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 locations after a sufficiently long time of operation due to non-uniform evaporation of tungsten from the filament. If the bulb is powered at constant voltage, which of the following statements(s) is(are) true.

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The temperature distribution over the filament is uniform.

The resistance over small sections of the filament decreases with time

The filament emits more light at higher band of frequencies before it breaks up

The filament consumes less electrical power towards the end of the life of the bulb.

answer is C.

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Detailed Solution

Concept: Filaments break up energy consumed by the filament is highest and more band of frequencies emitted.
The filament will get thinner as it nears its end of life. There will be more resistance, which means less power will be spent and less light will be emitted. The distribution of temperature will not be uniform. The filament will snap at the temperature's highest point. By becoming flat, the black body radiation curve causes the filament to use less electricity as the bulb nears its end of life.
Hence, the correct option is 3,4.

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