How does the filament of a lightbulb glow?

Question

How does the filament of a lightbulb glow? Doesn't it have like a closed circuit or something??

Answer 1

You put a current through the filament. The electrons are slowed by the resistance of the filament and give up some of their power to the filament. The filament gets hot. It glows due to the heat. This is called black body radiation.

Answer 2

The current flowing through the filament gets heated due to its resistance and this can be calculated by I squared R where I is the current and R is the resistance.

At high temperature, the filament emits radiation and we gets light.