generally higher than that of pure metals and alloys do not oxidise readily at high temperatures.
(c) In series arrangement, if any one of the appliances fails or is switched off, all the other appliances stop working.
(d) Resistance of a wire is inversely proportional to its area of cross-sectional area (A)
R ∝ \(\frac{1}{\mathrm{~A}}\)
(e) Copper and aluminium posses low resistivity and hence low energy losses.

Bihar Board Class 10 Science Chapter 12 Electricity Textbook Activities

Activity 12.1 (NCERT Textbook Page 203-204)

Discussion and Conclusion:
The graph of V and I is a straight line passing through origin and slope of graph is equal to resistance

Activity 12.2 (NCERT Textbook Page 205)

Discussion and Conclusion:
The readings of ammeter are different for different components. This is due to the reason that resistances of all the components are different.

Activity 12.3 (NCERT Textbook Page 206)

Discussion and Conclusion:

• When the length of a wire is doubled, the resistance of the wire becomes twice as R ∝ l and current becomes half as I = \(\frac{\mathrm{V}}{\mathrm{R}}\)
• When the wire is replaced by a thicker nichrome wire, the resistance of wire decreases as R ∝ \(\frac{1}{\mathrm{~A}}\) and current increases as I = \(\frac{\mathrm{V}}{\mathrm{R}}\)
• When the nichrome wire is replaced by a copper wire of same length and cross-section, current decreases as resistivity of nichrome is greater as R ∝ p.
• Resistance of a wire depends on the resistivity of the material, length of wire and area of cross-section. R = ρ\(\frac{l}{\mathrm{~A}}\)

Activity 12.4 (NCERT Textbook Page 210)

Discussion and Conclusion:

• Here total resistance, R = 1Ω + 2Ω + 3Ω = 6Ω, Reading of ammeter is found to be around 6V/6Ω = 1A.
• When the position of the ammeter is changed, the reading remains the same.

Activity 12.5 (NCERT Textbook Page 211)

Discussion and Conclusion:

• Potential difference across the series combination is equal to potential difference across the two terminals of the battery.
• Relation between potential drop across battery and resistors V = V₁ + V₂ + V₃.

Activity 12.6 (NCERT Textbook Page 213-214)

Discussion and Conclusion:

• Potential difference across each resistor is same.
• Net current is equal to the sum of current through each resistor.

Bihar Board Class 10 Science Solutions Chapter 16 Management of Natural Resources

Bihar Board Class 10 Science Chapter 16 Management of Natural Resources InText Questions and Answers

In-text Questions (Page 269)

Question 1.
What changes can you make in your habits to become more environment friendly?
Answer:
The changes to become more environment friendly are:

• Reduce the use of fossil fuels.
• Repairing the water taps if leakage is seen.
• Planting trees.
• No use of plastic bags.
• Reuse the empty bottles of pickles and jams.
• Recycle the recyclable materials for use.

Question 2.
What would be the advantages of exploiting resources with short-term aims?
Answer:
Advantages for exploiting resources for short-term aims are:

• Increase profits without any accountability.
• Fulfil the needs of the present generation.

Question 3.
How would these advantages differ from the advantages of using a long-term perspective in managing our resources?
Answer:
A long-term perspective would be more advantageous as it will ensure the fulfilment of needs of the present generation and conserve the resources for the benefit of the future generations too.

This approach will also be helpful in avoiding overexploitation of resources for short term gains.

Question 4.
Why do you think there should be equitable distribution of resources? What forces would be working against an equitable distribution of our resources?
Answer:
Equitable distribution of resources is necessary so that benefits are also enjoyed by the poor people instead of being in hands of the rich and powerful people.

The social structure, the monetary gap and the social status work against equitable distribution of resources between the poor and the rich and powerful people.

In-text Questions (Page 273)

Question 1.
Why should we conserve forest and wildlife?
Answer:

• To preserve the biodiversity as its loss disturbs the ecological stability.
• Forest trees prevent floods and soil erosion.
• Various benefits like fuelwood, fruits, medicines, etc. are obtained by people from forests.

Question 2.
Suggest some approaches towards the conservation of forests.
Answer:

• Felling of trees indiscriminately should be banned.
• Creating awareness among people for forest conservation.
• Involving local people in forest conservation as was done in Arabari forests of West Bengal.
• Banning hunting of wild animals to protect wildlife.
• Encouraging planting more trees.

In-text Questions (Page 276)

Question 1.
Find out about the traditional systems of water harvesting/management in your region.
Answer:
The traditional systems of water harvesting are ponds, tanks, lakes and other water reservoirs which were called differently based on the regions. Example: Kulhs in Himachal Pradesh, Khadins, tanks and Nadis in Rajasthan, Kattas in Karnataka, etc. Baoli were used in Delhi region to store water in olden days.

Question 2.
Compare the above system with the probable systems in hilly/mountainous areas or plains or plateau regions.
Answer:
In hilly areas like Himachal Pradesh, the local system of canal irrigation called kulhs were developed in which water flowing in the streams was diverted to man-made channels. These channels took water to different villages down the hillside.

In level terrains like plains or plateau, crescent shaped earthen embankments or straight concrete and rubble ‘check dams’ are built to store running water.

Question 3.
Find out the source of water in your region/locality. Is water from this source available to all people living in that area?
Answer:
Water drawn from the rivers or tubewells is supplied by government through pipes to the homes of people in our locality. Only the areas approved by the local municipal bodies get the supply of water in this way.

Bihar Board Class 10 Science Chapter 16 Management of Natural Resources Textbook Questions and Answers

Question 1.
What changes would you suggest in your home in order to be environment-friendly?
Answer:
The following of 3 R’s is necessary to be environment-friendly in home, which are:
Reduce: Use less and not to waste any resource. For example, Water and electricity.
Recycle: Segregate the waste that can be recycled and make required things by using them. For example, Paper and plastic bottles.
Reuse: Use the things again and again. For example, Bottles of jams and pickles, plastic carry bags.

Question 2.
Can you suggest some changes in your school which would make it environment friendly?
Answer:

• Switch off the lights and fans when not necessary.
• Plant trees in the school campus.
• Recycle waste paper.
• Segregate wastes into biodegradable and non-biodegradable and put them in separate dustbins.

