Magnetism

Question 1

What is meant by the ‘poles’ of a magnet?

Answer 1

The poles of a magnet are the places where the magnetic forces are strongest.

Question 2

What happens when two magnets are brought close together?

Answer 2

They exert a force on each other.

Question 3

Two like poles…

Answer 3

…repel each other.

Question 4

Two ______ poles attract each other.

Answer 4

unlike

Question 5

The attraction and repulsion between two magnetic poles is an example of what?

Answer 5

A non-contact force.

Question 6

Which direction do magnetic field lines go?

Answer 6

From the north (seeking) pole of a magnet to the south (seeking) pole of a magnet.

Question 7

What is a permanent magnet?

Answer 7

A magnet which produces its own magnetic field.

Question 8

What is an induced magnet?

Answer 8

A material that becomes a magnet when it is placed in a magnetic field.

Question 9

What does induced magnetism always cause?

Answer 9

A force of attraction.

Question 10

What happens when an induced magnet is removed from a magnetic field?

Answer 10

It loses most/all of its magnetism quickly.

Question 11

What is a magnetic material?

Answer 11

Any material or object that can be influenced by a magnetic
field, and has the potential to become a magnet.

Question 12

What is a magnetic field?

Answer 12

The region around a magnet where a force acts on another magnet or on a magnetic material.

Question 13

List the magnetic materials (at room temperature)

Answer 13

Iron
Steel (alloy of iron)
Cobalt
Nickel

Question 14

The force between a magnet and a magnetic material is always one of …

Answer 14

attraction

Question 15

What does the strength of a magnetic field depend on?

Answer 15

The distance from the magnet.

Question 16

Where is a magnetic field the strongest?

Answer 16

At the poles of a magnet.

Question 17

How do we work out the direction of a magnetic field at a particular point?

Answer 17

It is the same as the direction of the force that would act on another north pole placed at that point.

Question 18

Give examples of magnets

Answer 18

Bar magnet
Horseshoe magnet
Earth

Question 19

Does the Earth have a magnetic field?

Answer 19

Yes

Question 20

Explain how the behaviour of a magnetic compass is related to evidence that the core of the Earth must be magnetic.

Answer 20

-A magnetic compass contains a small bar magnet

-The compass needle (North) points in the direction of the Earth’s south magnetic pole (Northern hemisphere_
(-It does this with no other magnetic materials present)

-The Earth therefore must be magnetic

Question 21

Describe how to plot the magnetic field pattern of a magnet using a compass.

(1-7)

Answer 21

-Place a bar magnet in the middle of a piece of paper and draw around it

-Mark the north and south poles

-Place a plotting compass at the north pole

-Mark a dot in the direction that the pointer is facing

-Mark the tip with a dot

-Move the compass so the tail is on this dot and place another dot at the tip

-Repeat until back to the magnet at the south pole

Question 22

Explain how you can tell if a magnetic material is a permanent or induced magnet. [2]

Answer 22

Bring it near both poles of a known permanent magnet.

An induced magnetic material will always be attracted by a permanent magnet but a permanent magnet can be both attracted and repelled.

Question 23

Explain why unmagnetised iron is always attracted by a permanent magnet.

Answer 23

The permanent magnet always induces the opposite pole next to its pole, causing the unmagnetised iron to attract.

Question 24

What does a plotting compass contain?

Answer 24

A small bar magnet.

Question 25

Describe how to plot the magnetic field pattern of a magnet using a compass.

(8-10)

Answer 25

-Join the dots and add an arrow to show the direction of the field line

-Repeat from different starting positions around the poles to draw multiple field lines

Question 26

Why is using iron filings not a good way of showing a magnetic field?

Answer 26

They show the shape not the pattern of the magnetic field (i.e. the loops but not the direction).

Question 27

What happens when a current flows through a conducting wire?

Answer 27

A magnetic field is produced around the wire.

Question 28

What does the strength of a magnetic field around a conducting wire depend on?

Answer 28

-the current through the wire

-the distance from the wire

Question 29

What is a solenoid?

Answer 29

A coil of wire

Question 30

What can be done to increase the strength of the magnetic field created by a current through a wire?

Answer 30

Shaping the wire to form a solenoid.

Question 31

How do we describe the magnetic field inside a solenoid?

Answer 31

Strong and Uniform.

Question 32

What does the magnetic field around a solenoid have a similar shape to?

Answer 32

The magnetic field of a bar magnet.

Question 33

How can we increase the strength of the magnetic field of a solenoid?

Answer 33

Adding an iron core to form an electromagnet.

Question 34

What is an electromagnet?

Answer 34

A solenoid with an iron core.

Question 35

What is the motor effect?

Answer 35

When a conductor carrying a current is placed in a magnetic field the magnet producing the field and the conductor exert a force on each other.

Question 36

What does Fleming’s left hand rule represent?

Answer 36

The relative orientation of the force, the current in the conductor and the magnetic field.

Thumb = Thrust
First finger = Field
SeCond finger = Current

Question 37

Explain why the wire moves when the current is switched on.

Question 38

What are the factors that affect the size of the force on the conductor?

Question 39

Equation for a conductor at right angles to a magnetic field and carrying a current:

Answer 39

Force = magnetic flux density x current x length

F = B I L

Question 40

What is magnetic flux density?

Answer 40

A measure of how strong a magnet is.

1 Tesla is strong.

Question 41

Unit for magnetic flux density (B)?

Answer 41

Tesla, T