posted by JOTHEY .
A 40 W (120V) light bulb has a tungsten filament of thickness 0.035 mm. The filament's operating temperature is 1500 degrees C.
How long is the filament?
What is the resistance of the filament at 20 degrees C?
look up the resisitive of tungsten at 1500C. you know area, compute length from known resistance (Power=V^2/R)
(5.0x10^7) is the reisisttivity of tugsten at 1500 degrees