Question 3.
We saw in this chapter that there are four main stakeholders when it comes to forests and wildlife. Which among these should have the authority to decide the management of forest produce? Why do you think so?
Answer:
The stakeholders in the conservation of forests are:

• Local People: Those who are dependent on forests for their survival.
• Forest Department: Government who owns the land and controls resources
• Industrialists: Those who use various forests
• Wildlife enthusiasts: Those who want to conserve nature.

I am of the opinion that the local people should have the authority to decide the management of forest produce as they never overexploit the forest resources. They utilise them as per their needs and try to replenish them too. Their efforts can help in fulfilling and balancing the needs of the other three stakeholders in the conservation of forests.

Question 4.
How can you as an individual contribute or make a difference to the management of
(a) forests and wildlife, (b) water resources and (c) coal and petroleum?
Answer:
As an individual we can contribute or make a difference to the management of
(a) Forests and wildlife: By creating awareness among people for their conservation and planting more and more trees.
(b) Water resources: By turning off tap when not in use, repair leaking taps, use treated water for washing cars.
(c) Coal and petroleum: By using renewable sources of energy like solar energy, switching over to cleaner fuels like CNG, using solar heaters, using LED lights, less use of private vehicles.

Question 5.
What can you as an individual do to reduce your consumption of the various natural resources?
Answer:
As an individual we can reduce our consumption of the various natural resources by

• Taking a bus, public transport or walking/cycling instead of a private vehicle.
• Using LED bulbs in homes instead of normal bulbs.
• Taking the stairs instead of lift.
• Wearing an extra sweater on cold days instead of burning fossil fuels for warmth.

Question 6.
List five things you have done over the last one week to
(a) Conserve our natural resources.
(b) Increase the pressure on our natural resources.
Answer:
(a) Five things done to conserve our natural resources are:

• Switched off fans when not in use.
• Changed the lights in home to LED bulbs.
• Used public transport.
• Recycled waste paper.
• Reused the empty jam bottles to store kitchen grocery.

(b) Five things done to increase pressure on our natural resources are:

• Kept the lights switched on unnecessarily.
• Washed the car with water fit for drinking.
• Used car to travel even for short distances.
• Burnt paper wastes.
• Threw away old envelopes which could have been recycled.

Question 7.
On the basis of the issues raised in this chapter, what changes would you incorporate in your life-style in a move towards a sustainable use of our resources?
Answer:
The changes which I would incorporate in my life-style to move towards a sustainable use of our resources will be:

• Conserve water and electricity.
• Recycle the waste paper, plastic polybags, etc.
• Do water harvesting to recharge ground water level.
• Minimise use of fossil fuels and switch over to solar energy.
• Use public transport for travel instead of private vehicle.

Bihar Board Class 10 Science Chapter 16 Management of Natural Resources Textbook Activities

Activity 16.1 (Textbook page 266)

Euro norms refer to the permissible emission levels from both petrol and diesel vehicles, which have been implemented in Europe. However in India, the government has adopted the Euro norms for available fuel quality and the method of testing. Euro norms have been given a name of Bharat-I, Bharat-IV, etc. Refer-https://en.wikipedia.org/wiki/European_emission_standards https://en.wikipedia.org/wiki/Carbon_credit

The ways in which you can reduce the carbon emission levels are:
(i) Use public transport (ii) Conserve energy (iii) Manage resources in a better way (iv) Conservation of nature and natural resources (v) Creating awareness among people regarding need of conservation (vi) Plant more trees (vii) Reduce the carbon emissions from industries (viii) Strictly adhere to the pollution under control norms (ix) Use devices in industries to reduce carbon emissions (x) Proper planning and switching over to sources that emit less carbon

Activity 16.2 (Textbook page 266)

Refer-http://www.findouter.com/Asia/India/Science and Social Science/Environment/Environmental Organisations

We can contribute towards the same cause by actively participating in the activities of such organisations and creating awareness among the people of our locality and society.

Activity 16.3 (Textbook page 268)

Yes, the pollution levels of water can be indicated by the levels of pH of the water body. However, certain other variables like the Coliform count, Total Dissolved Solids and Conductivity of Suspended sediment etc. can supplement the data regarding the levels of pollution of the water.

Activity 16.4 (Textbook page 268)

The changes one would observe are that

• Forests cleared to use the land for agricultural fields.
• New houses have been constructed in place of mud huts.
• The non-metalled roads have replaced the metalled roads.

The destruction of forests to make agricultural fields should be minimised.

Activity 16.5 (Textbook page 270)

The forest produce which we use are- resins, gums, timber or wood, fruits, medicines, etc.
The persons living near a forest would use:

• timber-wood
• fruits
• spices
• wood to make paper
• tendu leaves for making bidis
• products of plantation of one species of plants
• resins and gums

The persons living in forest would use them for:

• fire-wood to be used as fuel
• fruits
• collection of honey
• fodder for cattle
• making implements for agriculture and construction
• medicines
• material for thatch roof of their huts

Activity 16.6 (Textbook page 271)

• Tendu leaves are used for making bidis
• Wood obtained from trees used in paper industry, furniture industry; wood from Salix species for making cricket bats etc.

No, these industries are not sustainable in the long run as they are being overexploited for human needs. So, we need to control our consumption of the products obtained from such trees.

Activity 16.7 (Textbook page 273)

(a) A lot of trees and vegetation is needed to be cut down for building rest houses for tourists in national parks. This is not good for the ecological balance of the area. Making such rest houses in National parks increases the levels of air pollution, noise pollution, etc. and the uncontrolled littering in such areas is a common sight these days which is very detrimental for the animals living in the area.

(b) Grazing animals in the national parks if carried out in an uncontrolled manner can lead to soil erosion as the grasses which bind the soil particles will not be there and so soil would be easily washed away during rains. The water holding capacity and ability to sustain the growth of larger trees will also be affected in absence of grass cover. Even the animals residing in the forest would be deprived of their food if large scale overgrazing is carried out.

(c) Tourists throwing plastic bottles/covers and other litter in national parks plays a havoc on the nature as these substances are non-biodegradable and they take several years to get completely degraded. The toxins which are released during their degradation further pollute the soil of the national parks. Plastics can choke the alimentary canals of the animals swallowing them and lead to their death. These substances also give an unpleasant look to the area due to their littering here and there.

