An incandescent light bulb is advertised as “60W at 120V.” When the filament reaches its normal operating temperature, its resistance is much higher than when it is cold. For a particular bulb, the hot-to-cold resistance ratio is observed to be 11:1. Assume the filament behaves ohmically at both temperatures.
(a) Using the rating information, calculate the filament’s resistance when the bulb has reached its normal operating temperature.
(b) Determine the cold resistance of the filament immediately before the bulb is switched on.
(c) Just after the switch is closed, while the filament is still cold, find the current that initially flows through the bulb.
(d) Compute the initial electrical power dissipated in the filament and compare it with the rated operating power. Explain briefly why the filament is not damaged even though the initial power is substantially different from the rated value.