Electromagnetism

Question 1

How would you plot magnetic field lines using a plotting compass?

Answer 1

You’d move the compass gradually around the edges of the bar magnet and makes marks in the places where the arrow of the compass points, then plot all the points together

Question 2

Give four examples of magnetic materials.

Answer 2

Iron
Steel
Nickel
Cobalt

Question 3

What rule is used to know which way the magnetic field travels around a current carrying wire?

Answer 3

Right hand thumb rule

Question 4

Which way does a magnetic field travel in a bar magnet?

Answer 4

North to south

Question 5

What is a permanent magnet?

Answer 5

A magnet that produces its own magnetic field

Question 6

What is an induced magnet?

Answer 6

A magnetic material that becomes a magnet when put into a magnetic field

Question 7

What two things make the magnetic field around a current carrying wire stronger?

Answer 7

A shorter distance from the wire

A higher current carried

Question 8

What is an electromagnet?

Answer 8

A magnet whose magnetic field can be switched on or off using an electric current

Question 9

What is a solenoid?

Answer 9

A coil of wire

Question 10

Why does having more coils in an electromagnet make it stronger?

Answer 10

The field lines around each loop line up with each other so there will be lots of them, all close together

Question 11

Give one example of a use of an electromagnet.

Answer 11

Cranes

Switches in circuits

Question 12

What is the motor effect?

Answer 12

The act of movement being created by a current carrying wire being placed in between two magnets

Question 13

True or false?

For the motor effect, the wire should be at 90 degrees to a magnetic field to experience full force

Answer 13

True

Question 14

What will happen in the motor effect if the wire runs parallel to the magnetic field?

Answer 14

There will be no force/movement at all

Question 15

What is magnetic flux density?

Answer 15

The amount of field lines that there are in a region

i.e. The strength of the magnet

Question 16

How do you find the direction of the force which has the motor effect?

Answer 16

Fleming’s left hand rule

Question 17

How does Fleming’s left hand rule work?

Answer 17

1. Point your first finger in the direction of the field
2. Point your second finger in the direction of the current
3. Your thumb will then point in the direction of the force

Question 18

How do electric motors use the motor effect?

Answer 18

The current carrying wire between the two magnets cause a force to be exerted, and (use Fleming’s left hand rule) one will be up and one will be down meaning the movement created is a rotation

Question 19

How does a motor continue to spin using the motor effect rather than swap back and forth?

Answer 19

It has a split ring commutator to swap the direction of the current every half turn and therefore swap the direction of the forces.

Question 20

Define the term generator effect.

Answer 20

The induction of a potential difference (and current if there’s a complete circuit) in a wire which is experiencing a change in magnetic field

Question 21

True or false?

The force between a permanent magnet and an induced magnet is always attractive

Answer 21

True

Question 22

Give some ways on how you might increase the strength of a solenoid.

Answer 22

More coils
Increase the tightness of the coils
Add an iron core
Increase the current

Question 23

True or false?

In the motor effect, the strength of the force increases with the strength of the magnetic field and the amount of current passing through the conductor.

Answer 23

True

Question 24

True or false?

The force between a permanent magnet and an induced magnet is always attractive.

Answer 24

True

Question 25

What is the magnetic field like inside a solenoid?

Answer 25

Strong and uniform | It has the same strength and direction at every point in that region

Question 26

True or false? In the motor effect, the magnitude (strength) of the force decreases with both the strength of the magnetic field and the amount of current passing through the conductor.

Answer 26

False | It increases

Question 27

What kinds of 'change in magnetic field' would be experienced in the generator effect?

Answer 27

A magnet is moved into a coil of wire The wire is moved A magnet is rotated The wire is rotated

Question 28

Why is a potential difference induced in the generator effect?

Answer 28

Because the wire experiences a force which transfers energy

Question 29

How can a potential difference induce an alternating current?

Answer 29

A continuous movement backwards and forwards of the magnet or coil cause the potential difference to keep changing direction so induces the alternating current

Question 30

True or false? In the generator effect, an induced current always opposes the change that made it.

Answer 30

True

Question 31

Give two ways to increase the size of an induced potential difference?

Answer 31

Increase the speed of the movement | Increase the strength of the magnetic field

Question 32

What is the difference between an alternator and a dynamo?

Answer 32

Alternators generate alternating current | Dynamos generate direct current

Question 33

What would use an oscilloscope for relating to the generator effect?

Answer 33

To see the generated potential difference

Question 34

What would an oscilloscope trace for an alternating potential difference?

Answer 34

A sinusoidal curve

Question 35

Would an oscilloscope trace for a direct potential difference?

Answer 35

Repetitive 'hills' (curved lines) | Never crosses 0

Question 36

Do loudspeakers use the generator effect or the motor effect?

Answer 36

Motor effect

Question 37

Describe how a loudspeaker works.

Answer 37

- An alternating current is sent through a coil of wire attached to the base of a paper cone - The coil surrounds one pole of a permanent magnet while it's surrounded by the other pole meaning the current causes a force on the coil (so the cone moves) - When the current alternates, the movement occurs in the opposite direction because the force does too - This causes the cone to vibrate and therefore the air to vibrate and create variations in pressure which create a soundwave

Question 38

How could you alter a sound wave produced by a loudspeaker?

Answer 38

Change the frequency of the alternating current as this will also change the frequency of the sound wave

Question 39

Do microphones use the generator effect or the motor effect?

Answer 39

Generator effect

Question 40

Describe how a microphone works.

Answer 40

- Sound waves hit a flexible diaphragm that is attached to a coil of wire, wrapped around a magnet - The sound wave causes the coil of wire to move into the magnetic field and so generates a current

Question 41

True or false? In microphones, the movement of the coil depends on the properties of the sound wave.

Answer 41

True

Question 42

Do transformers use the generator effect or the motor effect?

Answer 42

Generator effect

Question 43

True or false? Transformers only work with a direct current.

Answer 43

False | They only work with an alternating current

Question 44

What do transformers do?

Answer 44

Change the size of the potential difference of an alternating current

Question 45

What happens in a transformer if an alternating current is applied across the primary coil?

Answer 45

The iron core magnetises and demagnetises quickly and the changing magnetic field therefore induces an alternating potential difference in the secondary coil If the secondary coil is part of a complete circuit, a current is induced too

Question 46

What's the difference between step-up transformers and step-down transformers?

Answer 46

Step-up transformers increase the potential difference - they have more turns on the secondary coil Step-down transformers decrease the potential difference - they have more turns on the primary coil

Question 47

Why is energy carried at a high potential difference through the national grid?

Answer 47

So the current is low, which reduces energy wasted to surroundings