Activity 16.8 (Textbook page 273)

The use of water resources merely for entertainment of few people when a large chunk of people from villages are suffering from chronic water shortage is very pathetic and shameful. Such a misuse of water should be stopped and the water should be diverted to the village for the use by the people during shortage of water. We need to manage our resources in a way that the distribution is equitable and useful to a large section of the society rather than catering to the needs of a few people. A big solution can be provided to the chronic water shortages in the village if rainwater is properly channelized, wastage of water is reduced, people are sensitised towards the need for conservation of water and the water resources should be managed in the most efficient way to fulfil the goals of sustainable development.

Activity 16.9 (Textbook page 273)

The maximum rainfall is received in the North east part of India and the western coastal regions of India. Mawsynram is the place where highest rainfall has been recorded till date. The area with least amount of rainfall are the Northwestern parts of India which include the states like Rajasthan, Haryana, parts of Gujarat and Punjab, so problems of water scarcity is more prevalent in these regions. The map showing the rainfall patterns in India is shown below:

Activity 16.10 (Textbook page 277)

The consumption of coal and petroleum can be reduced in the following ways:

• More use of public transport than personal vehicles.
• Conserving electricity by switching off fans and lights, when not in use.
• Use of solar cookers for cooking food in the areas which get good amount of sunlight.
• Use alternative sources of energy like the solar energy, wind energy etc.
• Use of biogas to generate electricity and to use as domestic fuel.
• The energy efficient devices like LED’s, higher Bureau of energy efficiency rating products etc.
• Save fuel by using bicycles or walking for covering short distances.
• An extra sweater can be worn in winters to save fuel/electricity used in a heating device.
• Less use of lavish lightning and decorations in weddings and public functions.
• Keeping the engines of vehicles well tuned and serviced to save fuel.

Activity 16.11 (Textbook page 278)

Euro norms refer to the permissible emission levels from both petrol and diesel vehicles, which have been implemented in Europe (EU-European Union). The Euro norms require manufacturers to reduce the existing polluting Emission Levels from the exhausts in a more efficient manner by making certain technical changes in the engines of the vehicles. The Euro-I norms was implemented from the year 1992-93. Euro-1 norms in India are known as India 2000 since it was implemented from 1/4/2000 in India. The changes required to be made by manufacturers for a euro I compliant car focussed primarily on: (a) catalyser capacity increase (b) tri-metal coating in the catalyser (c) exhaust gas recirculation (d) carburettor retuning (e) secondary air intake. The Euro-I and Euro-II norms are given in the table below:

Bihar Board Class 10 Science Solutions

Bihar Board Class 10 Science Solutions Chapter 15 Our Environment

Bihar Board Class 10 Science Chapter 15 Our Environment InText Questions and Answers

In-text Questions (Page 257)

Question 1.
Why are some substances biodegradable and some non-biodegradable?
Answer:
The bacterial and fungal enzymes degrade the complex organic compounds present in the dead remains of plants and animals into simpler substances, so such wastes are called biodegradable. However, some wastes like glass, plastics, etc. cannot be degraded by these enzymes due to which they are persistent in the environment for many years. These are called non-biodegradable substances.

Question 2.
Give any two ways in which biodegradable substances would affect the environment.
Answer:
The biodegradable wastes can affect the environment as:

• Their huge heaps act as breeding grounds for flies and mosquitoes which lead to spread of diseases like typhoid, tuberculosis, cholera, etc.
• During decomposition of these biodegradable wastes, foul smell is produced which makes people feel uncomfortable.

Question 3.
Give any two ways in which non-biodegradable substances would affect the environment.
Answer:
The non-biodegradable substances would affect the environment as:

• Some of the harmful pesticides and chemicals lead to loss of soil fertility and creates imbalance in the food chains.
• Their increased volumes in the garbage dumps due to non-decomposition create problems for many animals. For example, plastics eaten by cows can choke them to death.

In-text Questions (Page 261)

Question 1.
What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
Answer:
Each step or level in the food chain where transfer of energy takes place is called a trophic level. Example: Grass → Insect → Frog → Snake
First Trophic Level : Grass is Producer;
Second Trophic Level : Insect is Primary consumer;
Third Trophic Level : Frog is Secondary consumer;
Fourth Trophic Level : Snake is Tertiary consumer

Question 2.
What is the role of decomposers in the ecosystem?
Answer:
The complex organic substances present in the dead remains of plants and animals are broken down and converted into simpler inorganic substances by the decomposers. Thus they help in recycling of nutrients and cleansing the environment.

In-text Questions (Page 264)

Question 1.
What is ozone and how does it affect any ecosystem?
Answer:
Ozone (O₃) is a molecule formed by three atoms of oxygen. The ozone present in the lower parts of the atmosphere is a deadly poison and harmful to organisms. But, the ozone present in the higher levels of the atmosphere is good ozone as it shields the organisms against the harmful ultraviolet rays of the Sun (that cause skin cancer) by absorbing them. It is formed by the action of ultraviolet radiation on oxygen molecule to convert it into free oxygen atom. These free oxygen atoms combine with molecular oxygen to form ozone.
\(\mathrm{O}_{2} \stackrel{\mathrm{UV}}{\longrightarrow} \mathrm{O}+\mathrm{O}\)
\(\mathrm{O}+\mathrm{O}_{2} \longrightarrow \underset{(\mathrm{Ozone})}{\mathrm{O}_{3}}\)

Question 2.
How can you help in reducing the problem of waste disposal? Give any two methods.
Answer:
A collective effort by all the people can be very instrumental in reducing the problem of waste disposal. This can be done by:

• Recycling and reusing the wastes before disposing them off completely in the garbage bins.
• Segregate the various wastes as bio-degradable, non-biodegradable and hazardous wastes by using separate bins for each kind of waste.

Bihar Board Class 10 Science Chapter 15 Our Environment Textbook Questions and Answers

Question 1.
Which of the following groups contain only biodegradable items?
(a) Grass, flowers and leather
(b) Grass, wood and plastic
(c) Fruit-peels, cake and lime-juice
(d) Cake, wood and grass
Answer:
(a) Grass, flowers and leather

Question 2.
Which of the following constitute a food-chain?
(a) Grass, wheat and mango
(b) Grass, goat and human
(c) Goat, cow and elephant
(d) Grass, fish and goat
Answer:
(b) Grass, goat and human

Question 3.
Which of the following are environment-friendly practices?
(a) Carrying cloth-bags to put purchases in while shopping
(b) Switching off unnecessary lights and fans
(c) Walking to school instead of getting your mother to drop you on her scooter
(d) All of the above
Answer:
(d) All of the above

Question 4.
What will happen if we kill all the organisms in one trophic level?
Answer:
If we kill all the organisms in one trophic level, then it will cause imbalance in the ecosystem as transfer of food energy to the next level will stop. An overpopulation of the organisms in the previous trophic level will also take place. This will disturb the ecological balance.

