**Extra Questions for Class 10 Science Chapter 12 Electricity**

**Q.1. Name a device that helps to maintain a potential difference across a conductor.**

Answer. Cell or battery

**Q.2. Define 1 volt. Express it in terms of SI unit of work and charge calculate the amount of energy consumed in carrying a charge of 1 coulomb through a battery of 3 V.**

Answer. When 1 joule of work is done in carrying 1 coulomb of charge, from infinity to a point

in the electric field, then potential at that point is called 1 volt. Potential difference between two

points is

**Q.3. Write S.I. unit of resistivity.**

Answer. Ohm-metre (Ωm).

**Q.4. How is an ammeter connected in a circuit to measure current flowing through it?**

Answer. In series

**Q.5. What happens to resistance of a conductor when its area of cross-section is increased?**

Answer. Decreases

**Q.6. Name the physical quantity which is (i) same (ii) different in all the bulbs when three bulbs of:**

(a) same wattage are connected in series.

(b) same wattage are connected in parallel.

(c) different wattage are connected in series.

(d) different wattage are connected in parallel.

Answer. (a) For identical bulbs in series- same current, same potential difference.

(b) For identical bulbs in parallel- same potential difference, different current.

(c) For unidentical bulbs in series- same current, different potential difference.

(d) For unidentical bulbs in parallel- different current, same potential difference.

**Q.7. A given length of a wire is doubled on itself and this process is repeated once again. By what factor does the resistance of the wire change?**

Answer. Am. Length becomes one-fourth of the original length and area of cross-section

becomes four times that of original.

So, new resistance is (1/16)th of original resistance.

**Q.8. What is an electric circuit? Distinguish between an open and a closed circuit.**

Answer. An arrangement for maintaining the continuous flow of electric current by the electrical

energy source through the various electrical components connected with each other by conducting wires is termed as electric circuit.

An open circuit does not carry any current, while a closed circuit carries current.

**Q.9. (a) Define the term ‘volt’.(b) State the relation between work, charge and potential difference for an electric circuit.Calculate the potential difference between the two terminals of a battery if 100 J of work is required to transfer 20 C of charge from one terminal of the battery to the other.**

Answer.

(a) When 1 joule of work is done in carrying 1 coulomb of charge, from infinity to a point in the

electric field, then potential at that point is called 1 volt.

(b) Potential difference, V = Work done on unit charge =W/q

Work is 100 J,q=20C

Potential difference,V=W/q=100/20=5V

**Q.10. A 9Ω resistance is cut into three equal parts and connected in parallel. Find the equivalent resistance of the combination.**

Answer.

**Q.11. (a) Define the term ‘coulomb’.(b) State the relationship between the electric current, the charge moving through a**

**conductor and the time of flow.**

Calculate the charge passing through an electric bulb in 20 minutes if the value of current is 200 mA.

Calculate the charge passing through an electric bulb in 20 minutes if the value of current is 200 mA.

Answer.

(a) When 1 A current flows across the wire in 1 second, the charge transfer across its ends is said

to be 1 coulomb.

(b) The relationship between the electric current I, the charge q and time t is

**Q.12. (a) How is the direction of electric current related to the direction of flow of electrons in a wire?(b) Calculate the current in a circuit if 500 C of charge passes through it in 10 minutes.**

Answer.

(a) Conventional direction of electric current is opposite to the direction of flow of electrons in a

wire.

(b) q = 500 C, t = 10 X 60 = 600 s

I = 500/600 = 5/6A

**Q.13. An electric iron has a rating of 750 W, 220 V. Calculate the (i) current flowing through it,and (ii) its resistance when in use.**

Answer. Given: P = 750 W, V = 220 V

(i) P = VI

**Q.14. Study the following electric circuit and find (i) the current flowing in the circuit and (ii) the** **potential difference across 10 Ω resistor.**

Answer.

Q.15. What is meant by electric current? Name and define its SI unit. In a conductor electrons are

flowing from B to A. What is the direction of conventional current? Give justification for your answer. A steady current of 1 ampere flows through a conductor. Calculate the number of electrons that flows through any section of the conductor in 1 second. (Charge on electron 1.6 X 10^{-19} coulomb).

Answer.

>>Electric Current: The amount of charge ‘Q’ flowing through a particular area of cross section

in unit time ‘t’ is called electric current, i.e.

>>Electric current, I = Q/t

>> SI unit of electric current is ampere.

>> One ampere of current is that current which flow when one coulomb of electric charge

flowing through a particular area of cross-section of the conductor in one second, i.e. 1A = 1

Cs^{-1}.

>> The direction of conventional current is A to B, i.e. opposite to the direction of flow of electrons. In a metal, flow of electrons carrying negative charge constitutes the current.

Direction of flow of electrons gives the direction of electronic current by convention, the direction of flow of positive charge is taken as the direction of conventional current.**Charge = q = ne**

Q.16. What is meant by electrical resistivity of a material? Derive its S.I. unit.

Answer. Mathematically, resistivity of the conducting material is given by

ρ = R x A/L

If L = 1 m, A = 1 m^{2}, then ρ = R

Hence, the resistivity of the material is defined as the resistance offered by a metallic wire having

a unit length and a unit area of cross-section. Since unit length and unit area of cross-section forms a cube, the specific resistance or resistivity can also be defined as the resistance offered by

a cube of a material of side 1 m when current flows perpendicularly through the opposite faces. In SI system, its units is

Q.17. (a) Write two points of difference between electric energy and electric power. (6) Out of 60

W and 40 W lamps, which one has higher electrical resistance when in use.

(c) What is the commercial unit of electric energy? Convert it into joules.

Answer. (a) Difference between electric energy and electric power:

i.e. less the power of electrical device, higher is its electrical resistance.

(c) Kilowatt hour – Commercial unit of electrical energy

1 kWh = 1000 Wh = 1000 J/S x 3600 sec

= 3600000 J = 3.6 x10^{6}J

**Q.18. State Ohm’s law. Write the necessary conditions for its validity. What will be the nature of graph between potential difference and current for a conductor? Name the physical quantity that can be obtained from this graph.**

Answer:

Ohm’s law : When the physical conditions such as temperature etc. remain same, the

current flowing through the conductor is directly proportional to the potential difference applied

across the ends of the conductor, i.e.,

Necessary condition for validity of Ohm’s law is that physical condition such as

temperature of the conductor remains same.

Ohm’s law does not hold under all conditions. Ohm’s law does not hold for non-ohmic material

such as electrotyte.