5. Magnetism

Question 1

State the Properties of Magnets

Answer 1

1. Magnets attract magnetic materials (cobalt, iron, nickel, steel).
2. Magnets have two poles.
3. A freely suspended magnet comes to rest in the north-south direction.
4. Like poles repel, unlike poles attract.

Question 2

What is magnetic induction?

Answer 2

Magnetic induction is the process whereby an object made of a magnetic material becomes an induced magnet when it is placed close to or in contact with a strong magnet or within a current-carrying solenoid.

Question 3

Describe magnetising by stroking

Answer 3

1. An unmagnetised steel bar is stroked several times from one end to the other, in one direction, with one of the poles of the permanent magnet.
2. The stroking magnet should be lifted sufficiently high above the steel bar between successive strokes.
3. The end of the steel bar where the strokes finish is induced with a pole opposite to the stroking pole used.

Question 4

Describe magnetising by electrical method

Answer 4

1. When a large direct current flows through a solenoid, a strong magnetif field is produced.
2. The magnetic field aligns the ‘tiny magnets’ in the steel bar.
3. After a period of time, the steel bar will be magnetised.

Question 5

Describe demagnetising by heating

Answer 5

Strongly heating a magnet and letting it cool in an east-west direction will cause the magnet to lose its magnetism. The atoms of the magnet vibrate vigorously whn heated, cuasing the ‘tiny magnets’ within the magnet to lose their alignments.

Question 6

Describe demagnetising by hammering

Answer 6

Hammering a magnet placed in the east-west direction alters the alignment of the ‘tiny magnet’s within the magnet, causing the magnet to lose its magnetism

Question 7

Describe demangetising by electrical method

Answer 7

1. Place a megnet inside a solenoid in the east-west direction.
2. Connect he solenoid to an alternating current supply.
3. Withdraw the magnet with the alternating current still flowing in the solenoid until it is some distance away.

Question 8

Magnetic Field

Definition

Answer 8

A magnetic field is a region in which the force of magnetism acts.

It can be revealed by sprinkling iron filings around a magnet or by using a compass.

Question 9

Soft Magnetic Materials

Properties + Example + Used to make + Application

Answer 9

Properties: easy to magnetise and demagnetise
Example: iron
Used to make: temporary magnets
Application: electromagnets, magetnic relay, electric bell

Question 10

Hard Magentic Materials

Properties + Example + Used to make + Application

Answer 10

Properties: difficult to magnetise and demagnetise
Example: steel
Used to make: temporary magnets
Application: magnetic door catch, loudspeaker, moving coil ammeter

Question 11

Temporary Magnets vs Permanent Magnets

Answer 11

Temporary magnets are magnets that retain their magnetism in the presence of an electric current or a permanent magnetic field.
Permanet magnets do not require the presence of an electric current or a permanent magnetic field to retain their magnetism.