Free textbooks › Year 9 Science textbook
KS3 Science · Year 9Chapter 11 · Magnets and electromagnets
Year 9 · Chapter 11

Magnets and electromagnets

By the end of this chapter you will be able to

  • Describe the forces between poles, and name the magnetic materials
  • Draw and read magnetic field lines around a magnet and around a wire
  • Distinguish permanent and induced magnets
  • Describe how the current, the number of turns and the iron core change an electromagnet
  • Explain the motor effect in simple terms (extension)

You should already know

  • Magnets and magnetic materials in earlier school science
  • Circuits, current and series circuits (Chapter 10)

Where this leads

  • Waves and the electromagnetic spectrum in Chapter 13, where electromagnetic waves are described

National Curriculum for England, Key Stage 3 science, Year 9. Content: 9P4 magnetic poles, attraction and repulsion; permanent and induced magnets, 9P4 magnetic fields and field lines, drawn around magnets and around current-carrying wires, 9P4 electromagnets: a solenoid with an iron core; factors that change the strength (current, number of turns, core); uses, 9P4 the motor effect (basic; EXTENSION: top of the KS3 range, flagged).

Exercise P  Do you remember?

1
FWhat is the name of the particle that carries a negative charge in an atom? Write the word.
2
FWhat is 2 x 15? Write the number.
3
FWhat is the name of the component that switches a circuit on or off? Write the word.
4
FWhich metal is most commonly used to make a magnet that is attracted to a magnet? Write the word.
5
FWhat is 60 divided by 4? Write the number.
11.1

Magnets and magnetic forces

Year 9
9P4: magnetic poles, attraction and repulsion
Video lesson: Magnets and magnetic forcesComing soon
Story. Ruby has two bar magnets. When she brings two ends together, they push apart. When she turns one magnet round, they pull together. She asks her teacher why the same magnets can both push and pull.

Every magnet has two poles: a north pole and a south pole. Like poles repel: two north poles push apart, and so do two south poles. Unlike poles attract: a north pole and a south pole pull together.

Magnets attract iron, steel, nickel and cobalt. Materials such as copper, aluminium, wood and plastic are not attracted to a magnet.

PolesWhat happens
N and Nrepel
S and Srepel
N and Sattract
The forces between poles

Key ideas

  • Every magnet has a north pole and a south pole.
  • Like poles repel; unlike poles attract.
  • Iron, steel, nickel and cobalt are magnetic materials.
  • Copper, aluminium, wood and plastic are not attracted to a magnet.
Worked example 11.1.1
Two north poles are brought together. Do they attract or repel? Write the word.

Method. Recall the rule for like poles.

  1. Recall. Like poles repel.
    like poles repel
  2. Name it. Two north poles repel each other.
    repel
  3. Write the answer.
    repel

Check. Like poles push apart. ✓

Worked example 11.1.2
A north pole is brought near a south pole. Do they attract or repel? Write the word.

Method. Recall the rule for unlike poles.

  1. Recall. Unlike poles attract.
    unlike poles attract
  2. Name it. A north and a south pole attract.
    attract
  3. Write the answer.
    attract

Check. Unlike poles pull together. ✓

Worked example 11.1.3
Name a metal that a magnet attracts, and one that it does not. Accept any one of each.

Method. Recall the magnetic materials.

  1. Recall. Iron is attracted by a magnet.
    iron is attracted
  2. Name it. Copper is not attracted by a magnet.
    copper is not
  3. Write the answer.
    Accept iron, steel, nickel or cobalt; and copper or aluminium.

Check. Iron is attracted; copper is not. ✓

Watch out

Watch out: a magnet does not attract all metals. Aluminium and copper are not magnetic materials.

Exam tip

Exam tip. Say “like poles repel” and “unlike poles attract” exactly, since the words are often swapped.

Try it (with your teacher, or a grown-up at home). With your teacher, bring two bar magnets close together, both ways round, and watch whether they attract or repel. Then test a paper clip, a copper coin and a plastic ruler. Keep fingers clear of the magnets, which can snap together.

