Electromagnetism

Question 1

What is a permanent magnet?

Answer 1

A magnet that is always magnetised and produces its own magnetic field

Question 2

What is an induced magnet?

Answer 2

A magnet that only has a magnetic field when induced by another magnet

Question 3

Examples of magnetic materials

Answer 3

Iron, cobalt, steel, nickel

Question 4

What is the force between like poles?

Answer 4

Repel

Question 5

What is the force between unlike poles?

Answer 5

Attracts

Question 6

What happens to field strength as distance decreases?

Answer 6

It increases

Question 7

What type of magnet is the Earth?

Answer 7

A permanent magnet

Question 8

How do we know the Earth is a permanent magnet?

Answer 8

A compass will always point to the North pole

Question 9

How do you show magnetic field lines?

Answer 9

Iron filings or plotting compasses

Question 10

What is the right hand thumb rule?

Answer 10

The direction of your fingers is the direction of the field and the direction of your thumb is the direction of the current

Question 11

What is a solenoid?

Answer 11

A coil of current-carrying wire

Question 12

How can the strength of a magnetic field of a solenoid be increased?

Answer 12

Increase current, more turns of wire, placing turns closer together, putting a soft iron core into the middle of a solenoid

Question 13

What are uses of electromagnets?

Answer 13

Scrapyards, school gates, speakers, microphones, doorbells

Question 14

What is the motor effect?

Answer 14

If a current carrying wire is placed in a magnetic field the wire will move

Question 15

What does Flemings left hand rule show us?

Answer 15

Thumb - Motion/force
Fore finger - Magnetic field
Second finger - Current

All should be at a right angle to each other

Question 16

What is the equation for force?

Answer 16

Force = magnetic flux density x current x length

Question 17

How many amps is in a milliamp?

Answer 17

1000 amps

Question 18

Which way does the magnetic field act?

Answer 18

From North to South

Question 19

What is a DC a motor?

Answer 19

A coil or wire in a magnetic field

Question 20

How does a DC motor work?

Answer 20

1. When a current flows through the coil, a magnetic field is created
2. This magnetic field interacts with the magnetic field from the motor and creates a force
3. There’s an equal and opposite force on each side of the coil because the current on each side of the coil is flowing in opposite directions
4. This force causes the motor to rotate
5. When the coil has rotated 180 degrees, the current is now flowing in the opposite direction to before
6. This means that the coil would experience a force in the opposite direction
7. To prevent this a split ring commutator changes the direction of every half turn due to two halves of the coil swapping from one carbon brush to another
8. This allows for the motor to experience a force in the same direction at any position within the field of the permanent magnet
9. The commutator disconnects the current every half turn but momentum keeps the motor rotating

Question 21

How does an AC motor work?

Answer 21

1. When a current flows through the coil, a magnetic field is created
2. This magnetic field interacts with the magnetic field from the motor and creates a force
3. There’s an equal and opposite force on each side of the coil because the current on each side of the coil is flowing in opposite directions
4. This force causes the motor to rotate
5. When the coil has rotated 180 degrees, the current is now flowing in the opposite direction to before
6. This means that the coil would experience a force in the opposite direction

Question 22

What is the difference between an AC and DC motor?

Answer 22

An AC motor doesn’t need a commutator because the current is alternating but a DC motor does

Question 23

What can you do to make the motor spin in the direction?

Answer 23

Reverse direction of current or reverse direction of magnetic field

Question 24

What can you do to make the motor faster?

Answer 24

Increase the current, increase the magnetic flux density, increase the number of turns in the coil

Question 25

How can you induce potential difference?

Answer 25

Moving a coil of wire into a magnetic field or moving a magnet into a coil of wire

Question 26

What is the generator effect?

Answer 26

The motion of a wire in a magnetic field induces current

Question 27

What happens when a magnet is stationary?

Answer 27

No current is induced

Question 28

How can you increase the induced current using the generator effect?

Answer 28

Faster movement, stronger magnetic field, more turns in the coil, larger area of coils

Question 29

What is a dynamo?

Answer 29

A DC generator

Question 30

How does a Dynamo work?

Answer 30

The coil is spun making it experience a changing magnetic field which induces potential difference. If the coil is in a complete circuit then a current is induced

Question 31

What is the commutator used in a dynamo called?

Answer 31

Slip ring commutator

Question 32

What happens when a magnet moves in the opposite direction?

Answer 32

Current is increased in the opposite direction

Question 33

Why do dynamos use slip ring commutators?

Answer 33

To make DC from AC

Question 34

What is an alternator?

Answer 34

An AC generator

Question 35

What happens if the dynamo is rotated twice?

Answer 35

The frequency would double

Question 36

How potential difference induced from dynamos?

Answer 36

When the coil moves in a directions where it’s cutting through the magnetic field lines, PD is the greatest As the coil continues to rotate PD decreases When the coil moves in the same directions as the magnetic field lines no PD is induced As the coil continues to rotate PD increases Until it reaches a maximum when it moves through horizontal, cutting through magnetic field lines again

Question 37

How does an alternator work?

Answer 37

A rectangular coil is made to spin in a uniform magnetic field, causing an alternating current to be induced in the coil

Question 38

How does an electric motor work?

Answer 38

The force in a current carrying wire in a magnetic field pushes one side of the coil down and the other side up

Question 39

What does a changing magnetic field around a conductor produce?

Answer 39

A potential difference that can create a current

Question 40

What does a loudspeaker consist of?

Answer 40

A coil that vibrates when AC flows through it

Question 41

How does a loudspeaker work?

Answer 41

1. The current creates a magnetic field 2. This magnetic field interacts with the permanent magnet in the loudspeaker, causing a force 3. As the current changes direction, this then vibrates a cone 4. The vibrating cone causes pressure variations in the air and forms longitudinal sound waves

Question 42

How does a microphone work?

Answer 42

1. The sound waves cause a flexible diaphragm to vibrate 2. The vibration causes a coil to move around a permanent magnet 3. This changing magnetic field around the coil induced a potential difference 4. Because the coil is in a complete circuit, this then induces a current 5. This current in the electrical output from the microphone

Question 43

What do loudspeakers do?

Answer 43

Turns electrical signals into sound waves

Question 44

What do microphones do?

Answer 44

Turn sound waves into electrical signals