Year 4 Science · Switches, conductors and insulators · Lesson 10.1

Year 4 Science: A switch opens and closes a circuit

Part of the Year 4 Science switches, conductors and insulators chapter. Chapter overview · whole chapter on one page

10.1

A switch opens and closes a circuit

Year 4
E4: recognise that a switch opens and closes a circuit, and associate this with whether or not a lamp lights

Story. Mo has a torch with a switch on the side. He slides it along, and the light comes on. He slides it back, and the light goes out. “What is the switch doing inside?” he asks. Ms Chen says, “It opens and closes the loop of the circuit.”

A switch is a part of a circuit that can be closed or open. When the switch is closed, it completes the loop, so the electricity can flow and the lamp lights. When the switch is open, the loop is broken, so the electricity cannot flow and the lamp does not light.

A closed switch: the loop is complete, so the lamp lights.

An open switch: the loop is broken, so the lamp does not light.

Switch	The loop	The lamp
closed	complete	lights
open	broken	does not light

Key ideas

A closed switch completes the loop, so the lamp lights.
An open switch breaks the loop, so the lamp does not light.
A switch opens and closes the circuit.
Switching the lamp on and off means opening and closing the switch.

Worked example 10.1.1

Look at the table in section 10.1. Which switch position lights the lamp? Write the word: closed or open.

Method. Read the table.

Find the lights row. The row that says lights is the closed switch.
closed
Name the position. So the switch must be closed for the lamp to light.
closed
Write the answer.
closed

Check. A closed switch completes the loop. ✓

Worked example 10.1.2

When the switch is open, is the loop complete or broken? Write the word.

Method. Think about an open switch.

Think about the loop. An open switch breaks the loop.
breaks
Name the state. So the loop is broken.
broken
Write the answer.
broken

Check. The lamp does not light when the loop is broken. ✓

Worked example 10.1.3

Does a lamp light when the switch is open? Write yes or no.

Method. Read the table.

Find the open row. The open row says the lamp does not light.
does not light
Decide. So the answer is no.
no
Write the answer.
no

Check. An open switch breaks the loop. ✓

Watch out

Watch out: a switch is not a lamp. The switch controls whether the loop is complete. If the switch is closed but the bulb is broken, the lamp still does not light.

Try it at home or school (with a grown-up). With a grown-up, use a cell, a bulb in a holder, two wires and a simple switch to make a loop. Close the switch, and watch the bulb. Then open it. Do not touch the bulb while it is hot.

Exam tip

Grown-up tip. Ask: “Is the switch open or closed? Is the loop complete?” Let your child open and close the switch, and say what the lamp does each time.

Exercise 10A A switch opens and closes a circuit

FDoes a closed switch complete the loop? Write yes or no.

Done

FDoes an open switch break the loop? Write yes or no.

Done

FDoes a lamp light when the switch is open? Write yes or no.

Done

FFill in the gap: a switch opens and ___ a circuit. Write the word.

Done

FLook at the table in section 10.1. Which switch position lights the lamp? Write the word: closed or open.

Done

FLook at the table in section 10.1. Which switch position leaves the loop broken? Write the word: closed or open.

Done

FHow many positions does a simple on-off switch have? Write the number.

Done

FWhich word describes the loop when the switch is open: complete or broken? Write the word.

Done

PSRuby says a lamp lights when the switch is open. Is Ruby right? Write yes or no.

Done

PSAli closes the switch. Does the electricity flow round the loop? Write yes or no.

Done

PSWorking scientifically. Predict whether the lamp will light when the switch is closed. Write yes or no, and then test it with a grown-up.

Done

RExplain how a switch turns a lamp on and off. Write one sentence.

Done