Question 5.
Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem?
Answer:
The impact of removing all the organisms in a trophic level will be same as the impact for different trophic levels because it would lead to

• Starvation and death of organisms in the next trophic level as energy transfer to the next level would stop. For example, if all producers are killed, herbivores will be affected as no food will be available for them.
• Overpopulation in the previous level as no organism will be available in the next trophic level to feed on them.

Since all the organisms are interdependent on each other in an ecosystem, it will result in an imbalance in the ecosystem if organisms of any trophic level are removed.

Question 6.
What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Answer:
The harmful chemicals like pesticides are neither metabolised nor excreted by the organisms. They get accumulated in the body of the organisms due to which their concentration goes on increasing in the successive trophic levels. This phenomenon is called biological magnification.

The level of this magnification goes on increasing as we move up the trophic levels. So, the concentration of these chemicals is highest in the human beings as they occupy the topmost trophic level.

Question 7.
What are the problems caused by the non-biodegradable wastes that we generate?
Answer:
The following problems are caused by the non-biodegradable wastes:

• They are not decomposed and get accumulated in the environment. They contaminate the soil and water resources.
• Their increased volumes in the garbage dumps due to non-decomposition create problems for many animals. Plastics eaten by cows or other stray animals can choke them to death.
• Their accumulation makes the land unfit for other purposes, makes it infertile.
• The rag pickers are exposed to harmful chemicals and toxins present in these kinds of wastes.
• They enter the food chain and become harmful to human beings and other animals.

Question 8.
If all the waste we generate is biodegradable, will this have no impact on the environment?
Answer:
Even the biodegradable wastes have an impact on the environment in the following ways:

• A foul smell is released during their decomposition. Also, some harmful gases are released which cause air pollution.
• The heaps of such biodegradable wastes act as a breeding ground for disease causing organisms like flies and mosquitoes.

Question 9.
Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Answer:
Ozone present in stratosphere acts as a shield which absorbs the harmful ultraviolet rays of the Sun. Damage to the ozone or its depletion will lead to non absorption of UV rays which cause skin cancer, ageing, cataract, etc. Damage to ozone is most prominent in Antarctica region where it’s visible as a ozone hole.

Steps to limit ozone damage:

• The use of substances called CFCs (Chlorofluorocarbons) as refrigerants and in fire extinguishers should be reduced and these should be replaced by environment friendly substances.
• UNEP (United Nations Environment Programme) has forged an agreement to freeze CFCs production at 1986 levels by all countries.

Bihar Board Class 10 Science Chapter 15 Our Environment Textbook Activities

Activity 15.1 (Textbook page 256)

The materials like metallic containers, plastic bottles, bubble packs, broken footwear, etc. remain unchanged for longer periods of time. The materials which change their form and structure overtime are the empty cartons, kitchen wastes, torn clothes etc.

The fastest change is seen in spoilt food, vegetable peels, used tea leaves.

Activity 15.2 (Textbook page 257)

The non-biodegradable substances last from a few years to several million years. Biodegradable plastics are plastics that can be decomposed by the action of living organisms like bacteria. Under proper conditions, some biodegradable plastics can degrade to the point where microorganisms can completely metabolise them. They do not harm the environment in the way the non-biodegradable plastics harm because they are decomposed at a faster rate by the microorganisms and once decomposed they are no more a problem.

Activity 15.3 (Textbook page 258)

An aquarium becomes a self sustaining system once the above essential materials are provided in it. The water, oxygen and food are the resources which help in the life processes of organisms present in the aquarium. The aerator keeps providing fresh supply of oxygen in it. The biotic and the abiotic components interact among themselves to sustain the artificial ecosystem. We cannot leave the aquarium as such for a longer time as the growth of microorganisms like bacteria and fungi occurs which need to be removed in order to avoid infection of the fishes. Lakes and ponds are large ecosystems which do not need to be cleaned so frequently. But sometimes they need to be cleaned in order to avoid siltation or excessive growth of aquatic plants. Example is the recent cleaning of the Pushkar lake in Ajmer.

Activity 15.4 (Textbook page 259)

Yes, we have to take care not to put an aquatic animal which would eat others. Otherwise the ecosystem will not remain self-sustaining and can lead to imbalances in the processes and the whole ecosystem (aquarium).

The food chain present in the ecosystem would also consist of primary producers, primary consumers, secondary consumers, etc. Primary producers will be the phytoplanktons and the algae. Primary consumers will be zooplanktons. Secondary consumers will be small fishes followed by the larger fishes as the tertiary consumers. These groups are dependent on each other as the energy produced by the organisms at one level gets transferred from the lower level to the higher level. The aquatic organisms in the chain would be will be:
Phytoplanktons (producers) → zooplanktons (primary consumers) → small fishes (secondary consumers) → large fishes(tertiary consumers)

The producers can be considered of primary importance in an ecosystem. But, an aquarium being an artificial ecosystem, the role of human being is more in maintaining the supply of nutrients, aeration, energy, etc. to keep the ecosystem self sustaining type.

Activity 15.5 (Textbook page 261)

There is a big debate going on regarding the use of chemical pesticides as most of them like DDT once taken in by animals through the food products they consume, can neither be excreted nor metabolised. It starts accumulating in the body of the organism and as we go higher up the food chain, the concentration of harmful toxicant reaches higher levels. This phenomenon is called as biological magnification which is harmful for the health of human beings and other organisms too. Source of pesticides in the food items are the pesticides sprayed on plants or crops by humans to increase their levels of agricultural production. Yes, pesticides can enter our body from this source through other food products too as the various organisms are dependent upon each other for their survival.

