− Ιf the multi meter reads 1, or displays OL, it’s overloaded. You will need to try a higher mode such as 200K Ω or 2M Ω etc.

− If the multi meter reads 0.00 or nearly 0, then you need to lower the mode to 2K Ω or 200 Ω.

Note the value of resistance in your note book. Connect a circuit with components as shown in fig.- 13. Switch on the circuit. After few minutes, measure the resistance of the bulb again as explained above. Note this value in your note book. What difference do you notice between these two readings? The value of resistance of the bulb in second instance is more than the resistance of the bulb in open circuit.

• What could be the reason for increase in the resistance of the bulb when current flows through it?

You will notice that the bulb gets heated. The increase in temperature of the filament in the bulb is responsible for increase in resistance of the bulb. Hence we can conclude that there is a relation between resistance of the bulb and its temperature.

    Thus the value of resistance of a conductor depends on temperature and increases with rise in temperature.

Nature of material and resistance



Collect different metal rods of the same length and same cross sectional area like copper, aluminium, iron etc. Make a circuit as shown in fig.- 14. P and Q are the free ends of the conducting wires. Connect one of the metal rods between the ends P and Q. Switch on the circuit. Measure the electric current using the ammeter connected to the circuit and note it in your notebook. Repeat this with other metal rods and measure electric currents in each case. What do you notice? The values of current are different for different metal rods for a constant potential difference.

    From this activity, we conclude that the resistance of a conductor depends on the material of the conductor.

• What happens to the resistance of a conductor if we increase its length?