P15 - Electromagnetism

Question 1

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

Answer 1

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

● A 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

A force of attraction.

Question 7

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

Answer 7

The induced magnet loses most/all of 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

1. Iron
2. Steel
3. Cobalt
4. Nickel

Question 10

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

Answer 10

It is always attractive.

Question 11

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

Answer 11

The magnetic field strength decreases the further you move 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
● From the north seeking pole to the south seeking pole of a magnet

Question 13

What does a magnetic compass contain?

Answer 13

A small bar magnet that points in the direction of the Earth’s magnetic field.

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

● The magnitude of the current flowing through the wire
● The distance from the wire

Question 16

What is a solenoid?

Answer 16

A 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

● A solenoid with an added iron core
● Adding the iron core increases the strength of the magnetic field

Question 19

What is the motor effect?

Answer 19

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

Question 20

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

Answer 20

Fleming’s Left-Hand Rule

Question 21

When using Fleming’s left hand rule what does the forefinger represent?

Answer 21

The forefinger points in the direction of the magnetic field.

Question 22

When using Fleming’s left hand rule what does the second finger represent?

Answer 22

The second finger points in the direction of current flow in the conductor.

Question 23

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

Answer 23

● The magnitude of the current flowing through the conductor
● The strength of the magnetic field that the conductor is placed in

Question 24

If the direction of current in a current-carrying wire placed in a uniform magnetic field is reversed, what happens to the force?

Answer 24

The direction of the force is reversed.

Question 25

If the strength of the current in a current-carrying wire placed in a uniform magnetic field is increased, what happens to the force?

Answer 25

The strength of the force is increased.

Question 26

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

Answer 26

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

Question 27

What is the unit used for magnetic flux density?

Answer 27

Tesla, T

Question 28

How does an electric motor work?

Answer 28

● A 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 ● This causes a rotational effect

Question 29

How do loudspeakers make use of the motor effect?

Answer 29

The motor effect is used to convert variations in the current of an electrical circuit into the pressure variations which produce audible sound.

Question 30

Explain how a loudspeaker works.

Answer 30

● 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 31

How is the pitch of the sound from a loudspeaker changed?

Answer 31

● The frequency of the a.c current is altered ● This creates a different frequency of vibration in the cone

Question 32

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

Answer 32

A potential difference is induced across the ends of the conductor.

Question 33

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

Answer 33

A potential difference is induced across the ends of the conductor.

Question 34

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

Answer 34

A potential difference is induced across the ends of the conductor.

Question 35

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

Answer 35

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

Question 36

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

Answer 36

● 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 37

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

Answer 37

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

Question 38

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

Answer 38

● The generator effect ● It converts the pressure variations in sound waves into alternating current in a circuit

Question 39

Describe the makeup of a basic transformer.

Answer 39

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

Question 40

Why is iron used as the core for a transformer?

Answer 40

It is easily magnetised.

Question 41

Explain how a transformer works.

Answer 41

● An alternating current flows through the primary coil ● This induces a changing magnetic field in the core ● This changing magnetic induces a current to flow in the secondary coil

Question 42

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

Answer 42

● 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

Question 43

What can be said about the electrical power input and output of a 100% efficient transformer?

Answer 43

The electrical power input is equal to the electrical power output.