The methods which can be applied are

• use of bio-control agents to protect loss of crop
• development and use pest resistant crops
• practice of organic farming

Activity 15.6 (Textbook page 262)

The chemical which has been highly detrimental to the ozone layer is the use of chlorofluorocarbons in the refrigerator, deo-sprays, etc. The harmful effect of these chemical was highlighted in 1985 when the ozone hole was detected in Antarctica. The various countries of the world met and signed the Montreal protocol in 1987 which laid down the roadmap to control the emission of ozone depleting substances.

Activity 15.7 (Textbook page 262)

The wastes generated in our homes are segregated in the various bins designated for keeping biodegradable, recyclable, non-biodegradable and hazardous wastes separately. The scavengers take away the wastes from the homes and dispose it off properly at the places meant for them so that they do not cause harm to other living organisms. The resident welfare association have designated scavengers who take the wastes away from the home. The recyclable materials are either recycled or sent to units which recycle the wastes for various other processes. The non-biodegradable and hazardous substances are disposed off by sending them to the landfill sites or by incineration.

Activity 15.8 (Textbook page 263)

Approximately 2-3 kg of waste is generated at home in a day. Approximately half of it is biodegradable. The waste generated per day in a classroom is approximately 1 kg. Almost all the waste generated in the classroom is biodegradable. The biodegradable waste can be put in compost pits and converted to compost or the recyclable ones can be recycled.

Activity 15.9 (Textbook page 263)

The sewage is treated in the sewage treatment plants. The plans are being made to ensure that no untreated sewage is discarded in the local water bodies. The local industries send their wastes to the sewage treatment plants where the harmful chemical and constituents are removed from it, before discharging it into the water bodies. Though some mechanisms are there to prevent soil and water from getting polluted by such wastes, other advanced systems are being implemented to control such pollution.

Activity 15.10 (Textbook page 263)

The electronic items thrown as e-wastes contain many harmful and hazardous substances like lead, cadmium, chromium, brominated flame retardants or polychlorinated biphenyls (PCBs).
Refer- http://ewasteguide.info/hazardous-substances
http://listverse.com/2013/01/27/10-ways-recycling-hurts-the-environment/http://www.livestrong.com article/181103-the-effect-of-recycling-plastic-water-bottles-on-the-environment/

Bihar Board Class 10 Science Solutions Chapter 14 Sources of Energy

Bihar Board Class 10 Science Chapter 14 Sources of Energy InText Questions and Answers

In-text Questions (Page 243)

Question 1.
What is a good source of energy?
Answer:
A good source of energy should have the following qualities:

• does a large amount of work per unit mass.
• cheap and easily available.
• easy to store and transport.
• safe to handle and use.
• does not cause environmental pollution.

Question 2.
What is a good fuel
Answer:
A good fuel should have the following qualities:

• high calorific value (give more heat per unit mass).
• bums without giving out any smoke or harmful gases.
• proper ignition temperature.
• cheap and easily available.
• convenient to store.
• bums smoothly.

Question 3.
If you could use any source of energy for heating your food, which one would you use and why?
Answer:
I will use LPG (Liquefied Petroleum Gas) for heating my food; because it is easily available in my kitchen, gives no smoke on burning and takes less time to do the job.

In-text Questions (Page 248)

Question 1.
What are the disadvantages of fossil fuels?
Answer:
Disadvantages of fossil fuels:

• They are non-renewable.
• They produce air pollutants on burning.

Question 2.
Why are we looking at alternate sources of energy?
Answer:
Because of growing population, the energy demand is rising. Fossil fuels are going to be exhausted in the near future and burning them is causing pollution. Hence, we need to find an alternate source of energy which is renewable and environment friendly.

Question 3.
How has the traditional use of wind and water energy been modified for our convenience?
Answer:
To use energy of flowing water, large dams are built to store huge amount of water at a height. The stored water is allowed to fall from a height which runs the turbine at the bottom of the dam to generate electricity. Similarly, the wind energy is used to generate electricity. For this purpose, the rotatory motion of windmill is used to turn the turbine of the electric generator.

In-text Questions (Page 253)

Question 1.
What kind of mirror; concave or convex or plain would be best suited for used in a solar cooker? Why?
Answer:
A solar cooker uses heat of the sunlight to cook food. A concave mirror is used in order to reflect and focus sunlight at a particular area. The mirror focuses all the incident sunlight at a point. The temperature at the point increases, thereby cooking and heating the food placed in that particular area.

Question 2.
What are the limitations of the energy that can be obtained from the oceans?
Answer:
Limitations of the energy obtained from the oceans are

• There are very few locations where dams can be built to utilise tidal energy.
• Cost of installation of power houses is extremely high and efficiency of plants is comparatively small.
• Power plants built in oceans or at sea-shores will need high continuous maintenance as chances of corrosion are extremely high.

Question 3.
What is geothermal energy?
Answer:
The energy which can be harnessed from the heat inside the earth is called geothermal energy.

Question 4.
What are the advantages of nuclear energy?
Answer:
Advantages of nuclear energy:

• A small amount of radioactive material can generate a huge amount of energy.
• It does not produce air pollution.
• A nuclear power plant is more efficient than other power plants.

In-text Questions (Page 253)

Question 1.
Can any source of energy be pollution free? Why or why not?
Answer:
No sources of energy can be pollution free. This is because operation of a device like in a solar cell and some other sources of energy may be pollution free but their installation may cause pollution.

Question 2.
Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?
Answer:
Hydrogen is a much cleaner energy source than CNG as it produces water vapour on burning. CNG (compressed natural gas) is derived from biomass and hence burning the CNG causes air pollution.

In-text Questions (Page 254)

Question 1.
Name two energy sources that you would consider to be renewable. Give reasons for your choices.
Answer:
Biomass and solar energy because these sources can be easily replenished.

Question 2.
Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choices.
Answer:
Coal and petroleum are two exhaustible sources of energy. These fuels were formed over millions of years ago and there are only limited reserves. If we continue to use them as at present rate, then these reserves will be exhausted very soon.

