Ch16 Magnetism

Question 1

Define bar magnet:

Answer 1

A rectangular shaped permanent magnet with a north pole at one end and the south pole at the other

Question 2

Give an example of a bar magnet:

Answer 2

Compass needle

Question 3

Give two rules about the forces between 2 bar magnets:

Answer 3

1) like poles ** repel**
2) unlike poles attract

Question 4

Define permanent magnet:

Answer 4

Magnetized magnetic material that produces its own magnetic field that does not get weaker with time

Question 5

Define hard (material):

Answer 5

A material act, once magnetized, is difficult to demagnetize

Question 6

Define soft (material):

Answer 6

The material that, once magnetized, is easy to demagnetize

Question 7

Give two examples of permanent magnets:

Answer 7

Ferrite
Hard steel

Question 8

What are ferrous materials?

Answer 8

Magnetic materials containing iron

Question 9

Define magnetized:

Answer 9

When a magnetic material has been made magnetic

Question 10

Define unmagnetised:

Answer 10

When a magnetic material has not been made magnetic

Question 11

Define induced magnetism:

Answer 11

When a magnetic material is only magnetised when placed in a magnetic field

(Ex, when brought close to the pole of a permanent magnet)

Question 12

Name three magnetic elements:

Answer 12

Iron, cobalt, nickel

Question 13

What is the difference between hard magnetic material and soft magnetic material?

Answer 13

Hard
→ retains magnetism well
→ difficult to magnetise in the first place

Soft
→ easy to magnetise
→ readily loses its magnetism.

Question 14

Give three uses for hard steel:

Answer 14

1) permanent magnets
2) compass needles
3) loudspeaker magnets

Question 15

Give three uses for soft iron:

Answer 15

1) cores for electromagnets
2) transformers
3) radio aerials

Question 16

Explain how magnets and magnetic materials and non-magnetic materials interact with each other:

Answer 16

Magnetic materials are attracted to magnets and they can become magnets themselves. non-magnetic materials do not interact with magnets

Question 17

What is a pole of a magnet?

Answer 17

Region on the magnet where the magnetic effect is the strongest

Question 18

Why are magnets called magnetic dipoles?

Answer 18

Because they have to poles → north and south

Question 19

Why can’t you create a magnetic ** monopole** by cutting a magnet in half?

Answer 19

It will just create a new magnet with both a north/suth Pole just weaker

Question 20

What regions do ferromagnetic materials consist of?

Answer 20

Small regions called domains
Each of which behaves like a small magnet with a north and south Pole

Question 21

How large are domains in ferromagnetic materials?

Answer 21

1 cm in length and width

Question 22

How does the direction in domains in an unmagnetised material look?

Answer 22

Domains in unmagnetised material have random overall direction

Question 23

How does the direction in domains in a magnet look?

Answer 23

Domains aligned overall in the same direction

Question 24

Name two methods to magnetise magnetic materials:

Answer 24

1) magnetising by stroking with a permanent magnet (or two)
2) magnetising by electric method

Question 25

Explain how you would magnetise a magnetic material by stroking it with a permanent magnet:

Answer 25

Magnet moves along rod → domains in material align in one overall direction → north/south Pole are induced at the two ends of the rod → gives rise to magnetic field

Question 26

How can a ferromagnetic material be magnetised by electric method?

Answer 26

It can be magnetised by placing it in a ** current-carrying solenoid**

Strong magnetic forces inside solenoid forces the domains in ferromagnetic material to align in the same direction as the magnetic field of the solenoid

Question 27

Define magnetic field:

Answer 27

A region of space around a magnet/electric current in which a magnetic pole experiences of force

Question 28

Define magnetic field lines:

Answer 28

Represent the direction the magnetic force would have on the north pole of a magnet

Question 29

Define plotting compass:

Answer 29

Very small compass with a needle that lines up with magnetic field lines, allowing changes in field direction to be observed and plotted over a very short distance

Question 30

What should you know if you are drawing the magnetic field lines around a single ball magnet?

Answer 30

→ direction: the direction of magnetic field line at any point is the direction of the force on the north pole of a magnet at that point
(Field lines come out of north poles and go in to South Pole)

→ strength: lines that are close together indicator strong field

Question 31

How can you define the direction of a magnetic field?

Answer 31

The direction that the north Pole of a compass needle would point if placed at that point

Question 32

State the rules on drawing magnetic field lines:

Answer 32

→** never cross**

→ do ** not** have a beginning more end

→ each magnetic field has a direction from north to south outside the magnet and south to north inside the magnet

→ the number of lines that we draw per unit represents the ** strength** of the magnet field in this area

Question 33

Define electromagnet:

Answer 33

A coil of wire that acts as a magnet when an electric current passes through it

Question 34

Define solenoid:

Answer 34

An electromagnet made by passing a current through a coil of wire

Question 35

What is a typical electromagnet made from?

Answer 35

Coil of copper wire

Question 36

Why is copper used for an electromagnet?

Answer 36

→ low resistance

Question 37

Why don’t you actually have to use a magnetic material for the coil in an electromagnet?

Answer 37

Because the whole point is that the electric current produces the magnetic field

Question 38

Give three ways to increase the strength of an electromagnet:

Answer 38

1) increase the current flowing through it
(Greater the current greater the field)

2) ** increase the number of terms of the wire on the coil**
(Packing more turns into the same space concentrates the field)

3) ** add a soft iron core**
(an iron core becomes strongly magnetised by the field and this makes the whole magnetic field much stronger

Question 39

What is the advantage of an electromagnet?

Answer 39

Switched on and off

Question 40

Give six uses for an electromagnet:

Answer 40

1) electromagnetic cranes
2) electric doorbells
3) loudspeakers
4) electric motors
4) relays
5) transformers

Question 41

What does it mean if the magnetic field inside of the electromagnet is uniform?

Answer 41

It means that the field lines are parallel and the same distance apart

Question 42

Describe the field around a solenoid:

Answer 42

→ field lines emerged from North Pole and go into South Pole

→ Field lines are closest together at the poles (strongest in this region)

→ The line spread out from the poles (weaker in these regions)

Question 43

Define conventional current:

Answer 43

The direction positive charges would flow in a complete circle, from the positive to negative terminals of a cell, and opposite to the direction that electrons flow

Question 44

What happens when you pass an electric current through a solenoid?

Answer 44

Produces a magnetic field

Question 45

What is an electromagnet:

Answer 45

A solenoid with an iron core in it

Question 46

What is an electromagnet:

Answer 46

A solenoid with an iron core in it

Question 47

What happens when you put a compass between two repelling bar magnets?

Answer 47

The compass will point to the geographical north, because in between the two repelling bar magnets, the net force is zero so the compass will not be influenced by it

Question 48

Define magnet:

Answer 48

Any material or object that produces a magnetic field

Question 49

What happens when you reverse the current of an electromagnetic magnet?

Answer 49

The poles will reverse