Exercise 11A  Magnets and magnetic forces

1
FWhat are the two ends of a magnet called? Write the words.
2
FDo two north poles attract or repel? Write the word.
3
FDo a north pole and a south pole attract or repel? Write the word.
4
FName the four magnetic materials in this list: iron, steel, nickel, cobalt. Write the number of them that are magnetic.
5
FIs copper attracted by a magnet? Write yes or no.
6
FIs aluminium attracted by a magnet? Write yes or no.
7
FWhich material is a magnet attracted to: wood or steel? Write the word.
8
PSTwo bar magnets are placed with their north poles facing each other. Do they push apart or pull together? Write the words.
9
PSA north pole is held near the south pole of another magnet. Do they push apart or pull together? Write the words.
10
PSA magnet is placed on a table. A pupil sees that a paper clip is attracted to one end but not to the other. Is this possible? Write yes or no.
11
PSWhich two materials are not attracted by a magnet: copper and steel, or copper and aluminium? Write the words.
12
RExplain why a magnet can pick up a steel nail but not a plastic pen. Write one sentence. Accept any sentence saying steel is a magnetic material, so it is attracted, but plastic is not.
13
RChallenge: explain why two magnets can attract at one end and repel at the other. Write one sentence. Accept any sentence saying an unlike pole pair attracts, but a like pole pair repels.
11.2

Magnetic fields and field lines

Year 9
9P4: magnetic fields, drawn with a compass and represented by field lines, around magnets and around current-carrying wires
Video lesson: Magnetic fields and field linesComing soon
Story. A pupil places a plotting compass near a bar magnet. The compass needle points in a different direction at each spot. She draws a line from each needle to show the pattern. The teacher says she has drawn field lines.

A magnetic field is the region where a magnetic force acts. A small plotting compass shows the direction of the field at any point. The field lines are drawn from the north pole to the south pole, outside the magnet. Field lines never cross, and the lines are closer together where the field is stronger.

A current in a straight wire also has a magnetic field. The field lines are circles around the wire, and the field is stronger when the current is larger.

NSfield lines run from the north pole to the south pole
A bar magnet with field lines running from its north pole to its south pole

Key ideas

  • Field lines point from north to south outside a magnet.
  • Field lines never cross.
  • Closer field lines mean a stronger field.
  • A current in a wire gives circular field lines around the wire.
Worked example 11.2.1
In which direction do the field lines point outside a bar magnet? Write the words.

Method. Recall the direction.

  1. Recall. Outside a magnet, field lines run from the north pole to the south pole.
    north pole to the south pole
  2. Name it. So they point from north to south.
    north to south
  3. Write the answer.
    from north to south

Check. The field is directed away from the north pole. ✓

Worked example 11.2.2
Where is the field strongest on a bar magnet: where the lines are close together or far apart? Write the words.

Method. Think about the spacing.

  1. Think. A strong field has field lines close together.
    close together
  2. Name it. So the field is strongest where the lines are close together.
    close together
  3. Write the answer.
    where the lines are close together

Check. Spacing shows strength. ✓

Worked example 11.2.3
What shape are the field lines around a straight wire carrying a current? Write the word.

Method. Recall the shape.

  1. Recall. A current in a straight wire gives a field round the wire.
    round the wire
  2. Name it. The field lines are circles around the wire.
    circles
  3. Write the answer.
    circles

Check. The field lines do not start or end on the wire. ✓

Watch out

Watch out: field lines are drawn from north to south outside a magnet, but they are not physical strings. They show the direction of the force.

Exam tip

Exam tip. Draw arrows on field lines to show direction, and label the poles of the magnet.

Try it (with your teacher, or a grown-up at home). With your teacher, place a bar magnet under a sheet of paper and sprinkle iron filings on top. Tap gently and look at the pattern. Draw the field lines you see, and mark where the lines are closest together. Keep the filings away from the eyes.

Exercise 11B  Magnetic fields and field lines

1
FWhat is a magnetic field? Write the words.
2
FWhat instrument shows the direction of a magnetic field at a point? Write the words.
3
FDo field lines cross each other? Write yes or no.
4
FOutside a magnet, do field lines go from north to south or south to north? Write the words.
5
FWhere is a magnetic field strongest: where the field lines are close, or far apart? Write the words.
6
FWhat is the shape of the magnetic field around a straight wire carrying a current? Write the word.
7
PSA pupil draws field lines that cross. Is this correct? Write yes or no.
8
PSIn the diagram of a bar magnet, the field lines are closest at the poles. Are the poles the strongest part of the field? Write yes or no.
9
PSWhich way does a plotting compass needle point, relative to the field line? Write the word: along or across.
10
PSA straight wire carries a larger current. Is its magnetic field stronger or weaker? Write the word.
11
RExplain why field lines are drawn from north to south, and not the other way. Write one sentence. Accept any sentence saying the convention is to show the direction a north pole would be pushed.
12
RChallenge: explain why the compass needles near a wire carrying a current all point in circles. Accept any sentence saying each needle lines up with the circular field lines round the wire.
11.3

