After long periods of use a grey spot develops on the...

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After long periods of use, a grey spot develops on the inside of a bulb. This is because

A. The tungsten filament evaporates and collects there

B. The heat of the bulb scorches the glass at the top

C. Dust inside the bulb condenses on the top

D. Glass undergoes a change due to the heat

Answer: Option C

Solution (By Examveda Team)

At high operating temperatures, tungsten evaporates from the filament and gradually forms a gray film on the inside of the bulb. The inert gas atoms collide with the evaporating tungsten, causing some of the tungsten atoms to return to the filament.

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