Lakhmir Singh & Manjit Kaur: Electricity, Solutions- 1 | Science Class 10 PDF Download

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Question 1:
By what other name is the unit joule/coulomb called ?
Solution :
Volt

Question 2:
Which of the following statements correctly defines a volt ?
(a) a volt is a joule per ampere.
(b) a volt is a joule per coulomb.
Solution :
(b) a volt is a joule per coulomb.

Question 3:
(a) What do the letters p.d. stand for ?
(b) Which device is used to measure p.d. ?
Solution :
(a) p.d. stands for potential difference.
(b) Voltmeter is used to measure p.d.

Question 4:
What is meant by saying that the electric potential at a point is 1 volt ?
Solution :
Electric potential at a point is 1 volt means 1 joule of work is done in moving 1 unit positive charge from infinity to that point.

Question 5:
How much work is done when one coulomb charge moves against a potential difference of 1 volt ?
Solution :
Potential difference = 1 V
Charge moved = 1C
Work done = Potential difference x Charge moved
= 1 x 1 = 1 J

Question 6:
What is the SI unit of potential difference ?
Solution :
Volt

Question 7:
How much work is done in moving a charge of 2 C across two points having a potential difference of 12 V ?
Solution :
Given,
Potential difference = 12 V,Charge moved = 2 C
We know that,
Work done= p.d. x charge moved
= 12 x 2
= 24 joules.

Question 8:
What is the unit of electric charge ?
Solution :
Coulomb

Question 9:
Define one coulomb charge.
Solution :
One coulomb of charge is that quantity of charge which exerts a force of 9 × 109 Newton on an equal charge is placed at a distance of 1 m from it.

Question 10:
Fill in the following blanks with suitable words :
(a) Potential difference is measured in………….. by using a……………. placed in………… across a component.
(b) Copper is a good………….. Plastic is an……………
Solution :
(a) volts; voltmeter; parallel
(b) conductor; insulator

Question 11:
What is meant by conductors and insulators ? Give two examples of conductors and two of insulators.
Solution :
Conductors:- Those substances through which electricity can flow are known as conductors. E.g., Copper, silver etc.
Insulators:- Those substances through which electricity cannot flow are known as insulators. E.g., Plastic, cotton etc.

Question 12:
Which of the following are conductors and which are insulators ?
Sulphur, Silver, Copper, Cotton, Aluminium, Air, Nichrome, Graphite, Paper, Porcelain, Mercury, Mica, Bakelite, Polythene, Manganin.
Solution :
Conductor:- Silver, Copper, Aluminum, Nichrome, Graphite, Mercury, Manganin
Insulators:- Sulphur, Cotton, Air, Paper, Porcelain, Mica, Bakelite, Polythene

Question 13:
What do you understand by the term “electric potential” ? (or potential) at a point ? What is the unit of electric potential ?
Solution :
The electric potential (or potential) at a point in an electric field is defined as the work done in moving a unit positive charge from infinity to that point.
Unit of electric potential is volt.

Question 14:
(a) State the relation between potential difference, work done and charge moved.
(b) Calculate the work done in moving a charge of 4 coulombs from a point at 220 volts to another point at 230 volts.
Solution :
(a) Potential difference = Work done/Charge moved.
(b) V1=220 V, V2=230V, Charge moved=4C
Thus, the potential difference= V2- V1 =230-220
=10.
We know that,
Work done = Potential difference x Charge moved
= 10 x 4
Work done = 40 joules

Question 15:
(a) Name a device that helps to measure the potential difference across a conductor.
(b) How much energy is transferred by a 12 V power supply to each coulomb of charge which it moves around a circuit ?
Solution :
(a) Voltmeter
(b) Given : Potential difference = 12V, Charge moved=1C
We know that,
Work done = Potential difference x charge moved
= 12 x 1 = 12 joules
Since work done on each coulomb of charge is 12 joules, the energy given to each coulomb of charge is also 12 joules.

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Question 16:
(a) What do you understand by the term “potential difference” ?
(b) What is meant by saying that the potential difference between two points is 1 volt ?
(c) What is the potential difference between the terminals of a battery if 250 joules of work is required to transfer 20 coulombs of charge from one terminal of battery to the other ?
(d) What is a voltmeter ? How is a voltmeter connected in the circuit to measure the potential difference between two points. Explain with the help of a diagram.
(e) State whether a voltmeter has a high resistance or a low resistance. Give reason for your answer.
Solution :
(a) Potential difference between two points in an electric circuit is defined as the amount of work done in moving a unit charge from one
point to the other point.
(b) The potential difference between two points is 1 volt means 1 joule of work is done in moving 1 coulomb of electric charge from one point to the other.
(c) Given: Work done = 250J, Charge moved = 20C.
we know that,Potential difference = Work done/Charge moved
= 250/20 = 12.5
(d) A voltmeter is a device which is used to measure the potential difference between two points in an electric circuit. Voltmeter is always connected in parallel across the two points where the potential difference is to be measured.

(e) Voltmeter has a high resistance so that it takes a negligible current from the circuit.

Question 22:
Three 2 V cells are connected in series and used as a battery in a circuit.
 (a) What is the p.d. at the terminals of the battery ?
 (b) How many joules of electrical energy does 1 C gain on passing through (i) one cell (ii) all three cells ?
Solution :
(a) If three cells of 2 volt each are connected in series to make a battery, then the total potential difference between terminals of the battery will be 6V.
(b) (i) Given: p.d. = 2V, Charge moved = 1C
We know that
Work done = p.d. x charge moved
= 2 x 1
Work done = 2 joules
(ii) Given: p.d. = 6V, Charge moved = 1C
Work done = p.d. x charge moved
= 6 x1
Work done = 6 joule.

Question 23:
The atoms of copper contain electrons and the atoms of rubber also contain electrons. Then why does copper conduct electricity but rubber does not conduct electricity ?
Solution :
Copper has free electrons that are loosely held by the nuclei of the atoms. These free electrons result in conduction of electricity.
The electrons present in rubber are strongly held by the nuclei of its atoms. So, rubber does not have free electrons to conduct electricity.