The fi lament of an incandescent lightbulb is a thin tungsten wire. Suppose a lightbulb has a resistance of 50 Ω at room temperature. During normal operation, the filament reaches a temperature of about 3000 K.
(a) What is its resistance at that temperature? The temperature coefficient of resistivity for tungsten is α = 4.5 x 10^-3 K^-1.
(b) If the bulb’s brightness depends only on the current, and a larger current gives a greater brightness, will the bulb’s brightness be greater or smaller after it has warmed up?