Bihar Board Class 10 Science Chapter 14 Sources of Energy Textbook Questions and Answers

Question 1.
A solar water heater cannot be used to get hot water on:
(а) sunny day
(b) a cloudy day
(c) hot day
(d) a windy day
Answer:
(b) a cloudy day

Question 2.
Which of the following is not an example of a biomass energy source?
(a) wood
(b) gobar-gas
(c) nuclear energy
(d) coal
Answer:
(c) nuclear energy

Question 3.
Most of the sources of energy we use represent stored solar energy. Which of the following is not ultimately derived from the Sun’s energy?
(a) geothermal energy
(b) wind energy
(c) nuclear energy
(d) biomass
Answer:
(c) nuclear energy

Question 4.
Compare and contrast fossil fuels and the sun as direct sources of energy.
Answer:
Fossil fuels:

1. The reserves of fossil fuels are limited i.e., exhaustible.
2. Burning of fossil fuels cause pollution.
3. Fossil fuels can provide energy at any required time.

Solar energy:

1. Solar energy is available in abundance i.e., inexhaustible.
2. Solar energy is pollution free.
3. Solar energy is available during daytime only and when there in no cloud.

Question 5.
Compare and contrast biomass and Hydroelectricity as direct sources of energy.
Answer:
Biomass:

1. The energy from biomass can be obtained by using a challah or a gobar gas plant.
2. Biomass is pollution free when only biogas is used.

Hydroelectricity:

1. Hydroelectricity requires construction of dam.
2. Hydroelectricity is totally pollution free.

Question 6.
What are the limitations of extracting energy from: (a) the wind (b) waves (c) tides?
Answer:
(a) Limitation of wind energy

• Wind speed is not uniform always.
• Big amount of investment is needed.
• Need a large area for plant installation.

(b) Limitation of wave energy

• Power output is variable in nature.
• Wave energy generation is expensive.

(c) Limitation of tidal energy

• Power output is variable.
• Power generation is intermittent.

Question 7.
On what basis would you classify energy sources as
(a) renewable and non-renewable?
(b) exhaustible and inexhaustible?
Are the options given in (a) and (b) the same?
Answer:
Yes, options are same.
Renewable and inexhaustible sources of energy are similar to each other while non-renewable and exhaustible sources are similar.

Renewable sources of energy are those which are inexhaustible i.e., which can be replaced as we use them and can be used to produce energy again and again, Examples: (a) solar energy (b) wind energy

Non-renewable sources of energy are those which are exhaustible and cannot be replaced once they have been used.

Question 8.
What are the qualities of an ideal source of energy?
Answer:
Qualities of an ideal source of energy:

• Has high calorific value
• Produces less smoke
• Produces less residue after burning
• Easy availability
• Inexpensive
• Easy to store and transport

Question 9.
What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?
Answer:
Advantages of solar cookers:

• Ecofriendly
• Renewable
• Used in rural areas
• Retains all the nutrients in food due to slow cooking

Disadvantages of solar cooker:

• Silicon cells are expensive.
• Solar radiations are not uniform over the earth’s surface.
• Cannot be used at night or on cloudy days.
• Cannot be used to make chapattis for frying as these require a temperature of 140°C or more. (Maximum temperature of 100°C only can be achieved in a solar cooker)

Question 10.
What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?
Answer:
Environmental consequences:

1. Air pollution is increasing due to burning of fossil fuels.
2. Construction of dam destroys large ecosystem.

Steps to reduce energy consumption:

1. Use energy efficient devices.
2. Extract maximum possible energy from fossil fuels.

Bihar Board Class 10 Science Chapter 14 Sources of Energy Textbook Activities

Activity 14.3 (Textbook Page 244-245)

Discussion and conclusion:
The tennis balls acts like a turbine and starts rotating. It transfer its rotational energy to the dynamo, which converts it rotational energy to electricity. The electric current from the dynamo passes through the bulb and lights it up.

Activity 14.5 (Textbook Page 249)

Discussion and conclusion:
The conical flask which is painted black is hotter than the one painted white. Black colour absorbs more heat.

Bihar Board Class 10 Science Solutions Chapter 13 Magnetic Effects of Electric Current

Bihar Board Class 10 Science Chapter 13 Magnetic Effects of Electric Current InText Questions and Answers

In-text Questions (Page 224)

Question 1.
Why does a compass needle get deflected when brought near a bar magnet?
Answer:
Magnetic compass needle and bar magnet both have magnetic field. When they are brought near each other, these magnetic fields interact with each other showing deflection in the needle.

In-text Questions (Page 228)

Question 1.
Draw magnetic field lines around a bar magnet.
Answer:

Question 2.
List the properties of magnetic lines of force.
Answer:
Properties of magnetic lines of force are listed below:

• Outside the magnet, the magnetic field lines are directed from N-pole of magnet towards S-pole. However, inside a magnet the field lines are directed from S-pole to N-pole. Thus magnetic field lines from a closed loop.
• The magnetic field line at any point, points in the direction of magnetic field at that point.
• The relative strength of magnetic fields is given by degree of closeness of the field lines. The magnetic field is strong in the region where the field lines are crowded.
• No two magnetic field lines can ever intersect with each other.

Question 3.
Why don’t two magnetic lines of force intersect each other?
Answer:
Magnetic field-lines do not cross each other. If they did, it would mean that at the point of intersection, the compass needle would point towards two directions, which is not possible.

In-text Questions (Page 229-230)

Question 1.
Consider a circular loop of wire lying in the plane of the table. Let the current pass through the loop clockwise. Apply the right-hand rule to find out the direction of the magnetic field inside and outside the loop.
Answer:
The magnetic field lines have been shown in figure given below. As per right-hand rule, we find that inside the loop, the magnetic field lines are directed perpendicular to the plane of paper in the inward direction. Outside the loop, magnetic field lines are directed out of the plane of paper.

Magnetic field lines of the field produced by a current carrying circular loop

Question 2.
The magnetic field in a given region is uniform. Draw a diagram to represent it.
Answer:
The uniform magnetic field is represented by parallel, equidistant lines of equal length as shown in figure.

Question 3.
Choose the correct option. The magnetic field inside a long straight solenoid-carrying current (a) is zero. (b) decreases as we move Uniform Magnetic Field Lines towards its end. (c) increases as we move towards its end. (d) is the same at all points.
Answer:
(d) is the same at all points.

In-text Questions (Page 231-232)

Question 1.
Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.) (a) Mass (6) Speed (c) Velocity (d) Momentum.
Answer:
(c) Velocity and (d) Momentum.