Permanent and induced magnets

Year 9
9P4: permanent and induced magnets
Video lesson: Permanent and induced magnetsComing soon
Story. A pupil touches a steel paper clip to the end of a bar magnet, and it becomes a magnet for a short time: it picks up other clips. When the bar magnet is removed, the clips drop. The teacher says the clip is an induced magnet.

A permanent magnet keeps its magnetism all the time, for example a bar magnet made of steel. An induced magnet is a material that becomes a magnet only when it is placed in a magnetic field. Iron is a soft magnetic material: it is easily magnetised, but it loses its magnetism when the field is removed. Steel is hard: it is harder to magnetise, but it keeps its magnetism.

Key ideas

  • A permanent magnet keeps its magnetism.
  • An induced magnet is magnetised only while it is in a magnetic field.
  • Soft iron is easily magnetised and loses its magnetism quickly.
  • Steel is harder to magnetise and keeps its magnetism.
Worked example 11.3.1
A magnet keeps its magnetism all the time. Is it a permanent or an induced magnet? Write the word.

Method. Recall the difference.

  1. Recall. A permanent magnet keeps its magnetism at all times.
    at all times
  2. Name it. So it is a permanent magnet.
    permanent
  3. Write the answer.
    permanent

Check. An induced magnet is only magnetic in a field. ✓

Worked example 11.3.2
A soft iron bar is magnetised by a magnet, and loses its magnetism when the magnet is removed. What type of magnet is the iron? Write the words.

Method. Recall what happens to the iron.

  1. Recall. It is magnetised only while the field is present.
    only while
  2. Name it. So the iron is an induced magnet.
    induced magnet
  3. Write the answer.
    induced magnet

Check. Soft iron is a good example of an induced magnet. ✓

Worked example 11.3.3
Which is harder to magnetise: soft iron or steel? Write the word.

Method. Recall the properties.

  1. Recall. Steel is harder to magnetise than soft iron.
    harder to magnetise
  2. Name it. So steel is the harder one to magnetise.
    steel
  3. Write the answer.
    steel

Check. Steel keeps its magnetism when the field is removed. ✓

Watch out

Watch out: an induced magnet is attracted by the magnet that magnetised it, and always attracts, never repels, the magnet.

Exam tip

Exam tip. A permanent magnet is always magnetic; an induced magnet is only magnetic while it is in a field.

Try it (with your teacher, or a grown-up at home). With your teacher, touch a paper clip to one end of a bar magnet, and see how many other clips it picks up. Then remove the magnet and count again. Repeat with a steel nail. Say which is the induced magnet, and which keeps its magnetism.

Exercise 11C  Permanent and induced magnets

1
FWhat is the name of a magnet that keeps its magnetism all the time? Write the words.
2
FWhat is the name of a material that becomes a magnet only in a magnetic field? Write the words.
3
FIs soft iron easily magnetised, and does it lose its magnetism quickly? Write yes or no.
4
FWhich material keeps its magnetism when the magnetic field is removed: soft iron or steel? Write the word.
5
FDoes an induced magnet ever repel the magnet that magnetised it? Write yes or no.
6
PSA paper clip picks up 3 other clips while touching a magnet, and drops them when the magnet is removed. What type of magnet is the clip? Write the words.
7
PSA steel bar is magnetised, and still picks up clips a day later. What type of magnet is it? Write the words.
8
PSA pupil says a soft iron bar magnetised by a magnet will repel it. Is she right? Write yes or no.
9
PSWhich is more suitable for a magnet in a compass: soft iron, or steel? Write the word.
10
RExplain why soft iron is used in the core of an electromagnet, and not steel. Write one sentence. Accept any sentence saying soft iron loses its magnetism when the current is off, which lets the electromagnet be switched off.
11
RChallenge: explain why a magnetised steel bar can be used to magnetise other pieces of steel, but not as easily as iron. Accept any sentence saying steel is harder to magnetise, but it keeps its magnetism, so it is a good permanent magnet.
11.4

Electromagnets and their strength

Year 9
9P4: electromagnets: a solenoid with an iron core; factors that change the strength (current, number of turns, core); uses
Video lesson: Electromagnets and their strengthComing soon
Story. A scrapyard worker uses a large electromagnet on a crane to lift iron and steel scrap, and switches it off to drop the load. A class builds a small electromagnet with a coil and an iron core, and tests how many clips it picks up.

