A tungsten filament bulb is connected to a variable voltage supply. The potential difference, V, is varied and the current, I and steady temperature T of the filament is recorded. A graph is plotted for ln(VI) Vs ln(T). Find the slope of the graph. Assume that temperature of filament T >> T₀ = atmospheric temperature.

Question

G1 Physics · Accepted Answer

Image At steady high temperature, electrical power V²/R is balanced mainly by radiation ∝ T⁴. For a filament with resistance approximately proportional to T over the considered range, ln(V/I)=lnR varies approximately linearly with lnT with slope 4. Thus the slope is 4.