Simple Phenomena Of Magnetism

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Notes

Magnetism

Magnets have two **poles**: **north** and **south**.
Magnetic forces are **strongest at the poles**.
**Like poles repel** (N–N or S–S).
**Opposite poles attract** (N–S).
Attraction/repulsion between magnetic poles is a **non-contact force**.

Magnetic Materials

Only a few metals are magnetic: **iron**, **cobalt**, **nickel**.
**Steel** (an alloy containing iron) is also magnetic.
Magnetic materials are **attracted** to both poles of a magnet.
Non-magnetic materials (e.g., aluminium, plastic) are **not affected** by a magnet.
A material is a magnet if it **repels** a known magnet; it is magnetic if it **attracts**; non-magnetic if neither.

Permanent Magnets

Made from **hard magnetic materials** such as **steel**.
Produces its **own magnetic field**.
**Does not lose** its magnetism easily.
Used in: compasses, school lab magnets, toys, fridge magnets.

Induced (Temporary) Magnets

Made from **soft magnetic materials** such as **soft iron**.
Becomes magnetised only when placed in a magnetic field.
The end closest to the magnet gains the **opposite pole**.
**Loses magnetism quickly** when removed from the field.
Used in: electromagnets, transformers.

Magnetic Fields

A **magnetic field** is a region where a magnetic pole experiences a force.
Field lines go from **north pole to south pole**.
Arrows show direction of force on a north pole.
Field is **strongest at the poles** (lines are closer together).
Field **weakens with distance** (lines spread apart).

Plotting Magnetic Fields

**Iron filings method**: Place paper over magnet, sprinkle filings, tap gently to reveal field pattern.
**Plotting compass method**: Place compass near magnet, mark needle ends, move compass step by step to trace field lines.
Compass needle points from north to south (north arrow points to south pole of magnet).

Uses of Electromagnets

**MRI scanners** in hospitals use powerful electromagnets for imaging.
**Speakers and earphones** use electromagnets to produce sound.
**Recycling**: Electromagnets separate steel from other scrap.
**Mag-Lev trains** use repulsion between electromagnets to hover and reduce friction.

Magnetic field around a bar magnet: field lines from N to S, strongest at poles.

Practice questions

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1.Which of the following lists of metals contains only metals that are non-ferrous?
Easy
- AIron, steel, nickel
- BCobalt, copper, steel
- CAluminium, brass, copper
- DIron, tin, aluminium
2.Which metal is suitable for use as a permanent magnet?
Easy
- ASteel
- BSoft iron
- CCopper
- DAluminium
3.Which of the following lists contains only ferrous metals?
Easy
- AAluminium and iron
- BSteel and iron
- CSteel and lead
- DTin and iron
4.Which statement about a permanent bar magnet is incorrect?
Easy
- AThe S-pole attracts the N-pole of another magnet
- BThe S-pole repels the S-pole of another magnet
- CIt cannot repel a non-magnetic material
- DIt is made from a soft magnetic material (such as soft iron)
5.Which magnet has the strongest magnetic field?
Easy
- AA bar magnet with widely spaced field lines
- BA bar magnet with closely spaced field lines
- CA bar magnet with no field lines
- DA bar magnet with field lines that cross
6.What material can a temporary magnet be made from?
Easy
- APlastic
- BSoft iron
- CSteel
- DWood
7.Which compass correctly shows the direction of the magnetic field due to a bar magnet?
Easy
- AA compass with its north pole pointing towards the magnet's south pole
- BA compass with its north pole pointing towards the magnet's north pole
- CA compass with its south pole pointing towards the magnet's south pole
- DA compass with its needle aligned perpendicular to the magnet
8.Which of the following statements about a permanent bar magnet is true?
Medium
- AThe north pole of a permanent bar magnet will repel the north pole of another magnet.
- BA permanent bar magnet must be made from a soft magnetic material.
- CA permanent bar magnet can repel a magnetic material.
- DThe field lines of a permanent bar magnet cross each other where the field is strongest.

