☰ Year plan · Science

Making circuits (1)

Week 28 · Unit 6 · 6.3 · 3 lessons
2

A complete circuit

Workbook 2: Topic 6.3, pp. 75–80
GoalExplain that a lamp lights only when the cell, the wires and the lamp make one closed loop.
New words
circuit · a path that electricity can flow round, like a loopcomplete circuit · a circuit with no gaps in itflow · to move along steadily
Explanation

Electricity can only move along a path. It leaves one end of the cell. It flows along a wire, through the lamp, and back along another wire to the other end of the cell. The path makes a loop. We call it a circuit. If the loop is complete, with no gaps, the electricity keeps flowing and the lamp lights. Both ends of the cell must be joined to the lamp with wires. We use only small cells to make our circuits.

The circuitDoes the lamp light?
cell, wires and lamp joined in a loopyes
one wire not joined: a gapno
Worked examples
−+
Kenji joins a cell, two wires and a lamp in a loop. The electricity can flow all the way round, so the lamp lights.
Sara checks that each wire touches the metal parts, so there are no gaps. A complete circuit is like a road that goes all the way round with no breaks.
gap−+a gap: no light
If one wire is not joined, there is a gap. The electricity cannot get round, so the lamp stays dark. A cell needs the whole loop.
Class activity

Build a circuit (with an adult or at school, using small cells only): join a cell holder, a lamp holder and two wires so that they make a loop. Watch the lamp. Then take one wire off, and put it back. Say what happened each time. Never use mains electricity or a socket for this.

Practice
1
What do we call a loop that electricity can flow round?
2
What do you need to make a lamp light? Choose from: a cell, a spoon, two wires, a lamp, a ribbon.
3
What must the wires join to at both ends of the cell?
celllamp
4
A complete circuit is like a road that goes all the way round. Why?