# Current Electricity

Max. Marks :: 30 Time:: 75 minutes

1 mark questions

1. The drift velocity is of the order of a few cm/s. But when we switch on a bulb, it glows instantly. How is this possible?

2. Define internal resistance.

3. If n identical resistors are connected in series first and then in parallel, Calculate the ratio of effective resistance in series to the effective resistance in parallel.

4. Define mobility.

5. State Ohm's law.

6. State the principle of a potentiometer.

7. Write the colour coding of a carbon resistor of resistance 18000 Ω and a tolerance 10%

8. What is a thermistor?

2 Marks Questions

9. Deduce Ohm's law using the concept of drift velocity.

10. State Kirchhoff's laws for electric networks.

11. Distinguish emf and terminal voltage.

12. Derive an expression for drift velocity.

3 marks questions

13. A battery om emf E and internal resistance r gives a current 0.5 A with an external resistance of 12 Ω and a current 0.25 A with an external resistance of 25Ω. Calculate the internal resistance and emf of the cell.

14. An electric motor operating on a 50 V dc supply draws a current of 12A. If the efficiency of the motor is 30%, estimate the resistance of the windings of the motor.

15. Draw the diagram showing the experimental arrangement for determining the resistance of a given wire of unknown resistance.

5 Marks Questions

16. (a)Explain how a potentiometer is used to determine the internal resistance of a primary cell.

(b)State the factors affecting the internal resistance of a cell