Electromagnets

Question 1

Which metals are magnetic?

Answer 1

• Iron
• Cobalt
• Nickel
• Steel

Question 2

Which direction do magnetic field lined flow in?

Answer 2

From north to south.

Question 3

What is a permanent magnet?

Answer 3

A material that produces its own magnetic field.

Question 4

What is an induced magnet?

Answer 4

A material that becomes a magnet when placed in a magnetic field.

Question 5

What causes the Earth’s magnetic field?

Answer 5

The molten iron outer core.

Question 6

Why do compasses point to the north pole?

Answer 6

It is the magnetic south pole.

Question 7

What is a magnetic field?

Answer 7

The area around a magnet where a force will be exerted on another magnet/magnetic material.

Question 8

Which end is the south pole of a solenoid?

Answer 8

The end where the current flows clockwise.

Question 9

Which end is the north pole of a solenoid?

Answer 9

The end where the current flows anti-clockwise.

Question 10

How can the strength of a solenoid by increased?

Answer 10

• Increasing the number of turns
• Increasing the current
• Adding an iron core

Question 11

What is Fleming’s left hand rule?

Answer 11

Thumb: Motion
First finger: Magnetic field
Second finger: Current

Question 12

How can the force on a wire in a magnetic field be increased?

Answer 12

• Increasing the current
• Increasing the magnetic flux density
• Increasing the length of wire in the magnetic field

Question 13

What happens if current flows through a wire in the same direction as the magnetic field?

Answer 13

The force on the wire is 0N

Question 14

What is the motor effect?

Answer 14

Force acting on a wire placed in a magnetic field when current flows through it.

Question 15

Why is a split ring commutator used in a DC motor?

Answer 15

It reverses the direction of the current every half turn so the coil experiences a force in the same direction, despite each side cutting through the magnetic field line in the opposite direction.

Question 16

Why does the motor continue spinning even though the brushes disconnect every half turn?

Answer 16

Its momentum keeps it spinning until the brushes reconnect.

Question 17

Why does the coil of a motor spin?

Answer 17

• The current in the coil creates a magnetic field
• This interacts with the permanent magnet
• The current flows in opposite directions on the two sides of the coil
• The forces act in opposite directions, making it spin.

Question 18

How does a loudspeaker work?

Answer 18

• AC current in coil reverses poles of solinoid
• Interaction between magnetic fields causes vibrations in the cone
• This moves air molecules, creating the pressure variations needed for sound waves.

Question 19

What is electromagnetic induction?

Answer 19

Potential difference induced in a conductor when it cuts through magnetic field lines, causing current to flow.

Question 20

Why do you have to do work when moving a magnet through a coil of wire?

Answer 20

• The polarity of the solenoid will change to oppose the movement
• Energy used is transferred along the coil of wire

Question 21

When moving a bar magnet in a coil of wire to induce a potential difference, how do you create a higher potential difference?

Answer 21

Moving the magnet faster.

Question 22

What is an alternator?

Answer 22

An AC generator.

Question 23

How can an induced current be increased?

Answer 23

• Increasing the speed of the coils rotation
• Increasing the strength of the magnetic field
• Increasing the number of turns in the coil
• Increasing the total area of the coil

Question 24

What is a dynamo?

Answer 24

A DC generator.

Question 25

Why are slip rings and brushes used in an AC generator?

Answer 25

- They ensure that the wires do not get tangled - The brushes are an electrical contact

Question 26

What happens if a DC generator is rotated twice as fast?

Answer 26

- The frequency is doubled - The amplitude is doubled

Question 27

Why are electromagnets used instead of permanent magnets for a scrapyard crane?

Answer 27

They can be turned off to drop objects.

Question 28

How does a circuit breaker work?

Answer 28

- Push switch is held in place iron bolt - Electromagnet is put into the circuit next to the bolt - When the current gets too high, the magnet pulls out the bolt

Question 29

How does an electric bell work?

Answer 29

- Electromagnet attracts metal arm - Arm hits the gong and breaks the circuit connection - This switches off the electromagnet - Arm moves back - The circuit is completed again

Question 30

What is a relay switch?

Answer 30

- An electromagnetic switch - Allows a small circuit to turn on/off a much larger circuit.

Question 31

What are the 2 ways a relay switch can be used?

Answer 31

- A switch - An amplifyer

Question 32

How does a relay switch work?

Answer 32

- It has a coil of wire which becomes a temporary magnet - This attracts a switch for a larger circuit, turning it on/off

Question 33

How does a microphone work?

Answer 33

- Sound waves move diaphragm - Diaphragm moves a coil, making it cut through magnetic field lines - This induces a potential difference in the coil - Electrical signal matches the sound waves

Question 34

How does a transformer work?

Answer 34

- AC in primary coil induces a changing magnetic field in the core - Secondary coil cuts through changing fie;d lines, so alternating potential difference is induced - Number of turns on each side determines the voltage output

Question 35

What does a step up transformer do?

Answer 35

Increases voltage and decreases current.

Question 36

What does a step down transformer do?

Answer 36

Decreases voltage and increases current.

Question 37

Which side is the primary coil on a step up transformer?

Answer 37

The coil with less turns on it.

Question 38

Which side is the primary coil on a step down transformer?

Answer 38

The coil with more tuns on it.

Question 39

What are the 2 uses of transformers?

Answer 39

- Increasing efficiency in power transmission - Changing mains voltage for different devices

Question 40

What are transformer cores made from?

Answer 40

Iron.