More questions

9.A student lines up some permanent magnets with soft iron nails in between. What would the magnetic poles of locations X and Y be? (Assume the north pole of a magnet is on the left and south on the right, with nails between magnets.)
Medium
- AX: north, Y: north
- BX: north, Y: south
- CX: south, Y: north
- DX: south, Y: south
10.Which of the following statements describes something a permanent magnet can do?
Medium
- AIt will repel non-magnetic materials.
- BIt will repel non-ferrous materials.
- CIt will attract ferrous materials.
- DIt will have a single magnetic pole.
11.Which test could be used to find which end of a magnet is the south pole?
Medium
- APutting it near a ferrous metal
- BPutting it near a compass needle and seeing whether the needle points towards the pole
- CPutting it near a compass needle and seeing whether the needle points away from the pole
- DPutting it near a non-ferrous metal
12.A student has two different materials. Material 1 magnetises easily and loses its magnetism as soon as it is removed from a magnetic field. Material 2 is difficult to magnetise but retains its magnetism for a long time. Which row shows the most suitable use for these materials?
Hard
- AMaterial 1: core of an electromagnet, Material 2: core of an electromagnet
- BMaterial 1: bar magnet, Material 2: bar magnet
- CMaterial 1: bar magnet, Material 2: core of an electromagnet
- DMaterial 1: core of an electromagnet, Material 2: bar magnet
13.A student sprinkles iron filings on a sheet of paper placed over a bar magnet and taps the paper gently. Which statement about the pattern formed by the iron filings is correct?
Medium
- AThe filings cluster at the poles and form lines that curve from north to south.
- BThe filings cluster at the centre and form straight lines from north to south.
- CThe filings spread evenly over the paper with no pattern.
- DThe filings form concentric circles around the magnet.
14.A student has a bar magnet and a metal bar. She brings the north pole of the magnet near one end of the metal bar. The metal bar is attracted to the magnet. She then brings the south pole of the magnet near the same end of the metal bar. What will happen?
Medium
- AThe metal bar will be repelled.
- BThe metal bar will be attracted.
- CThe metal bar will not move.
- DThe metal bar will rotate.
15.Two bar magnets are placed with their north poles facing each other, 5 cm apart. Which diagram best represents the magnetic field pattern between them?
Hard
- AField lines curving from one north pole to the other north pole.
- BField lines going straight from one north pole to the other north pole.
- CField lines spreading out from each north pole and curving away, with a neutral point in the middle.
- DField lines going from each north pole to the south pole of the same magnet only.
16.Which of the following is a non-magnetic metal?
Easy
- AIron
- BCobalt
- CNickel
- DCopper
17.A student uses a plotting compass to map the magnetic field around a bar magnet. At one point, the compass needle points towards the south pole of the magnet. What does this indicate about the direction of the magnetic field at that point?
Medium
- AThe field direction is towards the north pole.
- BThe field direction is towards the south pole.
- CThe field direction is away from the south pole.
- DThe field direction is parallel to the magnet.
18.An electromagnet is made by winding a coil of wire around a core and connecting it to a d.c. power supply. Which change would decrease the strength of the electromagnet?
Hard
- AIncreasing the number of turns on the coil.
- BIncreasing the current in the coil.
- CUsing a core made of steel instead of soft iron.
- DUsing a core made of soft iron instead of air.
19.A student hangs a metal bar from a thread and brings a bar magnet near it. The metal bar is attracted to the magnet. Which conclusion is correct?
Medium
- AThe metal bar must be a permanent magnet.
- BThe metal bar must be made of a magnetic material.
- CThe metal bar must be made of a non-magnetic material.
- DThe metal bar must have a north pole at the end near the magnet.
20.A student has four metal rods: W, X, Y, Z. She brings the north pole of a bar magnet near each end of each rod. Her results are: W attracts both ends, X repels one end and attracts the other, Y attracts both ends, Z shows no effect. Which rod(s) is/are permanent magnets?
Hard
- AW only
- BX only
- CY only
- DW and Y
21.The diagram shows a bar magnet placed under a sheet of paper. Iron filings are sprinkled on the paper and the paper is tapped. Which position on the paper has the strongest magnetic field?
Medium
- ADirectly above the centre of the magnet.
- BDirectly above the north pole of the magnet.
- CAt a point 5 cm from the north pole along the magnet's axis.
- DAt a point 5 cm from the centre perpendicular to the magnet.
22.Which material is most suitable for the core of an electromagnet that is switched on and off frequently?
Easy
- ASteel
- BSoft iron
- CCobalt
- DNickel
23.A student investigates the number of paper clips an electromagnet can pick up. She uses a soft iron core and a d.c. power supply. She varies the current and counts the clips picked up. Which graph best shows the relationship between current and number of clips?
Hard
- AA straight line through the origin.
- BA curve that increases and then levels off.
- CA curve that increases steadily.
- DA horizontal line.
