Quick parallels

This activity allows students to investigate up to three bulbs without them having to rebuild their circuit. You can use it to test their understanding of current in parallel circuits.

Equipment

Each group of students will need:

• Low voltage power supply (e.g. 1.5 V electrical cell)
• Three identical bulbs
• Two ammeters
• Eight 4 mm leads
• Glass of drinking water and straws (optional)

Preparation

Before the start of the lesson, set up one circuit as an exemplar so students can refer to it if required.

Drinking water through straws is a useful analogy for parallel circuits, but students should not eat or drink in labs. Only provide straws if you carry out the activity in a classroom.

Procedure

Ask the students to:

1. Set up the circuit below. To start only one bulb should be lit.

2. Record the readings on both ammeters (A1 and A2).
3. Predict what will happen when they connect lead Y.
4. Connect lead Y and record observations.
5. Repeat for lead Z.

Discussion prompts

• Why must the ammeter readings always be the same?
• Why do they go up when you connect leads Y and Z?

Teaching notes

Most students should be able explain why the readings on the ammeters are the same. The meters show the rate at which charges flow in and out of the cell. The two values must be the same because charge isn’t used up in a circuit.

For students that struggle to explain why readings increase when they connect leads Y and Z, a useful analogy is drinking water through straws. Adding more bulbs in parallel is like increasing the number of straws: the overall rate of flow increases because there are more parallel paths along which the flow can happen.

Learning outcome

Students predict and explain how the current will change when two or more bulbs are connected in parallel.

This experiment was safety-checked in March 2020.