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Primary Science · Year 6Chapter 10 · Components, switches and circuit symbols
Year 6 · Chapter 10

Components, switches and circuit symbols

By the end of this chapter you will be able to

  • Use the words open and closed for a switch, and say what each one does to a circuit
  • Explain why a bulb in a loop with two bulbs in a row is dimmer than a bulb on its own
  • Explain the difference in brightness and loudness using voltage and the loop
  • Name and draw the circuit symbols for a cell, a battery, a bulb, a switch, a wire and a motor
  • Read a circuit diagram, and say whether the bulb will light

You should already know

  • Complete circuits, cells and voltage (Chapter 9 of this book)
  • Electricity at a simple level, including bulbs, buzzers and switches (Year 4 Science)

Where this leads

  • Electrical components in more detail, including resistance, in later science

National Curriculum for England, Key Stage 2 science, Year 6. Content: EL2 compare and give reasons for variations in how components function, including the brightness of bulbs, the loudness of buzzers and the on/off position of switches, EL3 use recognised symbols when representing a simple circuit in a diagram.

Exercise P  Do you remember?

1
FWhat is the name of a circuit that is joined all the way round with no gaps? Write the two words.
2
FWhich part of a circuit gives the energy? Write the word.
3
FHow many volts does one standard cell give? Write the number.
4
FWhat is the word for the brightness rating a bulb gets, when it is brighter with more cells? Write the word: brighter or dimmer.
5
FWhat do we call a material that does not let electricity flow through it? Write the word.
10.1

Components and what they do

Year 6
EL2: compare and give reasons for variations in how components function, including the brightness of bulbs and the loudness of buzzers
Video lesson: Components and what they doComing soon
Story. Aisha builds a circuit with a cell, a bulb and a buzzer. “The bulb is bright, but the buzzer is quiet,” she says. Mr Patel says, “Each component works in its own way. The cells give the voltage, and the components use it in different ways.”

A component is a part of a circuit. The most common components are:

A component works differently depending on the voltage and on the rest of the loop. A higher voltage makes a bulb brighter and a buzzer louder.

The table gives the parts of a simple circuit.

ComponentWhat it does
cellprovides the voltage and the energy; it has a positive and a negative end
bulblights up when current flows through it
buzzermakes a sound when current flows through it
switchopens or closes the loop, turning the circuit off or on

Key ideas

  • A component is a part of a circuit, such as a cell, bulb, buzzer or switch.
  • A bulb lights up when current flows through it.
  • A buzzer makes a sound when current flows through it.
  • A higher voltage makes a bulb brighter and a buzzer louder.
Worked example 10.1.1
Which component gives the voltage to the circuit? Write the word.

Method. Read the description.

  1. Read the description. The cell gives the voltage and the energy to the circuit.
    gives the voltage
  2. Write the word. So the component is the cell.
    cell
  3. Write the answer.
    cell

Check. The bulb and buzzer use the energy from the cell. ✓

Worked example 10.1.2
Which component lights up when current flows through it? Write the word.

Method. Read the description.

  1. Read the description. A bulb lights up when current flows through it.
    lights up
  2. Write the word. So the component is the bulb.
    bulb
  3. Write the answer.
    bulb

Check. A buzzer makes a sound instead. ✓

Worked example 10.1.3
Two buzzers, one with 2 cells and one with 3 cells, are in complete loops. Which is louder? Write the number of cells.

Method. Use the rule about voltage.

  1. Think about the voltage. Three cells give a higher voltage than two cells.
    4.5 volts is more than 3.0 volts
  2. Decide. So the buzzer with 3 cells is louder.
    3
  3. Write the answer.
    3 cells

Check. The rating for 3 cells is 5 out of 5 in Chapter 9. ✓

Watch out

Watch out: a component depends on the rest of the circuit. A bulb in a different circuit may be brighter or dimmer, because the voltage and loop are different.

Exam tip

Exam tip. Name the component, then say what it does when current flows through it.

Try it (with your teacher, or a grown-up at home). With a teacher, build a loop with one cell, one bulb and one buzzer, joined in a row. Watch which component changes. Then add a second cell. Which component changes most? Write your answer in a sentence.

