# Frank Solutions for Chapter 8 Electricity and Magnetism- Current Electricity Class 9 Physics ICSE

1. What do you mean by an electric current?

The flow of electrons in a particular direction in a conductor is called an electric current.

2. What is an electric cell?

An electric cell is the source of electric current in which chemical energy changes to electrical energy.

3. How much is the charge on an electron?

The charge on an electron is -1.6×10-19 C.

4. Name the constituents of a cell.

The constituents of cell are two electrodes in the form of conducting rods immersed in the solution called electrolyte.

5. Write SI units of

(i) Electric current,

(ii) Potential difference,

(iii) Resistance.

(i) S.I. unit of electric current is Ampere

(ii) S.I unit of potential difference is volt.

(iii) S.I unit of resistance is ohm.

6. What is the number of electrons that would flow per second through the cross-section of a wire when 1 A current flows in it?

I = 1 A

T = 1s.

I = Q/t = ne/t

So, n = I× t/e = 1×(1/1.6 ×10-19) = 6.25×1018 electrons.

7. 0.7 C charges passes through a cross-section of a conductor in 7s. Find the current.

I = Q/t = 0.7/7 = 0.1 Ampere.

8. Name the instrument used to control current in an electric circuit.

Rheostat is used to control the current in the circuit.

9. What is the other name of a variable resistor?

Rheostat is the variable name of electrical resistance.

10. What is the function of a switch in an electric circuit?

Switch is used to put the current on and off in the circuit.

11. Write symbols and state functions of each of the following components in an electric circuit:

(i) Cell

(ii) ammeter

(iii) voltmeter

(iv) key

(v) battery

(vi) rheostat

(i) Cell - Cell provide an electric current in the circuit.

(ii) Ammeter - It is a device to measure an electric current in the circuit.
(iii) Voltmeter - It is used to measure the potential difference between two points in the circuit.
(iv) Key - It is used to put the current on and off in the circuit.
(v) Battery - It is used to charge the cell.
(vi) Rheostat – It is used to control the electric current in the circuit.

12. A current of 1.2 A flows through a conductor for 3.0 s. What amount of charge passes through the conductor?

I = Q/t

So, Q = I,

t = 1.2 ×3.0 = 3.6 C

13. In fig. 16, label the different parts A, B, C, D, E and F. State the functions of each part. Show in the diagram the direction of flow of current.

A - is a voltmeter to measure the potential difference, B is an electric resistance to control the current in the circuit, C is the ammeter to measure the magnitude of an electric current, D is cell to provide electric current in circuit, E is an electric key to on and off the circuit, F is the rheostat to control the current in circuit.

14. In fig. 17, I-V graph is shown for a good conductor. What does the slope of the graph represent ?

The slope of the graph represents that with current flowing through a conductor is directly proportional to the potential difference applied the resistance of conductor is constant.

15. What do you mean by the potential difference? Write its SI unit.

Potential difference between two conductors is defined as the amount of work done in moving the unit positive charge from one conductor to another through the wire.

16. Is electric current a scalar quantity?

Yes, electric current is a scalar quantity.

17. State the factors on which the electrical resistance of a wire depends.

The electric resistance of the wire depends on the following factors :

1. The length of the wire.
2. The area of cross-section of the wire.
3. The temperature of the wire.
4. The material of the wire.

18. What is the SI unit of resistance?

The S.I unit of resistance is ohm.

19. A bulb is connected to a cell. How is the resistance of circuit affected if another identical bulb is connected (i) in series, (ii) in parallel, with the first bulb?

If another bulb is connected in series then the resistance of the wire will increase.

If another bulb is connected in parallel then resistance will decrease.

20. How are the potential difference (V), current (I) and resistance (R) related?

V = IR

21. ‘The resistance of a wire is 2 ohm’. Explain the meaning of this statement.

The resistance of the wire is 2 ohms if a current of 1 ampere flows through it when the potential difference across it is 2 volt.

22. (i) Cell – Cell provide an electric current in the circuit.

(ii) Ammeter – It is a device to measure an electric current in the circuit.

(iii) Voltmeter – It is used to measure the potential difference between two points in the circuit.

(iv) Key – It is used to put the current on and off in the circuit.

(v) Battery – It is used to charge the cell.

(vi) Rheostat – It is used to control the electric current in the circuit.

The current I = V/R = 14/28 = 0.5 Ampere.

23. State three factors on which the resistance of a wire depends. Explain, how does the resistance depend on the factors stated by you.

The factors on which resistance of the wire depends are:

1. The length of the wire, resistance is directly proportional to the length of wire.
2. The cross-section of the wire, resistance is inversely proportional to the cross-section of the wire.
3. The temperature of the wire, resistance of wire is directly proportional to the temperature of the wire.
4. The material of the wire (good conductors possess less resistance.)

24. What amount of work is required in moving 3 C charge through a potential difference of 6 V?

W = V.Q = 6.3 = 18 Joule.

25. What is the physical meaning of resistance?