Question 2.
In Activity 13.7, how do we think the displacement of rod AB will be affected if (i) current in rod AB is increased; (ii) a stronger horse-shoe magnet is used; and (iii) length of the rod AB is increased?
Answer:
(i) If current in rod AB is increased, the displacement will also increase, (ii) If we use a stronger horse-shoe magnet then the displacement of rod AB will increase, (iii) If length of the rod is increased, force acting on it will increase and, hence, displacement of the rod will increase.

Question 3.
A positively-charged particle (alpha-particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is (a) towards south (b) towards east (c) downward (d) upward.
Answer:
(d) upward in accordance with Fleming’s left-hand rule, the direction of magnetic field is vertically upward.

In-text Questions (Page 233)

Question 1.
State Fleming’s left-hand rule.
Answer:
According to Fleming’s left-hand rule, stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular. If the first finger points in the direction of magnetic field and the second finger in the direction of current, then the thumb will point in the direction of motion or the force acting on the conductor.

Question 2.
What is the principle of an electric motor?
Answer:
The working principle of an electric motor is based on the magnetic effect of current. A current-carrying loop experiences a force and rotates when placed in a magnetic field. The direction of rotation of the loop is given by the Fleming’s left-hand rule.

Question 3.
What is the role of the split ring in an electric motor?
The split ring in the electric motor acts as a commutator. The commutator reverses the direction of current flowing through the coil after each half rotation of the coil. Due to this reversal of the current, the coil continues to rotate in the same direction.

In-text Questions (Page 236)

Question 1.
Explain different ways to induce current in a coil.
Answer:
Different ways to induce current in a coil are as given below:

• If a magnetic field is changed around a coil then an induced current is set up in the coil. It can be done by taking a bar magnet and bringing it closer to the coil or taking it away from the coil.
• If a coil is moved in a magnetic field, then again an induced current is set up in the coil.
• If a coil is rotated in a uniform magnetic field, it may also produce an induced current in the coil.

In-text Questions (Page 237)

Question 1.
State the principle of an electric generator.
Answer:
An electric generator is based on the principle of electromagnetic induction. When a rectangular coil is rotated in a uniform magnetic field, an induced voltage is generated between the ends of the coil.

Question 2.
Name some sources of direct current.
Answer:
Some sources of direct current are a cell, a battery and a D.C. generator.

Question 3.
Which sources produce alternating current?
Answer:
A.C. generator and invertors (used in house for emergency power supply) produces alternating current.

Question 4.
Choose the correct option.
A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each
(a) two revolutions
(b) one revolution
(c) half revolution
(d) one-fourth revolution
Answer:
(c) When a rectangular coil of copper wire is rotated in a magnetic field, the direction of the induced current changes once in each half revolution.

In-text Questions (Page Page 238)

Question 1.
Name two safety measures commonly used in electric circuits and appliances.
Answer:
Two safety measures are:

1. Use of earth wire and proper earthing.
2. Use of fuse (now-a-days fuse wire is replaced by MCB).

Question 2.
An electric oven of 2 kW power rating is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.
Answer:
Power rating of electric oven P = 2 kW = 2000 W Supply voltage V = 220 V
So, the current drawn by the electric oven I = P/V = 2000 W/220 V = 9A

As the current rating of domestic electric circuit is only 5 A and the oven draws a current 9 A, which is more than the current rating, hence the circuit will be damaged due to overheating/overloading.

Question 3.
What precaution should be taken to avoid the overloading of domestic electric circuits?
Answer:
The precautions that should be taken to avoid the overloading of domestic circuits are as follows:

• Too many appliances should not be connected to a single socket.
• Too many appliances should not be used at the same time.
• Faulty appliances should not be connected in the circuit.
• Fuse should be connected in the circuit.

Bihar Board Class 10 Science Chapter 13 Magnetic Effects of Electric Current Textbook Questions and Answers

Question 1.
Which of the following correctly describes the magnetic field near a long straight wire?
(a) The field consists of straight lines perpendicular to the wire.
(b) The field consists of straight lines parallel to the wire.
(c) The field consists of radial lines originating from the wire.
(d) The field consists of concentric circles centred on the wire.
Answer:
(d) The field consists of concentric circles centred on the wire.

Question 2.
The phenomenon of electromagnetic induction is
(а) the process of charging a body.
(b) the process of generating magnetic field due to a current passing through a coil.
(c) producing induced current in a coil due to relative motion between a magnet and the coil.
(d) the process of rotating a coil of an electric motor.
Answer:
(c) producing induced current in a coil due to relative motion between a magnet and the coil.

Question 3.
The device used for producing electric current is called a
(a) generator
(b) galvanometer
(c) ammeter
(d) motor.
Answer:
(a) generator

Question 4.
The essential difference between an AC generator and a DC generator is that
(a) AC generator has an electromagnet while a DC generator has permanent magnet
(b) DC generator will generate a higher voltage
(c) AC generator will generate a higher voltage
(d) AC generator has slip rings while the DC generator has a commutator.
Answer:
(d) AC generator has slip rings while the DC generator has a commutator.

Question 5.
At the time of short circuit, the current in the circuit
(a) reduces substantially
(b) does not change
(c) increases heavily
(d) vary continuously.
Answer:
(c) increases heavily

Question 6.
State whether the following statements are true or false.
(а) An electric motor converts mechanical energy into electrical energy.
(b) An electric generator works on the principle of electromagnetic induction.
(c) The field at the centre of a long circular coil carrying current will be parallel straight lines.
(d) A wire with a green insulation is usually the live wire of an electric supply.
Answer:
(a) False
(b) True
(c) True
(d) False.

Question 7.
List two methods of producing magnetic fields.
Answer:

1. Passing electric current through a straight conductor
2. Passing electric current through a circular loop
3. Passing electric current through a solenoid

Question 8.
How does a solenoid behave like a magnet? Can you determine the north and south poles of a current-carrying solenoid with the help of a bar magnet? Explain.
Answer:
The pattern of the magnetic field around a current-carrying solenoid is same as that of a bar magnet. Yes, we can determine the poles of a solenoid by placing a bar magnet near it.

If north pole is placed near side B and repulsion is felt them B is North pole and vice versa.

Question 9.
When is the force experienced by a current-carrying conductor placed in a magnetic field largest?
Answer:
When the direction of current is perpendicular to the direction of magnetic field in a current-carrying conductor.