Exercise 10A  Components and what they do

1
FWhich component makes a sound when current flows through it? Write the word.
2
FWhich component lights up when current flows through it? Write the word.
3
FWhich component turns the circuit on or off? Write the word.
4
FWhich component gives the voltage? Write the word.
5
FDoes a higher voltage make a bulb brighter? Write yes or no.
6
FDoes a higher voltage make a buzzer louder? Write yes or no.
7
FA bulb is rated 2 with one cell, and 4 with two cells. Which has the higher voltage: one cell or two cells? Write the number of cells.
8
PSWhich component is used to start or stop the current, without removing a wire? Write the word.
9
PSAli says a bulb and a buzzer both need a complete loop to work. Is Ali right? Write yes or no.
10
PSPriya says a buzzer makes its sound because it gives out light. Is Priya right? Write yes or no.
11
RExplain why a bulb with three cells is brighter than a bulb with one cell. Write one sentence.
12
RExplain why the same bulb can be dimmer in one circuit than in another. Write one sentence.
13
RChallenge: explain why a component can be the same kind in two circuits, and still behave differently. Write one sentence.
10.2

Switches: open and closed

Year 6
EL2: compare and give reasons for the on/off position of switches
Video lesson: Switches: open and closedComing soon
Story. Tom tests a switch in his circuit. When the switch is up, the bulb is off. When he pushes it down, the bulb lights. “The switch makes a gap, and closes it,” says Tom. Priya says, “A gap stops the current, so the bulb has no current. Closing the gap makes a complete loop again.”

A switch is a component that can open or close a circuit.

Mcellbatterybulbmotorswitch openswitch closedwiresymbols are drawn the same way in every circuit diagram
Circuit symbols: a cell, a battery, a bulb, a motor, an open switch, a closed switch and a wire.

Six tests were made with one switch in a loop with a bulb. The table shows each test.

TestSwitchBulb lit?
Test 1openno
Test 2closedyes
Test 3closedyes
Test 4openno
Test 5closedyes
Test 6openno

Key ideas

  • A switch that is open makes a gap in the loop, so no current flows.
  • A switch that is closed makes the loop complete, so current flows.
  • The bulb is lit only when the switch is closed and the loop is complete.
  • A switch is a safe way to turn a circuit on or off.
Worked example 10.2.1
Look at the table in section 10.2. In how many tests was the switch closed? Write the number.

Method. Count the rows that say closed.

  1. Read the table. The rows that say closed are tests 2, 3 and 5.
    closed
  2. Count. That is three tests.
    3
  3. Write the answer.
    3

Check. Three tests were closed and three were open. ✓

Worked example 10.2.2
In test 4, the switch was open. Was the bulb lit? Write yes or no.

Method. Read test 4.

  1. Read the row. Test 4 has the switch open.
    open
  2. Decide. With the switch open there is a gap, so the bulb is not lit: the answer is no.
    no
  3. Write the answer.
    no

Check. The table says no for test 4. ✓

Worked example 10.2.3
How many tests did the bulb light? Write the number.

Method. Count the rows that say yes.

  1. Read the last column. The bulb lit in tests 2, 3 and 5.
    yes
  2. Count. So the bulb lit in 3 tests.
    3
  3. Write the answer.
    3

Check. The bulb lit only when the switch was closed. ✓

Watch out

Watch out: a closed switch does not mean the circuit is broken. A closed switch completes the loop; an open switch breaks it.

Exam tip

Exam tip. Say that an open switch makes a gap, so no current flows, and a closed switch completes the loop.

Try it (with your teacher, or a grown-up at home). With a teacher, build a loop with one cell, one bulb and a switch. Open and close the switch, and watch the bulb. Write down the position of the switch and whether the bulb is on, each time you test it.

