Paper 2 - Topic 7, Magnetism And Electromagnetism

Question 1

What is an alternator

Answer 1

A device that makes use of the generator effect to generate alternating current

Question 2

Define attraction

Answer 2

Opposite poles will experience a force of attraction, meaning they will experience a force towards each other, the force between a magnet and magnetic material and is always one of attraction

Question 3

What happens when a current flows through a wire

Answer 3

A magnetic field is induced around it

Question 4

What is a dynamo

Answer 4

A device that makes use of the generator effect to generate a direct current

Question 5

What is an electric motor

Answer 5

A current carrying coil of wire in a magnetic field, the two sides of the coil that are perpendicular to the magnetic field experience forces in opposite directions causing rotations

Question 6

What is an electromagnet

Answer 6

A solenoid with an iron core

Question 7

What is Flemings Left hand rule

Answer 7

Force = thumb
Current = middle finger
Magnetic field = pointer finger

Question 8

What is the generator effect

Answer 8

When there is a relative motion between an electrical conductor and a magnetic field, a potential difference will be induced across the ends of the conductor, a current will flow if this conductor is part of a complete circuit

Question 9

What is an induced magnet

Answer 9

A material that becomes a magnet when it is placed in an existing magnetic field but loses its magnetism quickly once it is removed, always produce attractive forces

Question 10

What are magnetic field lines

Answer 10

Lines representing the strength and direction of a magnetic field, the field line direction at any point is in the direction that a force would act on another North Pole if placed at that point

Question 11

What is a magnetic field

Answer 11

The region around a magnet in which another magnet or magnetic material will experience a force

Question 12

Give examples of magnetic materials

Answer 12

Iron, steel, cobalt and nickel

Question 13

Describe a microphone

Answer 13

A device that uses the generator effect to convert the pressure variations of sound waves into variations in the electrical current of a circuit

Question 14

What is the motor effect

Answer 14

When a current carrying wire is placed in a magnetic field, a force will be experienced between the wire and the magnet responsible for the field

Question 15

What is a permanent magnet

Answer 15

A magnet that produces its own magnetic field

Question 16

What is repulsion

Answer 16

Like-poles will experience a force of repulsion, meaning they will experience forces in opposite directions

Question 17

What is a solenoid

Answer 17

A wire wrapped into the shape of a coil that has a strong and uniform magnetic field inside

Question 18

What is a step down transformer

Answer 18

A transformer that has a smaller potential difference in the secondary coil than in the primary core

Question 19

What is a step up transformer

Answer 19

A transformer that has a larger potential difference in the secondary coil than in the primary core

Question 20

What is the unit for magnetic flux density

Answer 20

Tesla

Question 21

What is a transformer

Answer 21

An iron core with a primary and secondary coil of wire wound around opposite ends

Question 22

What are the uses of magnetic fields

Answer 22

• generating electricity= rotating a coil of wire through a magnetic field generates a current
• compass = points in the direction of Earths magnetic north and shows the earths core is magnetic

Question 23

If something is 100% efficient what does that mean

Answer 23

Input power = output power

Question 24

What is induced potential

Answer 24

If a conductor or field move relative to each other, a potential is induced across the conductor

Question 25

Which way do field lines point

Answer 25

From north to south

Question 26

How do you increase the strength of a magnetic field

Answer 26

Use a greater current

Question 27

How do you create a weaker field

Answer 27

Greater distance from the wire

Question 28

How do you increase the strength of a solenoid

Answer 28

Have an iron core in the centre as it is easier for magnetic field lines to pass through than air

Question 29

What factors affect the strength of a solenoid

Answer 29

- size of the current - length - cross sectional area - number of turns in the coil - using a soft iron core

Question 30

What happens when their is relative movement between a conductor and a magnetic field

Answer 30

A potential difference is induced across the conductor

Question 31

How do dynamic microphones work

Answer 31

- they produce a current which is proportional to the sound signal - fixed magnet is at the centre and the coil of wire around the magnet is free to move - pressure variations in the sound waves cause the coil to move and as it moves current is induced in the coil - the current is then sent to a loudspeaker

Question 32

How do loudspeakers work

Answer 32

- current flows into coil - the magnetic field from magnet and from current interaction causing the coil to move - the cone therefore moves - producing pressure variations making sound

Question 33

What does a magnetic compass contain

Answer 33

A small bar magnet that points in the direction of the Earths magnetic field

Question 34

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

Answer 34

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

Question 35

If the direction of current in a current-carting site placed in a uniform magnetic field is reversed, what happens to the force

Answer 35

The direction of the force is reveresed

Question 36

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

Answer 36

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

Question 37

How is the pitch of the sound from a loudspeaker changed

Answer 37

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

Question 38

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

Answer 38

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

Question 39

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

Answer 39

- 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 40

Describe the makeup of a basic transformer

Answer 40

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

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