Grade 4 · Unit 5: Electricity and magnetism

Circuits with more components

More cells, brighter bulbs. More bulbs, dimmer bulbs.

Two cells give more push than one, so the bulb shines brighter.

Adding cells

Adding a second cell gives the current a bigger push. The voltage goes up and the bulb shines brighter. Cells must face the same way, + to –.

Cells joined end to end add their voltages together: two 1.5 V cells give 3 V.

Adding bulbs

Adding a second bulb in the same loop makes both bulbs dimmer. The bulbs share the push from the cell. A circuit with everything in one loop is a series circuit.

Some circuits use branches, so that each bulb gets the full push. You will learn about these in later grades.

Too much push

If you use too many cells, the bulb gets very bright and then breaks. It “blows”. Always use the right number of cells for a bulb. The bulb is marked with its voltage.

A bulb or device is labelled with the voltage it needs. A 3 V torch bulb will blow if you connect it to a 9 V battery.

Comparing circuits

Change only one thing at a time to see what it does. Record the brightness of the bulbs each time.

A good scientist records exactly what was changed, for example “1 cell and 2 bulbs”, so others can repeat the test.

What I learnt