P7

Question 1

What is are the poles of a magnet?

Answer 1

• The poles of a magnet are the places where the magnetic forces are strongest
• When two magnet are brought close together. They exerts a force on each other
• Two like poles repel each other
• Two unlike poles attract each other
• Attraction and repulsion between two magnetic poles are examples of a non-contact force

Question 2

What are the two types of magnets?

Answer 2

Permanent and induced magnets

Question 3

Characteristics of a permanent magnet

Answer 3

A permanent magnet produces its own magnetic field

Question 4

Characteristics of induced magnets

Answer 4

• Induced magnets are magnetic materials that turn into a magnet when they’re put into a magnetic field
• When you take away the magnetic field, induced magnets quickly lose their magnetism (or most of it) and stop producing a magnetic

Question 5

What are permanent and induced magnets when they are together?

Answer 5

The forces are always attractive

Question 6

What is the magnetic field?

Answer 6

A region where other magnets or magnetic materials (e.g. iron, steel, nickel and cobalt) experience a non-contact force

Question 7

How can you show a magnetic field?

Answer 7

By drawing magnetic field lines

Question 8

What is always one force of attraction?

Answer 8

The force between a magnet and a magnetic material

Question 9

What does the strength of a magnetic field depend on and where is it strongest?

Answer 9

• The strength of the magnetic field depends on the distance from the magnet
• The field is the strongest at the poles of a magnet

Question 10

Where is the direction of the magnetic field?

Answer 10

• It is given by the direction of the force that would act on another North Pole placed at that point
• The direction of the magnetic field lines from the north (seeking) pole of a magnet to the south (seeking) pole of the magnet

Question 11

What does a magnetic compass contain?

Answer 11

• Magnetic compass contains a small bar magnet
• The Earth have a magnetic field, the compass needle points in the direction of the earths magnetic field

Question 12

How do you plot the magnetic field pattern of a magnet using a compass?

Answer 12

1) Place the plotting compass near the magnet on a piece of paper
2) Mark the direction the compass needle points
3) Move the plotting compass to many different positions in the magnetic field, marking the needle direction each time
4) Join the points to show the field lines

Question 13

How do you draw the magnetic field pattern of a bar magnet showing how strength and direction change from one point to another?

Answer 13

The diagram shows these key features:

• The magnetic field lines never cross each other
• The closer the lines, the stronger the magnetic field
• The lines have arrowheads to show the direction of the force exerted by a magnetic north pole
• The arrowheads point from the north pole of the magnet to its south pole

Question 14

How is the behavoir of a magnetic compass is related to evidence that the core of the Earth must be magnetic?

Answer 14

• The behaviour of a compass shows that the Earth has a magnetic field which means that the core of the Earth must be magnetic
• Scientists believe that this field is produced by convection currents in the Earth’s core, which is made from iron and nickel

Question 15

When a current flows through a conducting wire, what is created?

Answer 15

A magnetic field is created around the wire

Question 16

How can the strength of the magnetic field change?

Answer 16

• The strength of the magnetic field produced changes with the current and the distance from the wire
• The larger the current through the wire, or the closer to the wire you are, the stronger the field is.

Question 17

What is a solenoid?

Answer 17

A coil of wire

Question 18

When you shape of a wire to form a solenoid what does it do?

Answer 18

• It increases the strength of the magnetic field created by a current through the wire
• The magnetic field inside a solenoid is strong and uniform

Question 19

What does adding an iron core to a magnetic field do?

Answer 19

• The magnetic field around a solenoid has a similar shape to that of a bar magnet
• Adding an iron core increases the strength of the magnetic field of a solenoid
• An electromagnet is a solenoid with an iron core

Question 20

How can the magnetic effect of a current be demonstrated?

Answer 20

• When a current flows in a wire, it creates a circular magnetic field around the wire
• This magnetic field can deflect the needle of a magnetic compass
• The strength of the magnetic field is greater: closer to the wire

Question 21

Note:

Answer 21

AQA says that students should be able to draw the magnetic field pattern for a straight wire carrying a current snd for a solenoid ( showing the direction of the field)

Question 22

What is the motor effect?

Answer 22

• When a current-carrying wire (or any other conductor) is put between magnetic poles, the magnetic field around the wire interacts with the magnetic field it has been placed in
• This causes the magnet and the conductor to exert a force on each other
• This is called the motor effect and can cause the wire to move

Question 23

How do you find the direction of the force?

Answer 23

Fleming left-hand rule

Question 24

State the steps for Fleming’s left hand rule

Answer 24

1) Using your left hand, point your First finger in the direction of the magnetic Field
2) Point your second finger in the direction of the Current
3) Your thumb will then point in the direction of the force (Motion)

Question 25

What does Fleming’s left hand rule demonstrate?

Answer 25

Fleming’s left-hand rule shows that if either the current or the magnetic field is reversed, then the direction of the force will also be reversed

Question 26

How does Fleming’s left hand rule represent the relative orientation of the force, the current in the conductor and the magnetic field?

Answer 26

• The forefinger is lined up with magnetic field lines pointing from north to south
• The second finger is lined up with the current pointing from positive to negative
• The thumb shows the direction of the motor effect force on the conductor carrying the current

Question 27

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

Answer 27

Current: The larger the current, the larger the force
Length: The longer the length of the conductor, the larger the force
Magnetic Flux Density: The higher the density, the more magnetic field lines and the larger the force on the conductor

Question 28

How do you find the force?

Answer 28

Force(N) = Magnetic flux density(T) x Current(A) x Length(m)

F = BII

Question 29

What is the basis of an electric motor?

Answer 29

A Coil of wire carrying a current in a magnetic field tends to rotate

Question 30

How does the force on a conductor in a magnetic field causes the rotation of the coil in an electric motor?

Answer 30

• This is often when a current passes through a conductor as this generates a magnetic field
• This magnetic field interacts with a second magnetic field causing a force to be exerted
• The forces acting on a coil of wire in a magnetic field it will cause it to rotate
• This rotation is used inside an electric motor

When a current is passed through the coil, the coil spins, because the force on the left hand, side acts upwards and the force on the right hand side acts downwards.