Question

A common flashlight bulb is rated at 0.23 a and 2.9 v (the values of the current and voltage under operating conditions). if the resistance of the bulb filament at room temperature (20°c) is 1.1 ω, what is the temperature of the filament when the bulb is on? the temperature coefficient of resistivity is 4.3 × 10-3 k-1 for the filament material.

Answer 1

The resistance at operating temperature is R = V/I = 2.9 V / 0.23A = 12.61 ohmsT from R – R0 = Roalpha (T – T0), we find that:T = T0 + 1/alpha (R/R0 -1) = 20 degrees Celsius + (1/ 4.3 x 10^-3/K) (12.61 ohms/ 1.1 ohms – 1)T = 2453.40 degrees Celsius