An incandescent bulb has a thin filament of tungsten that is heated to high temperature by passing an electric current. The hot filament emits black - body radiation. The filament is observed to break up at random to break up at random locations after a sufficiently long time of operation due to non-uniform evaporation of tungsten from the fialment. If the bulb is powered at constant voltage, which of the following statement (s) is (are) true?

Options

A. The temperature distribution over the filament is uniform
B. The resistance over small sections of the filament decreases with time
C. The filament emits more light at higher band of frequencies before it breaks up
D. The filament consumers less electrical power towards the end of the life of the bulb.

Answer

C, D

Explanation

(c,d)
With the use of filament and the evaporation involved, the filament will become thinner thereby decreasing the area of cross-section and increasing the resistance. Therefore the filament will consume less power towards the end of life. As the evaporation is non-uniform, the area of cross-section will be different at different cross-section . Therefore temperature distribution will be non-uniform. The filament will break at the point where the is temperature is maximum. When the filament temperature is higher `(lambda_n prop 1/T)`, it emits light of lower wavelength or higher band of frequencies.