Topic 7

Question 1

What do all magnets produce?

Answer 1

a magnetic field

Question 2

What is a magnetic field?

Answer 2

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

Question 3

What can magnetic field lines show?

Answer 3

magnetic field. the closer the lines are, the stronger the magnetic field. The further away from a magnet you get, the weaker the field line is.

Question 4

What part of the magnet has the strongest magnetic field.

Answer 4

the poles this means the magnetic forces are also strongest at the poles

Question 5

What happens if two poles of a magnet are put near each other?

Answer 5

they will exert a force on each other. two poles that are the same will repel each other. Two unlike poles will attract each other.

Question 6

What does a compass show?

Answer 6

the direction of the magnetic field

Question 7

What is inside a compass?

Answer 7

a tiny bar magnet. The north pole of a magnet is attracted to the south pole of any other magnet it is near. So the compass points in the direction of the magnetic field it is in

Question 8

What direction does a compass point to when it’s not near a magnet

Answer 8

north this is because the earth generates its own magnetic field, which shows the inside (core) of the earth must be magnetic.

Question 9

What are the different types of magnet?

Answer 9

permanent and induced magnets

Question 10

What is the difference between a permanent and induced magnet?

Answer 10

permanent magnets produce their own magnetic field. Induced magnets are magnetic materials that turn into a magnet when they’re put into a magnetic field.

Question 11

Describe the force between permanent and induced magnets?

Answer 11

always attractive

Question 12

What happens when you take away the magnetic field for an induced magnet?

Answer 12

the induced magnet will quickly loose their magnetism and stop producing a magnetic field

Question 13

What are examples of non-contact forces?

Answer 13

attraction and repulsion between two magnetic poles

Question 14

What is created when a current flows through a conducting wire?

Answer 14

a magnetic field around the wire.

Question 15

What does the strength of the magnetic field produced depend on?

Answer 15

-the distance from the magnet
-the current flowing through the wire 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 16

Describe the magnetic field created when a current flows through a conducting wire? How can you see this?

Answer 16

The field is made up of concentric circles perpendicular to the wire, with the wire in the centre. You can see this by placing a compass near a wire that is carrying a current. As you move the compass, it will trace the direction of the magnetic field.

Question 17

What does changing the direction of the current do to the magnetic field?

Answer 17

it changes the direction of the magnet field

Question 18

What is a solenoid?

Answer 18

a coil of wire?

Question 19

How do you get a solenoid?

Answer 19

increasing the strength of the magnetic field that a wire produces by wrapping the wire into a coil

Question 20

Describe the magnetic field inside and outside the solenoid.

Answer 20

inside a solenoid = strong and uniform - it has the same strength and direction at every point in that region
outside a solenoid = the magnetic field is just like the one round a bar magnet

Question 21

How can you increase the field strength of the solenoid?

Answer 21

by putting a block of iron in the centre of the coil. This iron core becomes an induced magnet whenever current is flowing

Question 22

What happens when you stop the current of a solenoid?

Answer 22

the magnetic field disappears.

Question 23

What is an electromagnet?

Answer 23

a solenoid with an iron core ( a magnet whose magnetic field can be turned on and off with an electric current )

Question 24

Why are electromagnets usually used?

Answer 24

They’re usually used because they’re so quick to turn on and off or because they can create a varying force (like in a loudspeakers)

Question 25

Where are electromagnets used?

Answer 25

-in some cranes to attract and pick up things made from magnetic materials. Using an electromagnet means the magnet can be switched on when you want to pick stuff up, then switched off when you wat to drop it. -Within other circuits to act as switches(e.g in the electric starters of motors) like: -when the switch in a circuit is closed, which attracts the iron contact on the rocker. -the rocker pivots and closes the contacts, completing circuit two and turning on the motor.

Question 26

How can you increase the strength of an electromagnet?

Answer 26

1)increase the current that flows through the solenoid 2)increase the number of coils 3)decrease the length of coil (whilst keeping the number of turns the same) 4)add an iron core

Question 27

What is the motor effect?

Answer 27

When a current carrying wire (or any other conductors) 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 conductor to exert a force on each other. This can cause the wire to move.

Question 28

What direction must the wire be in to experience or not experience a force?

Answer 28

To experience the full force, the wire has to be 90 degrees to the magnetic field. If the wire runs parallel to the magnetic field, it won't experience any force at all. At angles in between it will experience some force.

Question 29

What happens when the strength of the magnetic field increases?

Answer 29

When the strength of the magnetic field increases the magnitude (strength) of the force increases. The force also increases with the amount of current passing through the conductor.

Question 30

What does the force acting on a conductor in a magnetic field depend on?

Answer 30

1)the magnetic flux density - how many field (flux) lines there are in the region 2)the size of the current through the conductor 3)the length of the conductor that's in the magnetic field

Question 31

What does Fleming's left hand rule show?

Answer 31

that if either the current or the magnetic field is reversed, then the direction of the force will also be reversed.

Question 32

What are the units for the formula force =magnetic flux density x current x length

Answer 32

force =magnetic flux density x current x length (N) (T,Tesla) (A) (m)

Question 33

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

Answer 33

Forces act on the two side arms of wire that's carrying a current. These forces are just the usual forces which act on any current in a magnetic field. Because the coil is on a spindle and the forces act one up one down, it rotates. The split ring commutator is a way of swapping the contacts every half turn to keep the motor rotating in the same direction. The direction of the motor can be reversed by reversing the current or by reversing the field (swapping the magnetic poles).

Question 34

How does loudspeakers and headphones use the motor effect?

Answer 34

Loudspeakers and headphones use the motor effect to convert variations in current in electrical circuits to the pressure variations in sound waves.

Question 35

How do loudspeakers and headphones use electromagnets?

Answer 35

An alternating current is sent through a coil of wire attached to the base of a paper cone. The coil surrounds one pole of permanent magnet, and is surrounded by the other pole, so the current causes a force on the coil, which causes the cone to move. When the current reverses, the force acts in the opposite direction, which causes the cone to move in the opposite direction too. So variations in the current make the cone vibrate, which makes the air around the cone vibrate and creates the variations in pressure that causes a sound wave.

Question 36

How can you alter the sound wave produced?

Answer 36

The frequency of the sound wave is the same as the frequency of the alternating current, so by controlling the frequency of the alternating current you can alter the sound waves produced.

Question 37

What is the generator effect?

Answer 37

the induction of a potential difference (and current if there's a complete circuit) in a wire which is moving relative to a magnetic field, or experiencing a change in magnetic field.

Question 38

What does the generator effect create? how can you do this?

Answer 38

a potential difference in a conductor and a current if the conductor is part of a complete circuit. you can do this by moving a magnet in a coil of wire or moving a conductor (wire) in a magnetic field ("cutting" magnetic field lines)