Exercise 10B  Switches: open and closed

1
FWhat do we call a switch that has a gap in the loop? Write the word.
2
FWhat do we call a switch that completes the loop? Write the word.
3
FWhen a switch is open, does current flow round the loop? Write yes or no.
4
FWhen the switch is closed, is the bulb on or off? Write the word.
5
FLook at the table in section 10.2. How many tests had the switch open? Write the number.
6
FLook at the table in section 10.2. In test 6, was the bulb lit? Write yes or no.
7
FLook at the table in section 10.2. How many tests had the bulb lit? Write the number.
8
FIs a switch a safe way to turn off a circuit? Write yes or no.
9
PSPriya says the bulb is on when the switch is open. Is Priya right? Write yes or no.
10
PSA loop has a bulb, a cell and a switch. The switch is closed. Does the bulb light? Write yes or no.
11
PSA class tested a switch six times. How many tests were needed to show that the bulb lit only when the switch was closed? Write the number.
12
RExplain why a bulb goes off when a switch is opened, even though the cell is still connected. Write one sentence.
13
RChallenge: explain why a switch placed anywhere in the loop turns the whole circuit off. Write one sentence.
10.3

More bulbs in a loop

Year 6
EL2: compare and give reasons for variations in how components function, including the brightness of bulbs
Video lesson: More bulbs in a loopComing soon
Story. Mo adds a second bulb to his loop, joined in a row with the first. “Both bulbs look dimmer,” he says. “Why?” Mrs Chen says, “The same voltage now has to share between two bulbs. Each bulb gets less of it, so each one is dimmer.”

Bulbs can be joined one after another in a row, in the same loop. This is called joining them in series.

When two bulbs are in a row with one cell, the voltage is shared between them. Each bulb gets less current, so each one is dimmer than a single bulb with the same cell.

one cell, one bulb
A loop with one cell and one bulb.
one cell, two bulbs in a row
A loop with one cell and two bulbs in a row.

The table compares the brightness of the bulbs, rated out of 5, with two cells.

CircuitBrightness rating (out of 5)
2 cells, one bulb4
2 cells, two bulbs in a row (each bulb)2
012345brightness rating (out of 5)4one bulb2each of two bulbs
Bar chart: one bulb is rated 4 out of 5, and each bulb in a row of two is rated 2 out of 5.

Key ideas

  • Bulbs in a row in one loop share the voltage between them.
  • Each bulb in a row gets less current, so each one is dimmer.
  • One bulb on its own in the same loop is brighter.
  • Adding a bulb to a loop changes how bright all the bulbs in the loop are.
Worked example 10.3.1
Look at the table in section 10.3. How bright is one bulb on its own, with two cells? Write the rating out of 5.

Method. Read the table.

  1. Read the row. One bulb with two cells is rated 4 out of 5.
    4
  2. Write the rating. So the rating is 4 out of 5.
    4 out of 5
  3. Write the answer.
    4 out of 5

Check. The single bulb is brighter. ✓

Worked example 10.3.2
How much dimmer is each bulb in a row of two, compared with one bulb? Write the number of rating points.

Method. Subtract the two-bulb rating from the one-bulb rating.

  1. Read the ratings. One bulb is rated 4, and each of two bulbs is rated 2.
    4 and 2
  2. Subtract. The difference is 4 minus 2.
    4 - 2 = 2
  3. Write the answer.
    2 points

Check. 2 + 2 = 4. ✓

Worked example 10.3.3
Why is each bulb in a row dimmer than a single bulb? Write the reason in one sentence.

Method. Think about the voltage.

  1. Think about the voltage. The voltage is shared between the two bulbs.
    shared
  2. Think about the current. So each bulb gets less current, which makes it dimmer.
    less current
  3. Write the answer.
    the voltage is shared, so each bulb gets less current

Check. Sharing the voltage makes each bulb dimmer. ✓

Watch out

Watch out: two bulbs in a row do not each get the full voltage. The voltage is shared, so each bulb is dimmer than a single bulb.

Exam tip

Exam tip. When you explain a bulb being dimmer, say that the voltage is shared, so less current flows through each bulb.

Try it (with your teacher, or a grown-up at home). With a teacher, make a loop with one cell and one bulb. Note the brightness. Then add a second bulb in a row, and compare the brightness of both bulbs. Discuss why the bulbs are dimmer. Use ratings out of 5, and keep the cell the same.

