Simple Phenomena OF Magnetism — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions

Section 1 of 21Poles and forces

Poles

• Poles the ends of a magnet are a north pole and a south pole, where the force is strongest

Like poles

• Like poles repel each other

Unlike poles

• Unlike poles attract each other

Non-contact force

• Non-contact force attraction or repulsion between poles acts without touching

Section 2 of 21Magnetic materials

Magnetic metals

• Magnetic metals iron, cobalt and nickel, and steel because it contains iron

Attraction

• Attraction magnetic materials are attracted to both poles of a magnet

Test with a known magnet

• Repelled means the object is a magnet
• Attracted means a magnetic material
• Neither means non-magnetic

Section 3 of 21Types of magnet

Types of magnet

Permanent magnet

• Permanent magnet made of a material such as steel, has its own field and does not lose its magnetism

Induced (temporary) magnet

• Induced (temporary) magnet a material such as soft iron that becomes a magnet while in a magnetic field

Induced poles

• Induced poles the end nearest the magnet becomes the opposite pole, so there is always attraction

Losing magnetism

• Losing magnetism soft iron loses induced magnetism quickly when removed, steel objects such as paperclips remain magnetised for a while

Section 4 of 21Uses

Permanent magnets

• Permanent magnets compasses, school experiments, toy trains and fridge magnets

Electromagnets

• MRI scanners
• Loudspeakers, microphones and earphones
• Separating steel for recycling
• Mag-Lev trains

Section 5 of 21Magnetic fields

Magnetic field

• Magnetic field a region in which a magnetic pole experiences a force

Field lines

• Field lines run from the north pole to the south pole with arrows showing the direction of the force

Strength

• Strength strongest at the poles, where field lines are closest together, and weaker with distance

Section 6 of 21Plotting a field

Iron filings

• Iron filings sprinkle on paper over a magnet, tap, and they settle on the field lines

Plotting compass

• Plotting compass mark dots at the ends of the needle, move the compass along and join the dots in a smooth curve

Direction

• Direction the north end of the compass points along the field, from north pole to south pole

Section 7 of 21More from the specification

More from the specification

Magnetic poles

• A bar magnet has a north and south pole;
  • like poles repel (move apart) and unlike poles are attracted towards each other.

Magnetic forces

• Forces act at a distance and are strongest at the poles;
  • they act on magnetic materials such as iron, steel, cobalt and nickel.

Test for a magnet

• Only repulsion proves a magnet, because a magnetic material is also attracted by a magnet.

Plotting compass

• A freely suspended piece of magnet aligns with the Earth's field, pointing north, and shows field direction.

Induced magnetism

• A magnetic material placed near a magnet becomes a temporary magnet, and soft iron loses it easily.

Magnetic poles

• A bar magnet has a north and south pole;
  • like poles repel (move apart) and unlike poles are attracted towards each other.

Magnetic forces

• Forces act at a distance and are strongest at the poles;
  • they act on magnetic materials such as iron, steel, cobalt and nickel.

Test for a magnet

• Only repulsion proves a magnet, because a magnetic material is also attracted by a magnet.

Plotting compass

• A freely suspended piece of magnet aligns with the Earth's field, pointing north, and shows field direction.

Induced magnetism

• A magnetic material placed near a magnet becomes a temporary magnet, and soft iron loses it easily.

Magnetic force

• The force on a moving charge in a magnetic field

Section 8 of 21Poles and the law of magnetism

Poles

• Poles the ends of a magnet are called its poles, and every magnet has one north pole and one south pole.
• Magnetic forces are strongest at the poles.
• Cutting a magnet in two never isolates a single pole; each piece has its own north and south.

Like poles repel

• Like poles repel a north pole pushes a north pole away, and a south pole pushes a south pole away.
• Two magnets pushing apart show repulsion.

Opposite poles attract

• Opposite poles attract a north pole is pulled towards a south pole.
• Two magnets pulling together show attraction.

Non-contact force

• Non-contact force the push or pull between poles acts across a gap without the magnets touching.
• This is why a magnet can move a paper clip through the air or hold up a hovering train.

Exam skill

• Exam skill you must predict the interaction when given the arrangement of magnets.
• Identify the two facing poles first, then apply: same = repel, different = attract.

Section 9 of 21Magnetic and non-magnetic materials

Magnetic metals

• Magnetic metals very few metals are magnetic: iron, cobalt and nickel.
• Steel is an alloy containing iron, so it is magnetic too.
• Aluminium, copper and most other metals are non-magnetic.

Attracted to both poles

• Attracted to both poles a magnetic material that is not itself a magnet is attracted to either pole of a magnet.
• This is different from a magnet, which can be attracted or repelled depending on the pole.