An electromagnet is a coil of wire with a current. A coil with many turns is a solenoid, and its field is like that of a bar magnet. The field is strongest inside the coil. Adding an iron core makes the field much stronger. Electromagnets can be switched on and off with the current.

The strength of an electromagnet increases when the current increases, when the number of turns increases, and when an iron core is added.

iron corecellmore turns, more current, or an iron core makes a stronger magnet
A solenoid: a coil of wire round an iron core, connected to a cell
TurnsClips picked up (1 A)
104
208
3012
Class results: clips picked up at 1 A, for different numbers of turns (iron core)
Current (A)Clips picked up (20 turns)
0.54
1.08
1.512
Class results: clips picked up with 20 turns (iron core), for different currents
UseWhy an electromagnet is suitable
scrapyard cranethe magnet can be switched off to drop the metal
electric bellthe coil pulls a hammer when the circuit is on; a spring returns it
relay switcha small current switches a larger current on and off
Uses of electromagnets and why they suit each job

Key ideas

  • An electromagnet is a coil with a current; it can be switched on and off.
  • Strength increases with more current, more turns, and an iron core.
  • A solenoid is a coil with many turns; its field is like a bar magnet.
  • Electromagnets are used in cranes, bells and relays.
Worked example 11.4.1
At 1 A, the coil has 20 turns and picks up 8 clips. How many clips would 30 turns pick up at 1 A? Write the number. (Use the class table: clips rise in proportion to turns.)

Method. Read the table, then compare.

  1. Read. At 1 A, 10 turns gave 4 clips, and 20 turns gave 8 clips.
    4 and 8
  2. Find. At 30 turns the table gives 12 clips.
    12
  3. Write the answer.
    12

Check. Clips rise in step with the turns. ✓

Worked example 11.4.2
With 20 turns, the coil picks up 4 clips at 0.5 A and 8 clips at 1 A. What happens to the strength when the current is doubled? Write the words.

Method. Compare the two currents.

  1. Compare. Doubling the current from 0.5 A to 1 A doubles the clips from 4 to 8.
    doubles
  2. Name it. So the strength doubles when the current doubles.
    doubles
  3. Write the answer.
    it doubles

Check. Current is one of the factors. ✓

Worked example 11.4.3
Name the factor that makes the electromagnet much stronger when it is added to the coil. Write the words.

Method. Recall the factors.

  1. Recall. An iron core makes the field much stronger.
    much stronger
  2. Name it. The factor is the iron core.
    iron core
  3. Write the answer.
    iron core

Check. The core is a soft magnetic material. ✓

Watch out

Watch out: adding a core does not make the coil stronger on its own; it works only when the coil has a current in it.

Exam tip

Exam tip. When asked how to make an electromagnet stronger, name all three factors: more current, more turns, and an iron core.

Try it (with your teacher, or a grown-up at home). With your teacher, wind 20 turns of insulated wire round a large iron nail, connect it to a low-voltage cell for a few seconds only, and test how many paper clips it picks up. Do not leave the current on, as the coil gets warm. Repeat with 10 turns, and say which factor changed.

Exercise 11D  Electromagnets and their strength

1
FWhat is an electromagnet? Write the words.
2
FWhat is the name of a coil with many turns, whose field is like a bar magnet? Write the word.
3
FName the core material that makes an electromagnet much stronger. Write the words.
4
FDoes increasing the current make an electromagnet stronger? Write yes or no.
5
FDoes adding more turns to the coil make the electromagnet stronger? Write yes or no.
6
FName an everyday use of an electromagnet. Accept any one: a scrapyard crane, an electric bell, or a relay.
7
PSAt 1 A with an iron core, 10 turns pick up 4 clips. How many clips would 20 turns pick up? Write the number.
8
PSWith 20 turns, the coil picks up 12 clips at 1.5 A. How many clips would 0.5 A give? Write the number.
9
PSAn electromagnet picks up 3 clips without a core and 8 with an iron core. How many more clips does the core add? Write the number.
10
PSA coil picks up 4 clips at 0.5 A and 8 clips at 1 A. What is the ratio of clips at 1 A to clips at 0.5 A? Write the number.
11
RExplain why an electromagnet is better than a permanent magnet for a scrapyard crane. Write one sentence. Accept any sentence saying it can be switched off to drop the metal.
12
RChallenge: explain why a coil with an iron core and many turns, at a high current, is the strongest type of electromagnet. Accept any sentence naming all three factors: an iron core, many turns and a high current.
11.5

