TEACHING PHYSICS: Switching time of a 100 watt bulb

The switching time of a bulb, i.e. the time taken to achieve a state of full brilliance after being turned on, is of considerable pedagogical interest. To estimate this time we take the resistance and heat capacity of the filament as suitably parametrized functions of the temperature and solve a simplified heat equation. A numerical comparison is made with the experimental data on a 100 watt bulb.