IGCSE Co-ordinated Sciences · Area 3 · Physics

Electricity and Magnetism

Electricity and magnetism covers how charge is stored, moved and controlled: magnetism, charge, current, resistance and power, circuit diagrams, series and parallel circuits, electrical safety, induction, generators, motors and transformers.

Not started

Syllabus coverage

  • Describe the forces between magnetic poles and between magnets and magnetic materials, including the use of the terms north pole (N pole), south pole (S pole), attraction and repulsion, magnetised and unmagnetised
  • Describe induced magnetism
  • State the differences between the properties of temporary magnets, made of soft iron, and the properties of permanent magnets, made of steel
  • State the difference between magnetic and non-magnetic materials
  • Describe a magnetic field as a region in which a magnetic pole experiences a force
  • Draw the pattern and direction of magnetic field lines around a bar magnet
  • State that the direction of a magnetic field at a point is the direction of the force on the N pole of a magnet at that point
  • Describe the plotting of magnetic field lines with a compass or iron filings, and the use of a compass to determine the direction of the magnetic field
  • Describe the uses of permanent magnets and electromagnets
  • Explain that magnetic forces are due to interactions between magnetic fields, and know that the relative strength of a magnetic field is represented by the spacing of the magnetic field lines
  • State that there are positive and negative charges, that positive charges repel other positive charges, negative charges repel other negative charges, but positive charges attract negative charges
  • Describe simple experiments to show the production of electrostatic charges by friction and to show the detection of electrostatic charges
  • Explain that charging of solids by friction involves only a transfer of negative charge (electrons), describe an experiment to distinguish between electrical conductors and insulators, and recall and use a simple electron model to explain the difference, with typical examples
  • State that charge is measured in coulombs, describe an electric field as a region in which an electric charge experiences a force, and state that the direction of an electric field at a point is the direction of the force on a positive charge at that point
  • Describe simple electric field patterns, including the direction of the field, around a point charge, around a charged conducting sphere, and between two oppositely charged parallel conducting plates

Part of the IGCSE Co-ordinated Sciences syllabus 0654 / 0973.

The magnetic field around a bar magnetA magnetic field is a region in which a magnetic pole experiences a force. It is strongest at the poles.Field lines leave the N pole and curve round to the S poleClosest together at the polesFurther apart in the middleNSbar magnetEvery arrow on a field line points from the N pole to the S pole, because the direction of the field isthe direction of the force on a north pole placed there.The lines never cross, and they are closest together at the poles, where the field is strongest.
The magnetic field around a bar magnet: the field lines leave the N pole and curve round to the S pole, the lines are closest together at the poles where the field is strongest, and the arrows on the lines point from N to S.

Simple Phenomena of Magnetism

Magnets attract and repel each other and attract magnetic materials, and the region around a magnet where this force acts is its magnetic field. This topic covers the forces between magnetic poles, induced magnetism, temporary and permanent magnets, how to plot and read the magnetic field lines around a bar magnet, and the everyday uses of permanent magnets and electromagnets.

The magnetic field around a bar magnetA magnetic field is a region in which a magnetic pole experiences a force. It is strongest at the poles.Field lines leave the N pole and curve round to the S poleClosest together at the polesFurther apart in the middleNSbar magnetEvery arrow on a field line points from the N pole to the S pole, because the direction of the field isthe direction of the force on a north pole placed there.The lines never cross, and they are closest together at the poles, where the field is strongest.

Electrical Quantities

Electric charge is produced by friction and detected with an electroscope, and charges act on each other through an electric field. This topic covers charge and the electron model of conductors and insulators, electric fields, current and I = Q / t, e.m.f. and potential difference, resistance and current-voltage graphs, and electrical power and energy.

Electric Circuits

Circuits carry current along paths you can predict. This topic covers the symbols used to draw circuit diagrams, the rules for current and potential difference in series and parallel circuits, how to work out combined resistance and the combined e.m.f. of cells in series, and how a potential divider, a thermistor, an LDR, a diode and an LED behave in a circuit.

Electrical Safety

Mains electricity is dangerous because a current large enough to stop your heart can pass through your body. It covers the hazards of damaged insulation, overheating cables, damp conditions and overloading, the three wires of a mains circuit and why the switch belongs in the live wire, how fuses and trip switches protect the circuit, and why an appliance case must be earthed or double insulated.

