2
Switches
Workbook 2: Topic 6.3, pp. 75–80
GoalSay that a switch opens and closes a circuit, so it turns a lamp off and on.
New words
switch · a part that opens or closes the circuitopen · with a gap in the circuit, so the lamp is offclosed · joined, so the circuit is complete and the lamp is on
Explanation
A switch is a part that can make a gap in a circuit. When the switch is open, there is a gap. The electricity cannot flow, so the lamp is off. When we close the switch, the gap is joined. The circuit is complete, and the lamp is on. A switch is a useful way to turn things on and off without taking a wire away. Our room lights, torches and toys all have switches.
| The switch is | Is there a gap? | The lamp is |
|---|---|---|
| open | yes | off |
| closed | no | on |
Worked examples
Here the switch is open. There is a gap in the loop, so the lamp is not lit.
Then the switch is closed. The loop is complete, so the lamp is lit.
A torch has a switch inside. You slide it to join the circuit and the lamp lights. Slide it back and the lamp goes off.
Class activity
Switch hunt (with an adult): find five things with a switch, such as a torch, a toy and a bedside lamp. You may switch on the torch and the toy. Let the adult switch anything that plugs into the wall. For each one, say what happens inside when the switch is closed, and what happens when it is open. Then draw a circuit with a switch.
Practice
1
What does a switch do?
It opens and closes a circuit, so it turns things on and off.
2
Name the three parts of this circuit.
A cell, a lamp and a switch (with wires).
3
The switch is open. Is the circuit complete? Is the lamp on or off?
No. The open switch makes a gap, so the lamp is off.
4
Look at this circuit. What can you do to make the motor stop, without taking a wire off?
Open the switch. That makes a gap, so the motor stops.