Separate Physics - P7 Magnetism and Electromagnetism

Question 1

Name the three magnetic materials.

Answer 1

• Iron
• Cobalt
• Nickel

Question 2

What happens when two ‘like’ poles are brought together?

Answer 2

They repel each other

Question 3

Is magnetism an example of a contact or non-contact force?

Answer 3

Non-contact force

Question 4

What do you call a material that becomes magnetic when it is placed in the magnetic field of another magnet?

Answer 4

Induced magnet

Question 5

Draw the magnetic field lines around a bar magnet.

Answer 5

Question 6

What happens when two opposite poles are brought together?

Answer 6

They attract each other

Question 7

Complete the diagram to show the directions that the plotting compasses will point.

Answer 7

Question 8

Draw the magnetic field around an electromagnet.

Answer 8

Question 9

What happens when a current flows through a wire?

Answer 9

A magnetic field is produced

Question 10

Describe the magnetic field lines in the middle of an electromagnet.

Answer 10

Strong and uniform

Question 11

Give three ways in which you can increase the strength of an electromagnet.

Answer 11

• Increase the voltage
• Increase the number of coils on the wire
• Use a soft iron core in the middle

Question 12

Higher Q. In Fleming’s left-hand rule, what do the following represent?

a) First finger
b) Second finger
c) Thumb

Answer 12

a) Field (North to south)
b) Current (positive to negative)
c) Movement

Question 13

What is a coil of wire called?

Answer 13

A Solenoid

Question 14

Give two advantages of an electromagnet over a permanent magnet?

Answer 14

• You can turn an electromagnet on and off.
• You can change the strength of the electromagnet

Question 15

What causes the Earth to have a magnetic field?

Answer 15

Liquid iron in the Earth’s core

Question 16

Higher Q. What is the motor effect?

Answer 16

A conductor carrying a current placed in a magnetic field causes the magnet and the conductor to exert a force on one another.

Question 17

Separate Higher Q. What three things affect the size of the force on a conductor in a magnetic field?

Answer 17

1. The magnetic flux density.
2. The length of the conductor that’s in the magnetic field.
3. The size of the current through the conductor.

Question 18

Separate Higher Q. In a loudspeaker or headphones, how is the frequency of the sound wave determined?

Answer 18

The frequency of the sound wave is the same as the frequency of the AC.

Question 19

Separate Higher Q. What two things could you do to induce a potential difference across the ends of a conductor?

Answer 19

1. Move a magnet in and out of a coil of wire
2. Moving a conducting wire inside a magnetic field

Question 20

Separate Higher Q. What type of current is generated by an alternator?

Answer 20

Alternating current - AC

Question 21

Separate Higher Q. Describe how loudspeakers and headphones work.

Answer 21

• AC current is passed through a coil of wire.
• The coil is wrapped around one pole of a magnet (e.g. South).
• This is placed inside a magnet of the opposing pole (e.g. North).
• A paper cone is attached to the coil of wire.
• As the current alternates, this moves the paper cone out and in.
• As the cone oscillates, this cause vibrations in the air outside the cone and hence a sound wave is produced.

Question 22

Separate Higher Q. What is the generator effect?

Answer 22

• A potential difference induced across the ends of a conductor if the conductor moves relative to a magnetic field.
• If the circuit is complete, a current will be induced.

Question 23

Separate Higher Q. Give two ways that you could increase the size of an induced potential difference/current.

Answer 23

1. Increasing the speed of movement of the conducting wire relative to the magnetic field
2. Increasing the strength of the magnetic field

Question 24

Separate Higher Q. What type of current is generated by a dynamo?

Answer 24

Direct current - DC

Question 25

**Separate Higher Q**. Describe how a microphone works.

Answer 25

* The microphone’s diaphragm is attached to a coil of wire. * The coil of wire is wrapped around a permanent magnet of a particular pole (e.g. south). * This magnet and wire sit inside another magnet of opposing pole (e.g. north). * Sound waves vibrate the diaphragm causing the coil to move in and out. * A current is generated in the wire.

Question 26

**Separate Higher Q**. If a transformer was 100% efficient, what would the electrical power output equal?

Answer 26

The electrical power output would equal the electrical power input

Question 27

**Separate Higher Q**. What’s the relationship between the ratio of the **number of turns** on the primary and secondary coils and ratio of the **potential difference** of the primary and secondary coils?

Answer 27

The ratio of the **number of turns** on the primary and secondary coils _is the same as_ the ratio of the **potential differences** of the primary and secondary coils.

Question 28

**Separate Higher Q**. Do loudspeakers and headphones use the motor effect or the generator effect?

Answer 28

The motor effect

Question 29

**Separate Higher Q**. What does a basic transformer consist of?

Answer 29

A primary and secondary coil wound on an iron core

Question 30

**Separate Higher Q**. Describe how a transformer works.

Answer 30

* An alternating potential difference is applied across the primary coil. * The iron core magnetises then demagnetises due to the AC current. * This change in magnetic field induces a potential difference in the secondary coil. * If the secondary coil is connected to a complete circuit, a current will be induced.

Question 31

**Separate Higher Q**. Describe how an alternator works.

Answer 31

* Coil of wire spins inside a magnetic field. * A current is induced in the coil. * Slip rings and brushes are used so the current remains alternating.

Question 32

**Separate Higher Q**. Do microphones use the motor effect or the generator effect?

Answer 32

The generator effect

Question 33

**Separate Higher Q**. Describe how a dynamo works.

Answer 33

* Coil of wire spins inside a magnetic field. * A current is induced in the wire. * A split ring commutator swaps the connections every half-turn so the current stays in the same direction. * A direct current (DC) is produced.

Question 34

**Separate Higher Q**. Why is iron used as the core of a transformer?

Answer 34

Iron is easily magnetised

Question 35

**Separate Higher Q**. What type of transformer has more coils on the secondary coil than the primary coil?

Answer 35

Step-up transformer

Question 36

**Separate Higher Q**. What type of current are transformers used with?

Answer 36

Alternating Current

Question 37

**Separate Higher Q**. What type of transformer has more coils on the primary coil than the secondary coil?

Answer 37

Step-down transformer

Question 38

**Separate Higher Q**. If the frequency of revolutions of the generator was increased, how would this oscilloscope trace change?

Answer 38

1. More peaks 2. Higher peaks

Question 39

**Separate Higher Q**. What type of current does this oscilloscope trace show?

Answer 39

Direct Current

Question 40

**Separate Higher Q**. What type of current does this oscilloscope trace show?

Answer 40

Alternating current