Magnetism and electromagnetism

Question 1

At which part of a magnet are the magnetic forces strongest?

Answer 1

At the poles of the magnet

Question 2

What happens when two magnets are brought close to each other?

Answer 2

They exert a force on each other

Question 3

What type of force is exerted if two like poles of a magnet are brought near each other

Answer 3

A repulsive, non contact force

Question 4

What type of force is exerted if two unlike poles of a magnet are brought near each other

Answer 4

An attractive, non contact force

Question 5

What is the difference between a permanent magnet and an induced magnet?

Answer 5

• Permanent magnet produces its own magnetic field
• An induced magnet becomes magnetic when placed in a magnetic field

Question 6

What type of force does induced magnetism always cause?

Answer 6

Force of attraction

Question 7

What happens when an induced magnet is removed from a magnetic field?

Answer 7

the induced magnet loses all its magnetism

Question 8

What is a magnetic field?

Answer 8

The region surrounding a magnet where another magnet or magnetic material experiences a non contact force

Question 9

Give four examples of magnetic materials

Answer 9

Iron
Cobalt
Steel
Nickel

Question 10

What can always be said about the force between a magnet and a magnetic field?

Answer 10

It is always an attractive force

Question 11

How does the strength of a magnetic field alter as you move further away from the magnet producing it

Answer 11

Magnetic field strength decreases as you move further away

Question 12

In what direction does a magnetic field point?

Answer 12

• In the direction that a north pole would experience a force if placed in the field
• Form the north seeking pole to the south seeking pole of a magnet

Question 13

What does a magnet compass contain?

Answer 13

A tiny bar magnet
Points in direction of Earth’s magnetic field
Always point towards the south pole of a magnet

Question 14

What is produced when current flows through a conducting wire?

Answer 14

A magnetic field is produced around the wire

Question 15

What determines the strength of the magnetic field around a current-carrying wire?

Answer 15

• Magnitude of the current flowing through the wire
• Distance from the wire

Question 16

What is a solenoid?

Answer 16

Coil of wire which when current passes through creates a strong magnetic field

Question 17

Describe the magnetic field found inside a solenoid

Answer 17

Strong and uniform

Question 18

What is an electromagnet

Answer 18

• Solenoid with an iron core
• iron core increases strength of magnetic field

Question 19

What is the motor effect

Answer 19

When a force is exerted between a magnetic field and a current-carrying wire placed in that field

Question 20

What rule is used to determine the force experienced due to the motor effect?

Answer 20

Fleming’s left hand rule

Question 21

When using Fleming’s left hand rule, what do the fingers represent?

Answer 21

Thumb - Direction of the force, which results in the motion
Forefinger - Direction of magnetic field
Middle finger - Direction of current flow in the conductor

Question 22

What factors affect the size of the force on a current carrying wire in a magnetic field?

Answer 22

• Magnitude of current
• Strength of magnetic field

Question 23

What happens to force on a current carrying wire when current is reversed?

Answer 23

• Direction of the force is reversed

Question 24

What criteria must be met for the equation linking force, magnetic flux density, current and length to hold?

Answer 24

• The conductor must be at right-angles to the magnetic field it is placed in

Question 25

Unit for magnetic flux density

Answer 25

Tesla (T)

Question 26

How does an electric motor work?

Answer 26

- Coil of wire, carrying a current is placed in a magnetic field - The forces on the two sides perpendicular to the field experience forces in opposite directions - Causing a rotational effect

Question 27

How do loudspeakers make use of motor effect?

Answer 27

- Used to convert variations in the current of an electrical circuit into the pressure variations which produce audible sound

Question 28

Explain how a loudspeaker works

Answer 28

- A cone with a wire wrapped around it is connected to an a.c power supply and is placed in a permanent magnetic field - When current flows through the wire, it creates a second magnetic field which interacts with the permanent field - This produces a force which causes the cone to vibrate

Question 29

How is the pitch of a sound from a loudspeaker changed

Answer 29

- Frequency of the a.c current is altered - This creates a different frequency of vibration in a cone

Question 30

What happens when an electrical conductor moves relative to a magnetic field?

Answer 30

A potential difference is induced across the ends of the conductor

Question 31

What happens to an electrical conductor when there is a change to the magnetic field that it is placed in

Answer 31

A potential difference is induced across the ends of the conductor

Question 32

What is the requirement for an induced potential difference to cause a current flow?

Answer 32

The conductor must form a closed loop or be part of a complete circuit

Question 33

What can be said about the direction of the magnetic field produced by an induced current?

Answer 33

- The direction of the field is such that it opposes the change that induced the current - This change is either the movement of the conductor or a change to the field

Question 34

What are two ways that the generator effect is used to generate different types of current?

Answer 34

- In an alternator to produce alternating current - In a dynamo to produce a direct current

Question 35

What electromagnetic effect does a microphone take advantage of and how?

Answer 35

- The generator effect - Converts the pressure variations in sound waves into alternating current in a circuit

Question 36

Describe the makeup of a basic transformer

Answer 36

A primary coil and a secondary coil of wire wrapped around an iron core

Question 37

Why is iron used as the core for a transformer?

Answer 37

It is easily magnetised

Question 38

Explain how a transformer works

Answer 38

- Alternating current flows through the primary coil - This induces a changing magnetic field in the core - This changing magnetic field induces a current to flow in the secondary coil

Question 39

Why must the current flowing through the primary coil of a transformer be alternating?

Answer 39

- For current to be induced in the secondary coil, the magnetic field in the core must be continuously changing - For the magnetic field to be changing, the current in the primary coil must be alternating