Exercise 10C  More bulbs in a loop

1
FWhat is the brightness rating of one bulb with two cells? Write the number out of 5.
2
FWhat is the brightness rating of each bulb when two bulbs are in a row? Write the number out of 5.
3
FHow many more rating points is one bulb than each of two bulbs in a row? Write the number.
4
FAre the bulbs in a row dimmer than one bulb on its own? Write yes or no.
5
FWhich circuit has the brighter bulb: one bulb with two cells, or two bulbs in a row with two cells? Write one bulb or two bulbs in a row.
6
FIs the voltage shared between the bulbs in a row? Write yes or no.
7
FWhat do we call bulbs joined one after another in the same loop? Write the words.
8
PSA loop has one cell and one bulb rated 4. A second bulb is added in a row, and both are rated 2. How many points dimmer is each bulb? Write the number.
9
PSRuby says that adding a second bulb in a row makes the first bulb brighter. Is Ruby right? Write yes or no.
10
PSAli adds a bulb to a loop and says the bulbs are now the same brightness as one bulb. Is Ali right? Write yes or no.
11
RExplain why a bulb in a row of two is dimmer than a bulb on its own, in terms of the current. Write one sentence.
12
RExplain why the bulbs in a row are not as bright as a single bulb, even with the same cell. Write one sentence.
13
RChallenge: explain how you could make the two bulbs as bright as one bulb, by changing the cells. Write one sentence.
10.4

Circuit symbols

Year 6
EL3: use recognised symbols when representing a simple circuit in a diagram
Video lesson: Circuit symbolsComing soon
Story. Ruby draws a circuit for her science book. “I drew a little picture of each part,” she says. Mr Patel says, “Good, but scientists use symbols, so that everyone can read the same diagram. Let’s learn the symbols.”

A circuit diagram uses symbols to show each component, and straight lines for the wires. The same symbols are used in every country and every book, so a diagram can be read by anyone.

The table names each component and describes its symbol. The picture shows the symbols.

Mcellbatterybulbmotorswitch openswitch closedwiresymbols are drawn the same way in every circuit diagram
Circuit symbols: a cell, a battery, a bulb, a motor, an open switch, a closed switch and a wire.
ComponentIts symbol
cella long thin line and a short thick line
batterytwo or more cells drawn together
bulba circle with a cross inside it
switch (open)a line with a gap in it
switch (closed)a line with no gap, joined all the way across
wirea plain line
motor (non-statutory)a circle with the letter M inside it

Key ideas

  • A cell is drawn as a long thin line and a short thick line.
  • A bulb is a circle with a cross inside it.
  • A switch is a line with a gap, which is open; closed means the gap is joined.
  • Wires are plain straight lines, joined at the corners.
Worked example 10.4.1
In the symbol table, what is the symbol for a bulb? Write the words.

Method. Read the table.

  1. Read the table. A bulb is a circle with a cross inside it.
    circle with a cross
  2. Write the words. So the symbol is a circle with a cross inside it.
    circle with a cross
  3. Write the answer.
    a circle with a cross inside it

Check. The picture shows the same symbol. ✓

Worked example 10.4.2
In the symbol table, what is the symbol for an open switch? Write the words.

Method. Read the table.

  1. Read the table. An open switch is shown as a line with a gap in it.
    line with a gap
  2. Write the words. So the symbol is a line with a gap in it.
    line with a gap
  3. Write the answer.
    a line with a gap in it

Check. A closed switch has no gap. ✓

Worked example 10.4.3
How many long thin lines does a cell symbol have? Write the number.

Method. Look at the cell symbol.

  1. Look at the symbol. A cell is drawn as a long thin line and a short thick line.
    one long line
  2. Write the number. So a cell has one long thin line.
    1
  3. Write the answer.
    1

Check. The short thick line is the other part of the symbol. ✓

Watch out

Watch out: the long line is the positive end of a cell, and the short thick line is the negative end. Use the symbols exactly as they are drawn.

Exam tip

Exam tip. Draw the symbols neatly, use straight lines for wires, and draw a complete loop.

Try it (with your teacher, or a grown-up at home). Look at a simple circuit in a book or on a safe website, with a grown-up. Find the symbol for each part, and say its name aloud. Then draw the same circuit using symbols on paper.

