Magnetism

Question 0

What do magnetic field lines show 3

Answer 0

1) shape of magnetic field
2) direction (the field lines ‘travel’ from North to South)
3) the strength of the magnetic field - the field lines are closest together where the magnetic field is the strongest

Question 1

4 substances which exhibit magnetic properties

Answer 1

Iron
Steel
Nickel
Cobalt

Question 2

How can you tell if it’s a magnet

Answer 2

It repels another magnet

Question 3

The volume of space around every magnet where magnetism can be detected

Answer 3

The magnetic field

Question 4

What can we infer about magnets from placing one in a container full of iron filings

Answer 4

The shape of the magnetic field

It is strongest at its two poles - all the filings stick to the poles with very little elsewhere

Question 5

3 ways to increase the strength of the magnetic field around a solenoid

Answer 5

• increase the current through the coil
• increase the number of turns of wire per centimetre
• insert a piece of magnetic material (core) into the solenoid

Question 6

Advantages of electromagnet 2

Answer 6

Can be made as strong as required

Can be switched off when required

Question 7

What do the fingers represent on the left hand rule

Answer 7

Thumb=motion
1st finger=field
2nd finger = current

Question 8

If we pass a current through a piece of wire held at right angles to the magnetic field of a magnet, the wire will move. What is this movement caused by?

Answer 8

This motion is the result of a force created by overlapping magnetic fields around the wire and the magnet

Question 9

Purpose of the split ring commutator

Answer 9

Changes current direction every half turn

Question 10

What would happen if the commutator did not have a split in it?

Answer 10

The motor would rotate to vertical position and then vibrate until it came to rest

Question 11

What is electromagnetic induction?

Answer 11

The creation of a voltage (and maybe current) in a wire which is experiencing a change in magnetic field

Question 12

What is the Dynamo effect

Answer 12

Using electromagnetic induction to transform kinetic energy into electrical energy

Question 13

Why do transformers only work with ac currents and voltages?

Answer 13

Only work if the magnetic field around the primary coil is changing

Question 14

What is a transformer made from

Answer 14

A primary coil and a secondary coil wound on an iron core to concentrate the magnetic field in the coils

Question 15

Difference between step up and step down transformers

Answer 15

Step-up transformers increase the size of the output voltage by having more turns in the secondary coil than in the primary coil
Step-down transformers reduce the size of the output voltage by having fewer turns on the secondary coil than the primary coil

Question 16

Why is electricity transmitted through the national grid as alternating current rather than direct current

Answer 16

Transformers are needed to reduce current along power lines to decrease energy wasted and transformers only work with ac