# Current Electricity

Max. Marks :: 30 Time:: 75 minutes

**1 mark questions**

- 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?
- Define internal resistance.
- 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.
- Define mobility.
- State Ohm’s law.
- State the principle of a potentiometer.
- Write the colour coding of a carbon resistor of resistance 18000 Ω and a tolerance 10%
- What is a thermistor?
**2 Marks Questions** - Deduce Ohm’s law using the concept of drift velocity.
- State Kirchhoff’s laws for electric networks.
- Distinguish emf and terminal voltage.
- Derive an expression for drift velocity.
**3 marks questions** - 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.
- 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.
- Draw the diagram showing the experimental arrangement for determining the resistance of a given wire of unknown resistance.
**5 Marks Questions** - (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

## 1 ping

[…] Current Electricity : Physics Revision Test for Class XII […]