A series circuit has all the items arranged in a row, one after the other, so electrons follow one single path. When you put batteries into a flashlight from end to end, they are creating a series circuit.

You can connect together two or more power supplies to increase the amount of power sent to an electrical device. You can also connect two or more electrical devices to share a power supply–unfortunately, that drains batteries more quickly.

Electricity can only flow in one direction. It is interrupted when any part of a series circuit is missing. If you take away a battery or a light bulb, the flow of electricity stops–the electrons go back to orbiting a nucleus, or drift around without direction.

The bulbs don't light up, even though the switch is still closed. It wouldn't matter whether the batteries were placed before or after the light bulbs in the circuit.