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Physics Revision Notes

Leaving Cert Higher Level Physics

Chapter 5: Magnetism and Electromagnetism

These notes teach Magnetism and Electromagnetism clearly in simple English and then push into the deeper Higher Level reasoning. The aim is to build understanding first and exam confidence second.

Focus
Understanding before memorising
Interactive
Simulators and guided tools
Question Style
Worked examples, exam practice and teacher explanation
Format
Website reading and printable notes

Subtopics Covered

  • Chapter 5: Magnetism and Electromagnetism
  • Objectives
  • Exam-Ready Definitions
  • Concept Overview
  • Visual Learning Zone
  • Formula Toolbox

What This Pack Includes

  • Structured physics notes formatted for ExamsLogic website reading
  • Exam-focused diagrams, equations, and worked examples
  • Practical notes and mark scheme style guidance from the source files
  • Independent study guidance based on the official curriculum
  • Print-friendly layout for future PDF export when needed
Disclaimer
This publication is an independent educational resource developed by ExamsLogic and compiled by experienced educators. It is based on publicly available official curricula, including Cambridge, Pearson Edexcel, IB, and the Irish Leaving Certificate. This product is not endorsed by, affiliated with, or sponsored by any examination board or governing authority. All registered trademarks remain the property of their respective owners.

Chapter 5: Magnetism and Electromagnetism

1. Objectives

  • Describe magnetic poles, magnetic fields and how a compass behaves in a field.
  • Draw magnetic field patterns around bar magnets, straight wires and solenoids.
  • Use Fleming’s left-hand rule to predict force in the motor effect.
  • Explain electromagnetic induction using Faraday’s Law and Lenz’s Law.
  • Compare alternating current and direct current.
  • Use the transformer equation and explain why transformers only work with a changing current.

2. Exam-Ready Definitions

TermDefinition
Magnetic fieldA region where a magnetic pole or moving charge experiences a magnetic force.
Magnetic field lineA line showing the direction a north pole would move in a magnetic field.
ElectromagnetA temporary magnet produced by an electric current, usually using a coil and soft iron core.
Motor effectThe force on a current-carrying conductor placed in a magnetic field.
Electromagnetic inductionThe production of an emf/current when a conductor cuts magnetic field lines or experiences a changing magnetic field.
Faraday’s LawThe size of the induced emf is proportional to the rate of change of magnetic flux linkage.
Lenz’s LawThe induced current flows in a direction that opposes the change causing it.
TransformerA device that changes alternating voltage using electromagnetic induction between two coils.

3. Concept Overview

Magnetism begins with poles and fields. A magnet has a north and south pole, and unlike poles attract while like poles repel. Electromagnetism links electricity and magnetism: a current produces a magnetic field, and a changing magnetic field can produce a voltage. This is the big idea behind motors, generators and transformers.

4. Visual Learning Zone

Visual 1: Magnetic field around a bar magnet
NSOutside magnet: N → SCloser lines = stronger field
Exam rule: magnetic field lines point from north to south outside the magnet.
Visual 2: Field around a current-carrying wire
ICurrent produces circular magnetic field linesUse the right-hand grip rule: thumb = current, fingers = field direction.
This is the key diagram for wires, coils and electromagnets.
Visual 3: Motor effect — force on a current-carrying conductor
NSCurrent out of pageForceMagnetic field: N → S
Fleming’s left-hand rule links field, current and force. Reverse the current or field and the force reverses.
Visual 4: Electromagnetic induction
NSmove magnetGChanging magnetic fieldinduces emf/current
Faster movement, stronger magnet or more turns on the coil gives a larger induced emf.
Visual 5: Transformer — step-up and step-down
soft iron corePrimary coilSecondary coilfewer turnsmore turns → higher voltageOnly changing current produces changing magnetic flux, so transformers need a.c.
Step-up: secondary has more turns. Step-down: secondary has fewer turns.

5. Formula Toolbox

F = BIL
Force on conductor at right angles to field
Vp / Vs = Np / Ns
Transformer ratio
Vp Ip ≈ Vs Is
Ideal transformer power conservation
Induced emf ∝ rate of change of flux linkage
Faraday’s Law idea

Interactive Simulators

Teacher voice: Magnetism feels abstract until you connect it to devices. These tools keep the focus on what changes physically when you change the input.
Magnetism Tool 1
Transformer Ratio

Use the turns ratio to predict the secondary voltage.

Secondary voltage
60.00 V
Magnetism Tool 2
Electromagnet Strength Guide

Increase the values and see how a classroom electromagnet would usually become stronger.

Strength score
60
More turns and more current both make the electromagnet stronger.

6. Worked Examples

Example 1: Transformer voltage
A transformer has 500 turns on the primary and 2500 turns on the secondary. The primary voltage is 12 V. Find the secondary voltage.