Electromagnetic Effects

A changing magnetic field linking a conductor induces an e.m.f. in it. This topic covers electromagnetic induction and the factors that set the size and direction of the induced e.m.f., the a.c. generator, the magnetic field produced by a current, the force on a current-carrying conductor, the d.c. motor, and how transformers change voltage and make high-voltage transmission worthwhile.

Key terms you must be able to define

Magnetic field
A region in which a magnetic pole experiences a force. The field is strongest at the poles of a magnet and weakest far away from it.
Magnetic pole
An end of a magnet, where the magnetic effect is strongest. The north pole (N pole) is the end that points north when the magnet is free to turn, and the south pole (S pole) is the other end.
Induced magnetism
Magnetism produced in a magnetic material when it is placed in a magnetic field, without the magnet touching it. The end of the material nearest the magnet becomes an opposite pole, so the material is always attracted.
Magnetic material
A material that is attracted to a magnet, such as iron, steel, cobalt or nickel. Every other material, including copper and aluminium, is non-magnetic.
Temporary magnet
A magnet that is magnetic only while it is in a magnetic field, for example a piece of soft iron. Soft iron is easily magnetised and easily demagnetised.
Permanent magnet
A magnet that keeps its magnetism when the magnetising field is removed, for example a steel bar magnet or a compass needle. Steel is harder to magnetise but keeps its magnetism for a long time.
Magnetised
Having become a magnet, so that the material has its own north and south poles and can both attract and repel another magnet.
Unmagnetised
Not a magnet, so the material has no poles of its own. An unmagnetised magnetic material is still attracted to a magnet, by induced magnetism.
Electric charge
A property of matter that comes in two kinds, positive and negative; like charges repel and unlike charges attract. Charge is measured in coulombs (C).
Electric field
A region in which an electric charge experiences a force; its direction at a point is the direction of the force on a positive charge placed at that point.
Conductor
A material that contains free electrons able to move through it, so charge can flow; examples are copper, aluminium, silver, brass and graphite.
Electric current
The charge passing a point per unit time: I = Q / t. It is measured in amperes (A), where 1 A = 1 C/s.

Applied to the real world

Cambridge sets Co-ordinated Sciences in unfamiliar contexts - a hospital, a power station, a farm, a laboratory. Use these as models for how to apply the science, then write your own.

In a scrapyard

A crane carries a large electromagnet, which is a coil of wire wound on a soft iron core. When the current is switched on, the core becomes a strong magnet and picks up scrap steel. When the current is switched off, the soft iron loses its magnetism at once and the load falls cleanly. A permanent magnet could not do this job, because it could never let go of the load.

On a walk or at sea

A compass needle is a small steel magnet that is free to turn. The magnetic pole of the Earth near the geographic north is a magnetic south pole, so it attracts the north-seeking pole of the needle and the needle comes to rest pointing north-south. Steel is used rather than soft iron because the needle must stay magnetised with no power supply.

At home

A fridge magnet sticks to the steel door because the field induces an opposite pole in the steel, and unlike poles attract. The same idea keeps a magnetic door seal shut, holding a cupboard door or a freezer door closed. A magnet is not attracted to the aluminium of a drinks can, because aluminium is non-magnetic.

In a loudspeaker

A loudspeaker contains a permanent magnet with a coil of wire sitting in its field. When a changing current flows in the coil, the magnetic field of the coil interacts with the field of the permanent magnet, and the force on the coil makes it move. The coil is fixed to the cone, so the cone vibrates and produces the sound.

In a hospital

An MRI scanner uses a very strong electromagnet to produce a large, steady magnetic field around the patient. It has to be an electromagnet because a permanent magnet could not produce a field anywhere near as strong, and because the field must be switched off when the scanner is not in use. Nothing magnetic, such as a steel watch, may be taken into the room.

In a car

A car battery has an e.m.f. of 12 V, which means it transfers 12 J of energy to every coulomb of charge it pushes round the circuit. A headlamp rated at 60 W therefore draws a current of I = P / V = 60 / 12 = 5.0 A, and its resistance is R = V / I = 12 / 5.0 = 2.4 ohms. The battery's chemical store empties as it does this electrical work, and the lamp transfers the energy to its surroundings by heating and by light.

Flashcards

Click a card to flip it. Mark honestly — the tracker uses this.

