Question

Resistance of an incandescent filament of a lamp is comparatively much more than that when it is at room temperature. Why? [HOTS]

Answer 1

Answer:

The resistance of a wire is directly proportional to the length and temperature of the wire while it is inversely proportional to its cross sectional area.

Therefore when temperature of  a wire rises, so does the resistance to the flow of current. The rise in temperature causes a rise in the vibration of the atoms in the filament, increasing the collision between the atoms and the flowing electrons. The increase in collision decreases the rate of flow of electrons and hence increases the resistance. This is the reason for the high resistance in the incandescent bulb when the temperatures are high, more than the resistance when the filament is at room temperature.