Exercise 10D  Circuit symbols

1
FIn the symbol table, which symbol is a circle with a cross inside it? Write the name of the component.
2
FWhat is the symbol for a cell? Write the words.
3
FWhat is the symbol for a wire? Write the words.
4
FWhich component is a circle with the letter M inside it? Write the word.
5
FHow many cells are shown in the symbol for a battery? Write the number, using the picture.
6
FWhich symbol shows a switch that is closed? Write the words.
7
FIs a bulb symbol a circle? Write yes or no.
8
PSDraw a loop with a cell, a bulb and a closed switch using symbols. How many symbols did you draw in total? Write the number.
9
PSWhich symbol has a long thin line and a short thick line together? Write the name of the component.
10
PSPriya draws a bulb as a square. Is this the recognised symbol? Write yes or no.
11
RExplain why scientists use the same symbols in circuit diagrams. Write one sentence.
12
RChallenge: explain why a circuit diagram uses straight lines for wires, and not curves. Write one sentence.
10.5

Reading and drawing a circuit diagram

Year 6
EL3: use recognised symbols when representing a simple circuit in a diagram; read a circuit and say whether it works
Video lesson: Reading and drawing a circuit diagramComing soon
Story. Sam is given a circuit diagram and a box of parts. “Build the diagram, and tell me if the bulb will light,” says Mrs Chen. Sam reads each symbol, joins the parts in a complete loop, and then checks the switch. “It will light if the switch is closed,” he says. “That is what the diagram tells me.”

To read a circuit diagram, follow the lines round the loop. Check three things:

  1. Is every component joined in one complete loop?
  2. Is there a cell to give the voltage?
  3. Is the switch closed, so that there is no gap?

If all three are true, current flows, and the bulb lights.

a complete loop, with the switch closed
A complete loop with a cell, a closed switch and a bulb.
a loop with the switch open
A loop with a cell, an open switch and a bulb.

Key ideas

  • Follow the lines round the loop to check the circuit.
  • A complete loop with a cell and a closed switch lights the bulb.
  • An open switch makes a gap, so the bulb does not light.
  • Draw each part with its symbol, and join them with straight lines.
Worked example 10.5.1
In the first diagram in section 10.5, is the switch open or closed? Write the word.

Method. Look at the switch symbol.

  1. Read the symbol. The switch symbol is a line with no gap, joined all the way across.
    no gap
  2. Write the word. So the switch is closed.
    closed
  3. Write the answer.
    closed

Check. A closed switch completes the loop. ✓

Worked example 10.5.2
In the second diagram in section 10.5, will the bulb light? Write yes or no.

Method. Check the switch.

  1. Check the switch. The switch is open, so there is a gap in the loop.
    gap
  2. Decide. With a gap, no current flows, so the answer is no.
    no
  3. Write the answer.
    no

Check. Open means the bulb is off. ✓

Worked example 10.5.3
How many symbols are in the first diagram, not counting the wires? Write the number.

Method. Count the parts in the loop.

  1. Count. The loop has a cell, a closed switch and a bulb.
    three parts
  2. Write the number. So there are 3 symbols.
    3
  3. Write the answer.
    3

Check. The wires are not counted as components. ✓

Watch out

Watch out: a circuit diagram shows the path of the current, not the position of the parts on the page. Follow the lines, not the shapes.

Exam tip

Exam tip. When you read a circuit, check the loop is complete, the cell is there, and the switch is closed before you say a bulb lights.

Try it (with your teacher, or a grown-up at home). Draw a circuit with a cell, a closed switch and a bulb, using the symbols in this chapter. Then draw the same circuit with the switch open. Ask a partner to say whether the bulb lights in each diagram.

