## Saturday, July 17, 2010

### Electricity Practice Questions for CBSE

1. Define electric potential difference?

2. Why is an ammeter connected in series in a circuit?

3. Why is a voltmeter connected in parallel in a circuit?

4. State the law that governs the strength of the current passing through a metallic conductor when a p.d is applied across its end. Illustrate this law graphically?

5. State the law which governs the amount of heat produced in a metallic conductor when current is passed through it for a given time. Express this law mathematically?

6. Define resistance. What are the factors on which it depends?

7. A copper wire of resitivity P is stretched to reduce its diameter to half its previous value. What is the new resistivity?

8. Define the S I unit of electric current and potential difference.

9. Derive expressions for equivalent resistance of resistors connected in

a. series combination

b. parallel combination

10. What is an electric fuse? Explain its function.

11. Explain, how the heating effect of electric current is made use in the functioning of an electric bulb?

12. State the relation between the commercial and SI unit of electric energy.

13. Write the advantages of connecting electrical appliances in parallel and disadvantages of connecting them in series in a household circuit.

14. Why is tungsten used almost exclusively for making the filaments of electric lamps?

15. A piece of wire is redrawn by pulling it until its length is doubled .Compare the new resistance with the original value.

16. An electric geyser has rating 2000 w, 220 v marked on it. What should be the minimum rating in whole number of a fuse wire that may be required for safe use with the geyser?

17. Three resistors each of resistance 10 ohm are connected, in turn, to obtain a. minimum resistance b. Maximum resistance. Compute

a) The effective resistance in each case

b) The ratio of minimum to maximum resistance so obtained.

18. Two resistors of resistance 2 ohms and 4 ohms are, in turn connected

a) In series

b) In parallel to a given battery for same interval.

Compute the ratio of the total quantity of heat produced in the combination in the two cases.

19. Two metallic wires A and B are connected in parallel. Wire A has length L and radius R wire B has a length 2L and radius 2r. Compute the ratio of the total resistance of parallel combination and resistance of wire A.

20. In a house three bulb of 100w each are lighted for 4 hours daily and six tube lights of 20w each are lighted for 5 hours daily and a refrigerator of 400w is worked for 10 hours daily for a month of 30 days. Calculate the electricity bill if the cost of one unit is Rs 4.00.

21. Three resistors of 4ohms, 6ohms and 12 ohms are connected in parallel. The combination of above resistors is connected in series to a resistance of 2 ohms and then to a battery of 6 volts. Draw a circuit diagram and calculate

a) Current in main circuit

b) Current flowing through each of the resistors in parallel

c) P.d and the power used by the 2 ohm resistor.

22. Two lamps, one rated 100 W at 220 V and the other 60W at 220 V, are connected in Parallel to a 220 volt supply. What current is drawn from the supply line?

1. 2. 