24.A bar magnet is cut into two equal pieces perpendicular to its length. What happens to the magnetic poles of the pieces?
Medium
- AEach piece has only a north pole or only a south pole.
- BEach piece becomes a complete magnet with both a north and a south pole.
- CThe pieces lose their magnetism completely.
- DOne piece has two north poles, the other has two south poles.
25.A student uses a plotting compass to map the magnetic field around a bar magnet. She places the compass at point P and the north pole of the compass needle points towards the south pole of the magnet. What does this indicate about the direction of the magnetic field at point P?
Medium
- AThe magnetic field at P points towards the south pole of the magnet.
- BThe magnetic field at P points towards the north pole of the magnet.
- CThe magnetic field at P is perpendicular to the line joining P and the south pole.
- DThe magnetic field at P is zero.
26.A student wants to make an electromagnet that retains its magnetism after the power supply is switched off. Which combination of core material and power supply type should she use?
Hard
- ASoft iron core and a.c. supply
- BSteel core and a.c. supply
- CSoft iron core and d.c. supply
- DSteel core and d.c. supply
27.The diagram shows a bar magnet and four plotting compasses placed around it. Which compass correctly shows the direction of the magnetic field at its location?
Medium
- ACompass A
- BCompass B
- CCompass C
- DCompass D
28.A student has two unlabeled metal rods. She brings the north pole of a bar magnet near end X of rod 1. End X is attracted to the magnet. She then brings the north pole near end Y of rod 2. End Y is repelled by the magnet. What can she conclude?
Hard
- ARod 1 is a magnet and rod 2 is a magnetic material.
- BRod 1 is a magnetic material and rod 2 is a magnet.
- CBoth rods are magnets.
- DBoth rods are magnetic materials.
29.An unmagnetised soft iron bar is placed near the north pole of a strong permanent magnet. Which statement about the induced magnetism in the iron bar is correct?
Medium
- AThe end of the iron bar closest to the magnet becomes a north pole.
- BThe end of the iron bar closest to the magnet becomes a south pole.
- CThe iron bar becomes permanently magnetised.
- DThe iron bar is repelled by the magnet.
30.A student investigates the number of paper clips an electromagnet can pick up. She uses a soft iron core and a d.c. power supply. She varies the current and counts the paper clips picked up. Which graph best shows the relationship between current and number of paper clips?
Medium
- AA straight line through the origin with positive slope
- BA curve that increases and then levels off
- CA horizontal line
- DA curve that decreases
31.A student has four metal rods: W, X, Y, Z. She brings the north pole of a bar magnet near each end of each rod. Her results are: W attracts both ends, X repels both ends, Y attracts one end and repels the other, Z attracts both ends. Which rod is definitely a magnet?
Hard
- AW
- BX
- CY
- DZ
32.What is the definition of a magnetic field?
Easy
- AA region in which a magnetic pole experiences a force
- BA region where iron filings align
- CThe area around a magnet where it can attract paper clips
- DThe space between the poles of a magnet
33.A student uses the method of plotting compasses to draw magnetic field lines around a bar magnet. She places the compass at a point and marks the positions of the north and south ends of the needle. She then moves the compass so that the south end of the needle points to the previous north mark. Which statement about the direction of the field line is correct?
Hard
- AThe field line direction is from the north mark to the south mark.
- BThe field line direction is from the south mark to the north mark.
- CThe field line direction is perpendicular to the line joining the marks.
- DThe field line direction cannot be determined from this method.
34.Which of the following is a ferrous metal?
Easy
- AAluminium
- BCopper
- CSteel
- DBrass
35.A student places a bar magnet under a sheet of paper and sprinkles iron filings on top. After tapping the paper, the filings form a pattern. Which statement about the pattern is correct?
Medium
- AThe filings cluster at the poles where the field is strongest.
- BThe filings are evenly distributed across the paper.
- CThe filings form straight lines parallel to the magnet.
- DThe filings form circles around the magnet.
36.What are the two poles of a magnet called?
Easy
- ANorth and south
- BPositive and negative
- CEast and west
- DUp and down
37.Which of the following metals is magnetic?
Easy
- ACopper
- BAluminium
- CNickel
- DZinc
38.What is the direction of magnetic field lines outside a bar magnet?
Easy
- AFrom north to south
- BFrom south to north
- CFrom east to west
- DFrom west to east
39.A student brings the north pole of a bar magnet near one end of a metal rod. The rod is attracted to the magnet. Which conclusion is correct?
Medium
- AThe rod is definitely a magnet.
- BThe rod is definitely a magnetic material.
- CThe rod is definitely a non-magnetic material.
- DThe rod could be either a magnet or a magnetic material.
40.A bar magnet is cut into two equal pieces perpendicular to its length. Which statement about the pieces is correct?
Medium
- AEach piece has only one pole.
- BOne piece has a north pole only, the other has a south pole only.
- CEach piece becomes a complete magnet with both north and south poles.
- DBoth pieces lose their magnetism completely.