Exercise 10E  Reading and drawing a circuit diagram

1
FIs the switch in the first diagram in section 10.5 open or closed? Write the word.
2
FIn the second diagram in section 10.5, is the switch open or closed? Write the word.
3
FWill the bulb in the first diagram in section 10.5 light? Write yes or no.
4
FWill the bulb in the second diagram in section 10.5 light? Write yes or no.
5
FHow many symbols are in the second diagram, not counting the wires? Write the number.
6
FWhich part of the loop gives the voltage? Write the word.
7
FIs a circuit with a gap in its loop complete? Write yes or no.
8
PSA diagram has a cell, a closed switch and a bulb in a complete loop. How many volts does the cell give? Write the number, if the cell is a standard cell.
9
PSA diagram has two cells in a row, a closed switch and a bulb in a complete loop. What is the total voltage? Write the number of volts.
10
PSRuby says a diagram with an open switch will still light the bulb, because the cell is there. Is Ruby right? Write yes or no.
11
RExplain why the bulb does not light when the switch is open, even though all the other parts are connected. Write one sentence.
12
RChallenge: explain why a circuit diagram would be hard to read without symbols. Write one sentence.

Chapter summary

SkillMethod
ComponentsA cell gives the voltage. A bulb lights and a buzzer sounds when current flows through them.
SwitchesAn open switch is a gap, so no current flows. A closed switch completes the loop.
Bulbs in a rowBulbs in a row in one loop share the voltage, so each is dimmer than one bulb on its own.
SymbolsCell: long thin and short thick lines. Bulb: circle with a cross. Switch: a line with or without a gap. Wire: plain line.
DiagramsFollow the loop. Check it is complete, has a cell, and the switch is closed before saying a bulb lights.

Can you…?

  • I can say what an open and a closed switch do to a circuit
  • I can explain why bulbs in a row are dimmer than one bulb on its own
  • I can name the symbols for a cell, a battery, a bulb, a switch and a wire
  • I can read a circuit diagram and say whether the bulb will light
  • I can draw a simple circuit diagram using the recognised symbols

Key terms

component
a part of a circuit, such as a cell, bulb, buzzer or switch
switch
a component that opens or closes a circuit
open
a switch or loop that has a gap, so no current flows
closed
a switch or loop with no gap, so current can flow
in series
joined one after another in the same loop
circuit diagram
a drawing of a circuit that uses symbols for the parts and straight lines for the wires
symbol
a standard drawing that stands for a component in a circuit diagram
battery
two or more cells joined together

Exercise 10Z  Check-up

1
What is the symbol for a bulb? Write the words.
2
What is the symbol for an open switch? Write the words.
3
In the switch test table, how many tests had the bulb lit? Write the number.
4
Is a switch that is open a gap in the loop? Write yes or no.
5
In the table of bulbs in section 10.3, what is the rating of one bulb with two cells? Write the number out of 5.
6
What is the rating of each bulb in a row of two, from the table in section 10.3? Write the number out of 5.
7
Why is each bulb in a row of two dimmer than one bulb on its own? Write the words.
8
What is the total voltage of two cells joined end to end? Write the number of volts.
9
Ali draws a circuit with a gap in the loop and says the bulb will light. Is Ali right? Write yes or no.
10
Explain why a circuit with an open switch will not light a bulb, even with a cell. Write one sentence.

Total 15 marks. Allow about 15 minutes.

Exercise 10X  Practice test questions

1
FA switch is open in a loop with a cell and a bulb. Does the bulb light? Write yes or no.[1 mark]
2
FWrite the symbol for a bulb, using words. Write the words.[1 mark]
3
PSA table shows the bulb brightness rating: one bulb with two cells is 4 out of 5, and each of two bulbs in a row with two cells is 2 out of 5. Write the number of rating points that each bulb in the row is dimmer than the single bulb.[2 marks]
4
RExplain why two bulbs in a row are dimmer than one bulb with the same cells. Write one sentence.[2 marks]
5
FWrite the symbol for a cell, using words. Write the words.[1 mark]
6
FA diagram shows a cell, a closed switch and a bulb in a complete loop. Will the bulb light? Write yes or no.[1 mark]
7
FA class checked a switch six times. The bulb lit in three tests and not in the other three. Write the number of tests in which the switch was open.[1 mark]
8
RExplain why a bulb is off when the switch is open, even though the cell is still connected. Write one sentence.[2 marks]
9
PSRuby draws a circuit with a cell, a bulb and a switch, but the bulb is drawn as a square. Write one reason why this diagram does not follow the symbols.[2 marks]
10
PSA diagram has two cells in a row, a closed switch and one bulb. Write the total voltage of the cells, in volts.[2 marks]
← Chapter 9: Cells, brightness and volume

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