Question

when does an electric bulb glow tell me explained ?​

Answer 1

An electric bulb glows when electric current passes through it. In a closed electric circuit, the electric current passes from one terminal of the electric cell to the other terminal. Switch is a simple device that is used to either break the electric circuit or to complete it.

Answer 2

when power supply on then

The filament of an electric bulb glows because of the heating effect of electric current. As the current passes through the bulb it heats the filament which gives off light.