How does a bulb glow when the switch is turned on?

The bulb glows because the filaments get heated up due to current and lights up. • The bulb work on the principle that when a metal is heated it starts emitting light at some point.is turned on • When the switch is turned, an electric current is passed through • When an electric current is passed through a conductor it generates heat, H = IR2t (Joule's equation), where I is the current, R is the resistance of the conductor and t is the time for which current is passed. • This heat is used by the atomic electrons to get excited to higher energy levels from the ground state. • When these electrons return back to their ground state, a light photon is emitted, and this is how a bulb glows.