Slides

Magnetism and Magnetic Poles

The ends of a magnet are called poles.
Every magnet has a north pole and a south pole.
Magnetic forces are strongest at the poles.
Like poles repel, opposite poles attract.

What happens when the north pole of one magnet is brought near the north pole of another magnet?

They attract
They repel
Nothing
They become demagnetised

Magnetic Materials

Only a few metals are magnetic: iron, cobalt, nickel.
Steel is an alloy containing iron, so it is also magnetic.
Magnetic materials are attracted to a magnet regardless of which pole is used.
Non-magnetic materials (e.g., aluminium, plastic) are not attracted.

The three magnetic metals are ____, ____, and ____.

Permanent and Induced Magnets

Permanent magnets (e.g., steel) produce their own magnetic field and do not lose magnetism.
Induced (temporary) magnets (e.g., soft iron) become magnetic only in a magnetic field.
Induced magnetism always causes attraction between the magnet and the material.
When removed from the field, soft iron loses its magnetism quickly.

Which of these are true about induced magnets?

They are made from soft iron.
They remain magnetic permanently.
They attract the permanent magnet.
They can be made from plastic.

Magnetic Fields

A magnetic field is a region where a magnetic pole experiences a force.
Field lines go from north to south pole.
The field is strongest at the poles, where lines are closest.
The field weakens as distance from the magnet increases.

Where is the magnetic field strongest around a bar magnet?

At the centre
At the poles
Far away from the magnet
Equally everywhere

Plotting Magnetic Fields

Method 1: Place paper over magnet, sprinkle iron filings, tap to reveal field lines.
Method 2: Use a plotting compass: mark dots along the needle direction, join to form a line.
Field lines are drawn from north to south pole.

Iron filings align along the ____ lines when sprinkled on paper over a magnet.

Uses of Magnets

Permanent magnets: compasses, fridge magnets, toys, school experiments.
Electromagnets: MRI scanners, speakers, recycling, Mag-Lev trains.

Which of these are uses of electromagnets?

MRI scanners
Fridge magnets
Recycling scrap metal
Compasses

Testing Materials with a Magnet

If a material is repelled by a known magnet, it is a magnet.
If attracted, it is a magnetic material (not necessarily a magnet).
If neither attracted nor repelled, it is non-magnetic.

A metal bar is attracted to both poles of a magnet. What can you conclude?

It is a permanent magnet
It is a magnetic material
It is non-magnetic
It is an electromagnet

Induced Magnetism Polarity

When a magnetic material is placed near a magnet, the end closest becomes the opposite pole.
This always causes attraction between the magnet and the material.

The north pole of a magnet is brought near a soft iron bar. What pole is induced at the near end of the bar?

North
South
No pole
Both poles

Magnetic Field Strength and Spacing

Closer field lines indicate a stronger field.
Further apart lines indicate a weaker field.
This is used to show the field strength in diagrams.

Where magnetic field lines are ____, the field is stronger.

Summary

Magnets have north and south poles; like poles repel, opposites attract.
Magnetic materials: iron, cobalt, nickel, steel.
Permanent magnets retain magnetism; induced magnets lose it quickly.
Field lines go from north to south; strength shown by line spacing.

Which material is best for the core of an electromagnet?

Steel
Soft iron
Aluminium
Copper

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