Section 10 of 21Testing an unknown object with a known magnet

Observation	Conclusion
Attracted by both ends of the known magnet	Magnetic material (not a magnet)
Repelled by one pole of the known magnet	It is a magnet (only repulsion proves this)
Neither attracted nor repelled	Non-magnetic material

Section 11 of 21Permanent and induced magnets

1Permanent magnet

• Permanent magnet made of a permanent magnetic material such as steel, it produces its own magnetic field and does not lose its magnetism.

2Induced (temporary) magnet

• Induced (temporary) magnet a magnetic material, such as soft iron, that becomes a magnet only while it is in a magnetic field.
• When it is removed from the field it loses its magnetism quickly and becomes unmagnetised.

3Induction always attracts

• Induction always attracts the end of the material nearest the magnet becomes the opposite pole to the magnet pole nearest it.
• A north pole brought near iron induces a south pole at the near end, so they attract.

4Steel versus soft iron

• Steel versus soft iron steel objects such as paper clips and needles can stay magnetised for a while.
• Soft iron used in electromagnets and transformers is unmagnetised as soon as the cause of the induction is removed.

Section 12 of 21Uses of permanent magnets and electromagnets

Permanent magnets

• Permanent magnets used in compasses, school experiments, toys such as magnetic train couplings, and fridge magnets.
• A compass needle always points north, which is why compasses have been used for navigation for thousands of years.

Electromagnets

• Electromagnets used in MRI scanners, loudspeakers, microphones and earphones.
• An MRI scanner uses powerful electromagnets to produce images of the organs of the body.

Recycling

• Recycling electromagnets pick up and sort steel from other metals and materials.
• Recovered steel is re-used, which reduces the mining of iron ore.

Mag-Lev trains

• Mag-Lev trains large electromagnets on the train and track repel each other so the train hovers above the rails.
• This removes friction and allows speeds of nearly 640 km/h.

Section 13 of 21More from the specification

1Magnetic Fields and Field Lines

• A magnetic field is a region where a magnetic material or moving charge experiences a non-contact magnetic force;
  • magnetic field lines point from the north pole to the south pole outside the magnet.

2Mapping Magnetic Fields with Iron Filings

• Sprinkling fine iron filings over paper placed above a bar magnet and tapping lightly causes the filings to align along invisible magnetic field lines, revealing field shape and pattern.

3Plotting Field Lines with a Compass

• Placing a small plotting compass at different locations near a magnet and plotting successive needle directions maps out continuous magnetic field lines with accurate arrow direction.

4Field Strength and Suspended Magnets

• The closeness of magnetic field lines indicates local magnetic field strength; a freely suspended bar magnet aligns itself with Earth's geomagnetic field lines.
  • (strongest close to the poles)

5Magnetic field orientation

• Magnetic field orientation external flux lines emerge outward from magnetic north and loop continuously towards the southern pole.

6Plotting magnetic fields

• Plotting magnetic fields moving a small plotting compass from pole to pole maps curved magnetic field lines with high precision.

7Iron filings pattern

• Iron filings pattern sprinkling iron filings over cardboard reveals field line spacing, showing strongest fields where lines are close together.

8Field lines

• Lines showing the direction and strength of a magnetic field.

Section 14 of 21What a magnetic field is

Definition

• Definition a magnetic field is a region in which a magnetic pole experiences a force.
• Magnets and current-carrying wires both create magnetic fields.

Field lines

• Field lines lines drawn to show the direction and strength of the field.
• They always carry an arrow and run from the north pole to the south pole outside the magnet.

Direction

• Direction the arrow on a field line shows the direction in which the force on a north pole would act.
• A free north pole would be pushed away from a north pole and pulled towards a south pole.

Section 15 of 21Field around a bar magnet

Field around a bar magnet

Strongest at the poles

• Strongest at the poles the field lines are closest together at the ends of the magnet.

Weaker with distance

• Weaker with distance the lines spread further apart as you move away from the magnet.

Strength shown by spacing

• Strength shown by spacing closely spaced lines mean a strong field and widely spaced lines mean a weak field.

Lines never cross

• Lines never cross at any point the field has only one direction.

Two magnets

(Extended) — forces between magnets are interactions between their fields.

• In attraction, lines run from the north pole of one magnet straight into the south pole of the other.
• In repulsion, the lines from the two facing poles bend away from each other with a gap between them.

Section 16 of 21Drawing a field correctly

Arrows

• Arrows add arrows pointing away from the north pole and towards the south pole.

Spacing

• Spacing draw the lines closer at the poles and further apart away from the magnet.

