Question

A 100 W bulb has tungsten filament of total length 1.0 m and radius 4 × 10−5 m. The emissivity of the filament is 0.8 and σ = 6.0 × 10−8 W m−2K4. Calculate the temperature of the filament when the bulb is operating at correct wattage.

Answer 1

The temperature is 1700 K.

Explanation:

• Q/t =  AeσT4  

• => T4 = θ/teAσ  

• => T = 1697.0, which is approximately 1700K.

• A material’s emissivity of the surface is the effectiveness of the material’s emitting energy similar to that of thermal radiation. It is to be noted that the electromagnetic radiation is the thermal radiation, which might include both infrared radiation and visible radiation. This is not visible to the eyes of the humans.