☰ Year plan · Science

Making circuits (2)

Week 29 · Unit 6 · 6.3 · 3 lessons
1

Why won’t it light?

Workbook 2: Topic 6.3, pp. 75–80
GoalFind out why a lamp does not light, such as a gap in the circuit, a loose wire or a missing cell.
New words
broken circuit · a circuit with a gap, so electricity cannot flow all the way roundgap · a space where the loop is not joinedloose · not held tightly in place
Explanation

Sometimes a lamp does not light. This is often because the circuit is broken. There may be a gap in the loop. A wire may have come loose from the cell or the lamp holder. A part may be missing, such as a cell. The lamp may not be screwed in tightly. Electricity cannot jump across a gap, so it stops. To fix the circuit, look along the loop and find the gap. Join it, tighten it or add the missing part, and the lamp lights.

What is wrong?How to fix it
a gap in the loopjoin the wires
a loose wirepush it on tightly
no cellput a cell in its holder
a loose lampscrew it in
Worked examples
gap−+
Zhu’s wire has slipped off the lamp holder. There is a gap, so the electricity stops and the lamp stays dark.
−+
Zhu pushes the wire back onto the lamp holder. The loop is complete again, and the lamp lights.
Leo forgot to put the cell in its holder. A circuit with no cell has nothing to push the electricity, so the lamp does not light.
Class activity

Circuit detective (with an adult or at school, small cells only): build a circuit that works. Then make one fault at a time, such as taking away a wire, loosening the lamp, or leaving out the cell. What happens each time? Mend it each time and check the lamp lights again.

Practice
1
A lamp does not light. Give two possible reasons.
2
A wire has fallen off the cell. Will the lamp light? Say why.
3
Look at the circuit. How can you make the lamp light?
gap−+−+
4
Cora makes a circuit with two wires and a lamp but no cell. Will it light? Say why.
Cora’s circuitHas it got one?
wiresyes
a lampyes
a cellno