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

Dust inside the bulb condenses on the top
The heat of the bulb scorches the glass at the top
The tungsten filament evaporates and collects there
Glass undergoes a change due to the heat

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Physics
Which of the following options correctly explains the term heat budget?

It is the amount of heat which the surface of earth receives from the sun.
It is the radiation from the earth in the form of long waves.
It is a mode of transfer of heat through matter by molecular activity.
It is the balance between incoming and outgoing radiation

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Physics
In a conductor

The forbidden energy gap is very wide
There is no conduction band
The valence band and the conduction band overlap each other
The forbidden energy gap is very narrow

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