You will need three bulbs in their holders, some connecting wire and a battery in its holder.

First, make sure you know what the bulbs say on their sides. Some will say 3V, some will say 4.5V and so on. Now make sure your battery matches whichever number is on the bulb.

Connect the bulb across the battery using the connecting wires. It will light brightly. Now put another bulb in the circuit. Finally, put a third bulb in the circuit. Do not change the battery during this experiment.

Do the extra bulbs glow less brightly than the first, or do all bulbs glow by the same amount?