Smooth curves

• Smooth curves draw continuous curves from the north pole round to the south pole, not straight or broken lines.

Section 17 of 21Plotting with iron filings

1

Place a sheet of paper on top of the magnet.

2

Sprinkle iron filings gently over the paper.

3

Tap the paper lightly so the filings settle along the field lines.

4

Each filing is magnetised by induction and behaves like a tiny compass.

• The pattern shows the shape and strength of the field, but not its direction.

Section 18 of 21Plotting with a plotting compass

1

Place the magnet on a sheet of paper and draw a dot beside one end, near its corner.

2

Put the plotting compass so that one end of the needle points at the dot.

3

Draw a new dot at the other end of the needle.

4

Move the compass so the first end of the needle sits on the new dot, and repeat.

5

Continue until a chain of dots runs from one pole to the other.

6

Remove the compass and join the dots with a smooth curve to make one field line.

7

Mark the direction: the north end of the compass needle points along the field, from the north pole of the magnet towards the south pole.

8

Repeat from different starting points to draw more field lines.

• Why use both methods
  • filings show the overall pattern quickly while the compass gives the direction.

Section 19 of 21More from the specification

More from the specification

Magnetic poles and field properties

• Opposite magnetic poles attract while like poles repel;
  • magnetic field lines point from North to South outside a magnet.

Hard vs soft magnetic materials

• Soft iron is easily magnetised and demagnetised, ideal for temporary electromagnet cores;
  • hard steel retains magnetism permanently.

Magnetic field around electric currents

• An electric current flowing through a straight wire produces concentric circular magnetic field lines, whose direction is given by the right-hand grip rule.

Magnetic attraction and repulsion

• Magnetic attraction and repulsion like magnetic poles repel each other, while unlike opposite poles experience mutual magnetic attraction.

Permanent versus temporary magnets

• Permanent versus temporary magnets hard magnetic materials like steel form permanent magnets, while soft iron forms temporary electromagnets.

Ferromagnetic metals

• Ferromagnetic metals iron, cobalt, and nickel are ferromagnetic materials strongly attracted to permanent magnets.

Permanent magnet

• Magnet whose field is always there.

Magnetic material

• Material attracted to a magnet.

Electromagnet

• Magnet made by current through a coil around a magnetic core.

Section 20 of 21Key terms

Term	Meaning
Pole	End of a magnet where the magnetic force is strongest
Induced magnet	Material temporarily magnetised in a magnetic field
Magnetic field	Region in which a magnetic pole experiences a force
Field line	Line showing the direction of the force on a north pole
Permanent magnet	Magnet that keeps its magnetism

Term	Meaning
Pole	An end of a magnet where the magnetic force is strongest.
Law of magnetism	Like poles repel and opposite poles attract.
Magnetic material	A material such as iron, cobalt, nickel or steel that is attracted to a magnet.
Permanent magnet	A magnet made from a material like steel that keeps its magnetism and its own field.
Induced magnet	A magnetic material that is temporarily magnetised while in a magnetic field.
Electromagnet	A magnet made from a coil with a soft iron core that works only while current flows.
Non-contact force	A force that acts between objects without them touching.

Term	Meaning
Magnetic field	A region in which a magnetic pole experiences a force.
Field line	A line showing the direction of the force on a north pole in the field.
Plotting compass	A small compass used to find the field direction at a point.
Iron filings	Tiny iron pieces that become magnetised and line up with the field.
Field strength	How strong the field is, shown by how close together the field lines are.
Bar magnet	A rectangular permanent magnet with a pole at each end.

Section 21 of 21Exam technique

1

Saying attraction proves an object is a magnet — only repulsion does.

2

Saying like poles attract — like poles repel and unlike poles attract.

3

Drawing field lines going south to north — they go from north to south outside the magnet.

4

Drawing field lines that cross — the field has one direction at each point.

1

Thinking attraction proves an object is a magnet — only repulsion proves it; attraction also happens with unmagnetised iron, steel, cobalt or nickel.

2

Saying all metals are magnetic — only iron, cobalt, nickel and steel are, while aluminium and copper are not.

3

Believing induced magnetism can repel — induction always produces attraction between the magnet and the induced magnet.

4

Forgetting that steel is magnetic — steel is an iron alloy and is attracted to magnets.

1

Drawing field lines with no arrows — every line must show direction from north to south.

2

Letting field lines cross or stop in space — they are continuous curves that never cross.

3

Saying iron filings show the direction of the field — they only show shape and strength; use a compass for direction.

4

Drawing lines equally spaced everywhere — they must be closer together at the poles.