Question

What happen to the bulb when it is in series connection?

Answer 1

If the bulb is in series with something else, then . . .

--  The brightness of the bulb depends on the other device in the circuit. 

--  If the other device is designed to use less power than the bulb, then the
other device gets more power than the bulb gets.

--  If the other device is designed to use more power than the bulb, then the
other device gets less power than the bulb gets.

--  If the other device is removed from the circuit, then the bulb doesn't light at all.

This description of the often-screwy behavior of a series circuit may partly explain
why the electric service in your home is not a series circuit.

Answer 2

Nothing special happens. It just lights up normally. A series circuit is a normal circuit, the different one is a parallel circuit.