The motor effect (extension)

Year 9
9P4: the motor effect (basic; EXTENSION: top of the KS3 range, flagged)
Video lesson: The motor effect (extension)Coming soon
Story. A pupil places a wire carrying a current between the poles of a magnet. When the current is switched on, the wire moves. Her teacher says this is the motor effect, and that the same principle is used in an electric motor. This section is an extension.

Extension (top of the KS3 range; flagged). A wire carrying a current in a magnetic field experiences a force. This is the motor effect. The force is largest when the wire is at right angles to the field. It increases when the current increases or the field is stronger. Reversing the current, or the direction of the field, reverses the direction of the force.

An electric motor uses the motor effect to turn a coil continuously, using a commutator to reverse the current each half turn. Principles only are needed here.

Key ideas

  • Extension: a current-carrying wire in a magnetic field feels a force (the motor effect).
  • The force increases with a larger current or a stronger field.
  • Reversing the current reverses the direction of the force.
  • An electric motor uses this force to turn a coil.
Worked example 11.5.1
A wire carries a current, and the force on it is 2 N. The current is doubled and the field is the same. Is the new force bigger or smaller? Write the word. (Extension.)

Method. Use the rule that force increases with current.

  1. Think. The force increases with the current in the wire.
    increases with current
  2. Decide. Doubling the current makes the force bigger.
    bigger
  3. Write the answer.
    bigger

Check. The force is larger when the current is larger. ✓

Worked example 11.5.2
The current in a wire is reversed. Does the direction of the force change? Write yes or no. (Extension.)

Method. Recall the rule.

  1. Recall. Reversing the current reverses the force.
    reverses the force
  2. Decide. So the direction changes; the answer is yes.
    yes
  3. Write the answer.
    yes

Check. The force reverses with the current. ✓

Worked example 11.5.3
In which position is the force on the wire largest: parallel to the field, or at right angles to it? Write the words. (Extension.)

Method. Recall the position.

  1. Recall. The force is largest when the wire is at right angles to the field.
    right angles
  2. Name it. So the force is largest at right angles.
    right angles
  3. Write the answer.
    at right angles

Check. Parallel to the field gives no force. ✓

Watch out

Watch out: the motor effect needs both a current and a magnetic field. A wire in a field with no current does not move.

Exam tip

Exam tip. Name the three things that change the motor effect: the current, the field strength, and the angle between the wire and the field.

Try it (with your teacher, or a grown-up at home). Teacher demonstration only, using a low-voltage supply and a simple demonstration motor kit. Pupils watch which way the coil turns when the current is reversed. Do not touch the coil while it is running.

Exercise 11E  The motor effect (extension)

1
FWhat is the name of the force on a current-carrying wire in a magnetic field? Write the words. (Extension.)
2
FDoes a wire with a current in a magnetic field always feel a force? Write yes or no. (Extension.)
3
FDoes reversing the current reverse the direction of the force? Write yes or no. (Extension.)
4
FIs the force largest when the wire is parallel to the field, or at right angles? Write the words. (Extension.)
5
FName the device that uses the motor effect to turn continuously. Write the word. (Extension.)
6
RIn a motor, what does the commutator do? Write one sentence. (Extension.) Accept any sentence saying it reverses the current each half turn, so the coil keeps turning.
7
PSA wire carries a current in a magnetic field, and feels a force of 4 N. If the current is halved, what is the new force, in newtons? (Extension.) Write the number.
8
RExplain why a wire placed parallel to a magnetic field does not feel a force. Write one sentence. (Extension.) Accept any sentence saying the current is then along the field, so no force is produced.
9
RChallenge: explain why a motor is more powerful when a stronger magnet is used, even with the same current. (Extension.) Accept any sentence saying a stronger field gives a bigger force on the coil for the same current.