Q1What happens when two like poles are brought close together?
They repel each other. Unlike poles attract each other.
Q2What is the only test that shows that two objects are both magnets?
Repulsion. Attraction happens between a magnet and any magnetic material, so on its own it proves nothing.
Q3Name four magnetic materials.
Iron, steel, cobalt and nickel.
Q4Why is an aluminium can not attracted to a magnet?
Aluminium is a metal, but it is non-magnetic, because its atoms cannot be lined up to form a magnet.
Q5What is induced magnetism?
Magnetism produced in a magnetic material when it is placed in a magnetic field, without the magnet touching it.
Q6Why is a piece of soft iron attracted to either pole of a magnet?
The field induces an opposite pole at the end nearest the magnet, and unlike poles attract.
Q7Give one difference between a temporary magnet of soft iron and a permanent magnet of steel.
Soft iron is easily magnetised and easily demagnetised, so it loses its magnetism when the field is removed; steel keeps its magnetism for a long time.
Q8Why is the core of an electromagnet made of soft iron?
Because soft iron magnetises quickly when the current is switched on and loses its magnetism at once when the current is switched off.
Q9What is a magnetic field?
A region in which a magnetic pole experiences a force.
Q10In which direction do the field lines run outside a bar magnet?
From the N pole to the S pole, forming closed curves that continue through the inside of the magnet from S back to N.
0 of 10 marked as known

Exam-style questions

9 questions, 28 marks. Write your answer, then reveal the mark scheme and tick each point you actually made. Answering honestly here is what makes the rest of the site useful.

StateAO11 mark
State what happens when the north pole of one bar magnet is brought close to the north pole of a second bar magnet.

Mark scheme — tick each point you actually made

Examiner tip: Name the poles in your answer. The mark is for repulsion between two like poles, so 'they push apart' on its own is too vague.
IdentifyAO12 marks
Identify two magnetic materials.

Mark scheme — tick each point you actually made

Examiner tip: Do not give aluminium or copper. They are metals, but they are non-magnetic, and a magnet does not attract them at all.
DescribeAO13 marks
Describe how iron filings are used to show the pattern of the magnetic field around a bar magnet.

Mark scheme — tick each point you actually made

Examiner tip: Say that the paper is tapped gently, not that the filings are stirred, and give the reason the filings line up: each one is magnetised by induction.
ExplainAO23 marks
A piece of unmagnetised soft iron is brought close to the north pole of a bar magnet and is attracted to it. Explain why the soft iron is attracted to the north pole.

Mark scheme — tick each point you actually made

Examiner tip: The words induced magnetism and opposite pole are the marks. Never say the iron already had a pole of its own, because the iron was unmagnetised.
CompareAO23 marks
Compare the properties of a temporary magnet made of soft iron with those of a permanent magnet made of steel.

Mark scheme — tick each point you actually made

Any 3 of these score full marks. The examiner only needs 3 distinct points - pick the ones you actually made.
Examiner tip: A comparison needs both sides of each point. Saying only what soft iron does is not a comparison, and each difference should be linked to the use that follows from it.
OutlineAO34 marks
Two identical metal bars look exactly the same. One is a permanent magnet and the other is a piece of soft iron. You are given a third bar that is known to be a magnet. Outline a test you could carry out to find out which of the two bars is the magnet, and explain why attraction on its own is not enough.

Mark scheme — tick each point you actually made

Any 4 of these score full marks. The examiner only needs 4 distinct points - pick the ones you actually made.
Examiner tip: Only repulsion is conclusive. Plan the test so that you use the same pole of the known magnet on every end, so that a repulsion result can be recognised at once.
ExplainAO24 marks
The magnetic field lines around a bar magnet are drawn close together at the poles and further apart in the space around the middle of the magnet. Explain what the spacing of the field lines shows about the magnetic field, and state the direction in which an arrow on a field line is drawn.

Mark scheme — tick each point you actually made

Examiner tip: Spacing means strength, not distance from the magnet. A wide gap between two lines means a weak field, and the lines must never be shown crossing.
CalculateAO23 marks
An electromagnet on a scrapyard crane holds a load of 250 kg stationary above the ground. Calculate the weight of the load, and state what the answer tells you about the force the electromagnet must exert. Use g = 10 N/kg.

Mark scheme — tick each point you actually made

Examiner tip: Give the unit N, not kg. The mass is 250 kg and the weight is 2500 N, and the two are different quantities linked by W = m x g.
SuggestAO25 marks
A scrapyard uses an electromagnet on a crane to move scrap steel, while a compass needle and a fridge magnet are permanent magnets. Suggest why an electromagnet is used on the crane, and why a permanent magnet is used for the compass needle.

