Sometimes an electric bulb does not glow even if it is connected to the cell. What could be the reason

Probable Reason - Break in filament of electric bulb

Explanation:

An electric bulb might not glow even if it is connected to the cell, possibly  because of break in the filament of electric bulb. As, break in bulb's filament implies break in flow of electric current - between electric cells' terminal.

An evident example of this is , a fuse bulb doesn't light up as the current doesn't pass through filament.

the independent variable, the one that is intentionally manipulated, is whether or not the car hits the barrier.

the dependent variable, the one that you measure the response in, is the distance that the washers travel.

the motion of a pendulum is a classic example of mechanical energy conservation. a pendulum consists of a mass (known as a bob ) attached by a string to a pivot point. as the pendulum moves it sweeps out a circular arc, moving back and forth in a periodic fashion.