Step 1: Vp / Vs = Np / Ns
Step 2: 12 / Vs = 500 / 2500
Step 3: Vs = 60 V
Final: This is a step-up transformer.
Example 2: Motor effect force
A wire of length 0.20 m carries a current of 4 A at right angles to a magnetic field of flux density 0.50 T. Find the force.

F = BIL = 0.50 × 4 × 0.20 = 0.40 N

7. Examiner Secrets

Secret 1: Field lines are not just decoration — their direction matters. Outside a bar magnet, they go N to S.
Secret 2: “Induced current opposes the change” is the key phrase for Lenz’s Law.
Secret 3: Transformers do not work with steady d.c. because there is no changing magnetic flux.
Secret 4: In motor-effect questions, say whether current or magnetic field was reversed if the force reverses.

8. Common Mistakes

1. Saying magnetic field lines start at south and end at north outside the magnet.
2. Forgetting that a current produces a magnetic field around a wire.
3. Saying induction happens just because a magnet is near a coil. The field must change or the conductor must cut field lines.
4. Using the transformer equation upside down.
5. Saying transformers work with d.c. without explaining the need for changing flux.

9. Examiner Traps

“Compass needle points…” → it aligns with the magnetic field direction.
“More turns on secondary” → step-up transformer if Ns > Np.
“Magnet held stationary inside coil” → no induced emf after the initial change.
“Current reversed” → force reverses in motor effect.
“Changing magnetic field” → electromagnetic induction.

10. Practical Skills

Experiment: Investigate electromagnetic induction
Connect a coil to a sensitive galvanometer. Move a bar magnet into and out of the coil. Observe the direction and size of the deflection. Move the magnet faster, use a stronger magnet, or increase the number of turns on the coil. A larger deflection shows a larger induced emf/current.

Precaution: Keep the motion along the axis of the coil and repeat readings to compare deflections fairly.

11. Exam Practice Questions

Q1. [6 marks] Draw the magnetic field pattern around a bar magnet and state the direction of the field lines.

Q2. [6 marks] A wire of length 0.30 m carries a current of 5 A in a magnetic field of 0.40 T. The wire is at right angles to the field. Calculate the force on the wire.

Q3. [8 marks] Explain electromagnetic induction and describe two ways to increase the induced emf in a coil.

Q4. [8 marks] A transformer has 200 turns on the primary coil and 1000 turns on the secondary coil. The primary voltage is 24 V. Calculate the secondary voltage and state whether the transformer is step-up or step-down.

12. MCQs with Explanations

1. Outside a bar magnet, magnetic field lines go:
A. south to north   B. north to south   C. clockwise only   D. from the centre outward

Answer: B. Outside the magnet, field lines leave the north pole and enter the south pole. A is the common trap.

2. A transformer requires alternating current because:
A. a.c. is safer   B. a.c. produces a changing magnetic field   C. d.c. has no energy   D. d.c. has no voltage

Answer: B. A changing magnetic field is needed to induce voltage in the secondary coil.

3. According to Lenz’s Law, the induced current:
A. supports the original change   B. opposes the change causing it   C. is always clockwise   D. exists only in magnets

Answer: B. This is the exact exam phrase to remember.

13. Higher-Level Challenge

A student says: “The magnet is inside the coil, so there must be a current.” Explain why this statement is incomplete. Your answer should refer to changing magnetic flux and the galvanometer reading.

14. Last-Minute Revision Sheet

If the exam is tomorrow, remember:
✓ Like magnetic poles repel; unlike poles attract.
✓ Field lines outside a magnet go from N to S.
✓ Current in a wire produces circular magnetic field lines.
✓ Motor effect: current + magnetic field → force.
✓ Induction needs changing magnetic field/flux.
✓ Lenz’s Law: induced current opposes the change causing it.
✓ Transformers need a.c., not steady d.c.
✓ Step-up transformer: more turns on secondary coil.
✓ Vp / Vs = Np / Ns.

15. Self-Assessment Checklist

  • I can draw magnetic field lines around a bar magnet.
  • I can use the right-hand grip rule for a current-carrying wire.
  • I can explain the motor effect and predict when force reverses.
  • I can describe electromagnetic induction using a coil, magnet and galvanometer.
  • I can state Faraday’s Law and Lenz’s Law in exam-ready language.
  • I can use the transformer equation correctly.

16. Mark Scheme

Q1:
Correct bar magnet with N and S poles. [1]
Curved field lines shown around magnet. [2]
Direction outside magnet from N to S. [2]
Field lines closer near poles. [1]

Q2:
F = BIL. [1]
F = 0.40 × 5 × 0.30. [3]
F = 0.60 N. [2]

Q3:
Induction is production of emf/current due to changing magnetic field/flux. [3]
Move magnet/coil faster. [2]
Use stronger magnet or more turns on coil. [2]
Correct reference to galvanometer deflection. [1]

Q4:
Vp / Vs = Np / Ns. [2]
24 / Vs = 200 / 1000. [2]
Vs = 120 V. [2]
Step-up because secondary turns and voltage are greater. [2]