Mark scheme — tick each point you actually made

Examiner tip: Justify each choice with the property that makes it suitable. For the crane, the two key ideas are switching the magnetism off and changing its strength.

Exam technique for this topic

  • Repulsion is the only test that proves two objects are both magnets. A magnet attracts any magnetic material as well as the opposite pole of another magnet, so an attraction result on its own proves nothing.
  • In every field-line answer, say that the arrows point from the N pole to the S pole and that the direction of the field is the direction of the force on a north pole placed there. Add that the lines never cross.
  • When you explain why a magnet attracts a piece of iron, use the words induced magnetism and opposite pole. Never write that the iron already had a pole of its own, because the iron was unmagnetised.
  • For soft iron and steel, always give the reason as well as the fact: soft iron magnetises and demagnetises easily, so it makes a temporary magnet; steel keeps its magnetism, so it makes a permanent magnet.
  • In a calculation, check which quantity is wanted. Mass is measured in kilograms and weight in newtons, and they are linked by W = m x g with g = 10 N/kg. Always write the unit with the answer.

Why students lose marks here

A student wroteA student wrote: 'A magnet will attract a copper coin because copper is a metal.'
Why it loses marksBeing a metal is not the same as being magnetic. Only iron, steel, cobalt and nickel are attracted to a magnet, and copper is not one of them, so no mark is scored for this answer.
The answer that scoresCopper is a metal, but it is non-magnetic, so a magnet does not attract it at all. The magnetic materials are iron, steel, cobalt and nickel. A magnet attracts these because their atoms behave like tiny magnets that can be lined up by the field, while the atoms of copper, aluminium and brass cannot be lined up in this way.
A student wroteA student wrote: 'A compass needle points north because the north pole of the Earth's magnetic field attracts the north pole of the needle.'
Why it loses marksTwo north poles would repel each other, not attract. The needle is a magnet, and only unlike poles attract, so the explanation is the wrong way round.
The answer that scoresThe compass needle is a small magnet that is free to turn. The magnetic pole of the Earth near the geographic north is a magnetic south pole, so it attracts the north-seeking pole of the needle. That is why the needle comes to rest pointing north-south, and why the end that points north is called the north pole of the magnet.
A student wroteA student wrote: 'Magnetic field lines are drawn from the south pole to the north pole, and they get further apart near the poles.'
Why it loses marksBoth parts are wrong. The direction of a field line is the direction of the force on a north pole, which takes the line from N to S, and the lines crowd together where the field is strongest, which is at the poles.
The answer that scoresOutside the magnet the field lines are drawn from the N pole to the S pole, because the direction of the field at a point is the direction of the force on a north pole placed there. The lines are closest together at the two poles and further apart in the space around the middle of the magnet, and the spacing of the lines shows the relative strength of the field.
North poleSouth poleMagnetic field linesPlotting compassThe field is strongest at the poles, where the field lines are closest together. A magneticfield line shows the direction a north pole would be pushed, so the arrows always point fromnorth to south outside the magnet.
A field pattern plotted with a plotting compass and with iron filings: the lines leave the N pole, curve round to the S pole, and are packed most tightly at the poles, where the field is strongest.
A student wroteA student wrote: 'A permanent magnet is used in a scrapyard crane because permanent magnets are the strongest kind of magnet.'
Why it loses marksStrength is not the reason, and a permanent magnet is not the strongest kind anyway. A permanent magnet cannot be switched off, so a crane fitted with one could never release the load it had picked up.
The answer that scoresThe crane uses an electromagnet, which is a coil of wire wound on a soft iron core. It can be switched on and off with the current, so the crane can pick up the scrap and then drop it, and its strength can be changed to suit the load. An electromagnet can also be made much stronger than any permanent magnet, because its strength increases with the current and with the number of turns of wire.
A scrapyard crane whose round lifting magnet is an electromagnet: the current holds the scrap steel on, and switching the current off releases it.

Where this fits in IGCSE Co-ordinated Sciences

This page is one topic of Cambridge IGCSE Co-ordinated Sciences 0654 / 0973. IGCSE Co-ordinated Sciences is the course home: every area and every topic in Cambridge's own order, the papers you sit and what each one tests, and the exam-practice tools. The full topic list, with each topic linked to its revision page, is on the IGCSE Co-ordinated Sciences syllabus page.