Question

The surface of the electric bulb with a tungsten filament becomes greyish black after used for long time ?

Answer 1

Answer:

Just because of the uniform deposition of tungsten on the inner wall of light bulb, gray spots are developed against its walls after long use.

Explanation:

There are many possibilities for a light bulb to have gray spots on its inner wall. However, the gray spot is developed because of the evaporation of Tungsten. If the bulb is filled with inert gas there are many possibilities for the bulb to have some moisture in it. Tungsten tri-oxide is formed as a result of Tungsten’s reaction with that moisture. The oxide will deposit on the inner wall of the bulb and forms Gray Spots.