Question

Why does an electric light bulb nearly always burn out just as you turn on the light, almost never while the light is shining?

Short answer

After turning on the bulb the temperature of the filament goes to very high at an instance. This causes the filament to expand.

The filament weakens by the time. Thus the expansion of filament and increasing temperature causes the bulb to burn out

Step-by-step solution

Filament in a bulb

The word filament refers to the wire or thread that lights up within the bulb when it is switched on.

Tungsten is used as filament in an electric bulb.

Understand the use of a filament in a bulb

After turning on the bulb the temperature of the filament goes to very high at an instance. This causes the filament to expand.

The filament weakens over time. Thus the expansion of filament and increasing temperature causes the bulb to burn out.