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

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 explainwhy the electric service in your home is not a series circuit.

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