Chapter summary

SkillMethod
PolesLike poles repel; unlike poles attract. Iron, steel, nickel and cobalt are magnetic.
Field linesNorth to south outside a magnet; they never cross; closer lines mean a stronger field; a wire gives circles.
Permanent and inducedPermanent keeps its magnetism; induced is magnetised only in a field; soft iron loses it, steel keeps it.
ElectromagnetsA coil with a current; stronger with more current, more turns and an iron core; can be switched off.
UsesScrapyard cranes, bells and relays (switching).
Motor effect (extension)A current in a field feels a force; larger with more current or a stronger field; reversed by reversing the current.

Can you…?

  • I can describe the forces between poles, and name the magnetic materials
  • I can draw and read magnetic field lines around a magnet and a wire
  • I can distinguish permanent and induced magnets
  • I can describe how the current, the turns and the core change an electromagnet
  • I can explain the motor effect in simple terms (extension)

Key terms

pole
one of the two ends of a magnet, north or south
magnetic field
the region where a magnetic force acts
field line
a line showing the direction of a magnetic field, from north to south outside a magnet
plotting compass
a small magnet that shows the direction of a magnetic field
permanent magnet
a magnet that keeps its magnetism all the time
induced magnet
a material that becomes a magnet only in a magnetic field
electromagnet
a coil of wire that is magnetic only when a current flows
solenoid
a coil of wire with many turns
motor effect
the force on a current-carrying wire in a magnetic field (extension)

Exercise 11Z  Check-up

1
Do like poles attract or repel? Write the word.
2
Name a material that is not attracted by a magnet. Accept any one: copper, aluminium, wood or plastic.
3
Outside a bar magnet, which way do the field lines point? Write the words.
4
Is a magnet that keeps its magnetism all the time a permanent or an induced magnet? Write the word.
5
Which material is easily magnetised and loses its magnetism quickly? Write the word.
6
Name the core material that makes an electromagnet much stronger. Write the words.
7
At 1 A with an iron core, 10 turns pick up 4 clips. How many clips would 30 turns pick up? Write the number.
8
Name one everyday use of an electromagnet. Accept any one: a scrapyard crane, an electric bell, or a relay.
9
Name the three factors that increase the strength of an electromagnet. Write the words.
10
Explain why the field lines of a current-carrying wire form circles. Write one sentence. Accept any sentence saying the field is round the wire, so the lines are circles around it.

Total 19 marks. Allow about 19 minutes.

Exercise 11X  Practice test questions

1
FDo unlike poles attract or repel? Write the word.[1 mark]
2
FWhich material keeps its magnetism when the field is removed: soft iron or steel? Write the word.[1 mark]
3
FWhere are field lines closest together around a bar magnet: at the poles, or in the middle? Write the word.[1 mark]
4
FName the remaining factor that increases the strength of an electromagnet, other than the iron core and the number of turns. Write the word. Accept current.[1 mark]
5
PSA coil picks up 4 clips at 0.5 A and 8 clips at 1 A, with 20 turns. Explain what happens to the strength when the current doubles. Write one sentence. Accept any sentence saying the strength doubles, because the number of clips doubles.[2 marks]
6
FDescribe the field pattern outside a bar magnet, in one sentence. Accept any sentence saying lines run from north to south, and are closer together at the poles.[2 marks]
7
RExplain why an iron nail becomes a magnet when a magnet is brought near it, but loses its magnetism when the magnet is removed. Write two sentences. Accept any answer saying the nail is an induced magnet, which is magnetised only in a field.[3 marks]
8
RA pupil wants a stronger electromagnet to pick up more clips. Name two changes she can make, and explain how each one helps. Write two sentences. Accept any two of: increase the current, add more turns, or add an iron core, with a reason that the field becomes stronger.[3 marks]
9
RExplain why a scrapyard crane uses an electromagnet rather than a permanent magnet. Write one sentence. Accept any sentence saying the electromagnet can be switched off to release the metal.[2 marks]
10
FName the force on a wire carrying a current in a magnetic field, and say how reversing the current affects its direction. Write two sentences. (Extension.) Accept any answer naming the motor effect, and saying reversing the current reverses the force.[3 marks]
← Chapter 10: Circuits, current, voltage and resistanceChapter 12: Pressure, forces and motion in depth →

Want a tutor to go through this chapter with your child?

Same tutor, same time, every week, live online. The first session is a free introduction.

💬 Book a Free Intro on WhatsApp
Chat on WhatsApp