Question 10.
Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?
Answer:
The direction of current (I) is opposite to the direction of the electron beam. Since the electron beam is deflected to the right side, applying, Fleming’s left hand rule, it is found that the direction of the magnetic field is vertically downwards.

Question 11.
Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of a spilt ring in an electric motor?
Answer:
An electric motor is a rotating device that converts electrical energy to mechanical energy.
Principle: It works on the principle that when electric current is passed through a conductor placed perpendicularly in a magnetic field, a force acts on it as a result of which the conductor begins to move. An electrical motor, is shown in the figure given on the next page.

Current in the coil ABCD enters from the source battery through conducting brush X and flows back to the battery through brush Y. The current in the arm AB of the coil flows from A to B. In arm CD it flows from C to D, that is, opposite to that through arm AB. On applying Fleming’s left hand rule for the direction of force on a current-carrying conductor in a magnetic field, we find that the force acting on arm AB pushes it downwards while the force acting on arm CD pushes it upwards. Thus the coil and the axle O rotate anti-clockwise. At half rotation, Q makes contact with the brush X and P with brush Y. Therefore the current in the coil gets reversed and flows along the path DCBA. The reversal of current also reverses the direction of force acting on the two arms AB and CD. Thus the arm AB of the coil that was earlier pushed down is now pushed up and the arm CD previously pushed up is now pushed down. Therefore the coil and the axle rotate half a turn more in the same direction. The reversing of the current is repeated at each half rotation, giving rise to a continuous rotation of the coil and to the axle.
The split ring reverses the direction of flow of current in an electric motor.

Question 12.
Name some devices in which electric motors are used.
Answer:
Electric fans, refrigerators, mixers, washing machines, computers and CD players.

Question 13.
A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (i) pushed into the coil, (ii) withdrawn from inside the coil, (iii) held stationary inside the coil?
Answer:
(i) The needle of the galvanometers moves momentarily in one direction
(ii) The needle of the galvanometers moves momentarily but in the opposite direction to (i)
(iii) No deflection of needle.

Question 14.
Two circular coils A and B are placed closed to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason.
Answer:
By changing current in the coil A, a current will be induced in coil B. This is because magnetic field associated with A changes when current in coil A is changed. This changes the magnetic field lines associated with coil B and thus a current is induced in it.

Question 15.
State the rule to determine the direction of a (i) magnetic field produced around a straight conductor-carrying current, (ii) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it, and (iii) current induced in a coil due to its rotation in a magnetic field.
Answer:
(i) Imagine that you are holding a current-carrying straight conductor in your right hand such that thumb points towards the direction of current, then your fingers will wrap around the conductor in the direction of the field lines of the magnetic field, as shown in the figure. This is known as the right hand thumb rule.

(ii) Fleming’s left-hand rule determines the force on a conductor: According to this rule, stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular.

If the fore-finger points in the direction of the magnetic field and the middle-finger in the direction of current, then the thumb will point in the direction of motion or force acting on the conductor.

(iii) Fleming’s right hand rule determines the direction of the induced current: Stretch the thumb, forefinger and middle finger of the right hand so that they are perpendicular to each other, as shown in figure. If the forefinger indicates the direction of the magnetic field and the thumb shows the direction of motion of the conductor, then the middle finger will show the direction of induced current. This simple rule is called Fleming’s right-hand rule.

Question 16.
Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?
Answer:
In an electric generator, mechanical energy is used to rotate a conductor in a magnetic field to produce electricity.
Principle: It works on the principle that when magnetic lines of force linked with a coil changes, a current is induced in the coil.

An electric generator is shown in the figure below.

When the coil ABCD is rotated clockwise, by applying Fleming’s right-hand rule, induced currents are set up in the these arms along the directions AB and CD. Thus an induced current flows in the direction ABCD. If there are larger number of turns in the coil, the current generated in each turn adds up to give a large current through the coil.

After half a rotation, arm CD starts moving up and AB moving down. As a result, the direction of the induced currents in both the arms change, giving rise to the net induced current in the direction DCBA. The current in the external circuit now flows from B₁ and B₂. Thus after every half rotation the polarity of the currnet in the respective arms changes. Such a current, which changes direction after equal intervals of time, is called an alternating current (abbreviated as AC). This device is called an AC generator.

The function of the brushes is to make contact with the rotating rings and through them supply current to the external circuit.

Question 17.
When does an electric short circuit occur?
Answer:
Electric short-circuit occurs when live wire comes in direct contact with the neutral wire due to some fault in an appliance or damaged insulation of the wires.

Question 18.
What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Answer:
It is used as a safety measure to ensure that any leakage of current to a metallic body does not give severe shock to the user.

Earth wire provides a low resistance conducting path for electric current to the earth which may have leaked from an appliance.

Bihar Board Class 10 Science Chapter 13 Magnetic Effects of Electric Current Textbook Activities

Activity 13.1 (NCERT Textbook Page 223)

Discussion and conclusion:
The needle of the compass is deflected when electric current is passed through it since electric current produces a magnetic field.

Activity 13.2 (NCERT Textbook Page 224)

Discussion and conclusion:
The iron filings arrange themselves in a pattern. The magnet exerts its influence in the region surrounding it. This region surrounding the magnet is called magnetic field.

Activity 13.4 (NCERT Textbook Page 226)

Discussion and conclusion:
The direction of magnetic field due to a current carrying straight conductor depends upon the direction of current flowing through it. If we reverse the direction of current the direction of magnetic field is also reversed.

Activity 13.7 (NCERT Textbook Page 230)

Discussion and conclusion:
Current carrying wire placed in magnetic field experience force. On reversing the direction of current, the direction of force is reversed.

Activity 13.8 (NCERT Textbook Page 233-234)

Discussion and conclusion:

• An emf and current is induced in the circuit when magnetic field linked with the coil changes.
• When the magnet is stationary, magnetic field linked with the coil does not change. Hence there is no induced emf and current in the coil.
• The direction of induced current depends on the direction of motion of the magnet.

Activity 13.9 (NCERT Textbook Page 235)

Discussion and conclusion:

• Whenever electric current through coil-1 is changed (either increased or decreased), a pd is induced in coil-2.
• The coil-1 (containing battery) is called the primary coil whereas coil-2 is called the secondary coil.
• The induced pd in coil-2 is due to change in magnetic field lines in it which in turn is due to change in magnetic field lines in coil-1 through which current is changed.