P4 - Magnetism and Magnetic Fields

Question 1

Give the three magnetic materials

Answer 1

Iron,nickel and cobalt

Question 2

In which direction do magnetic field lines always point?

Answer 2

North to South

Question 3

What does the distance between field lines tell you about a magnetic field?

Answer 3

The closer the lines are together, the stronger the magnetic field

Question 4

What is the magnetic flux density and what unit is it measured in?

Answer 4

Magnetic Flux Density - strength of the magnetic field

Measured in Tesla’s (T)

Question 5

What is the difference between a permanent and induced magnet?

Answer 5

Permanent - Metals that have magnetic domains which line up even when not in an magnetic field ( they are permanently magnetic)

Induced - Have domains which line up only exposed to a magnetic field

Question 6

Describe what happens to magnetic field strength as you get further from a current-carrying wire

Answer 6

The field strength will decrease

Question 7

Why could a magnet and a current -carrying wire conductor feel a force when they’re near each other?

Answer 7

If the wires magnetic field is in the opposite to the magnets field the wire will experience a force

Question 8

At what angle must a current-carrying wire be to an external magnetic field to feel the maximum force?

Answer 8

90 degrees

Question 9

Describe what is/ how to use Flemings left hand rule

Answer 9

It is a way to find the direction of the force on a current-carrying wire in a magnetic field

Thumb = Force
First Finger= Magnetic field
Second finger= Direction of current

Question 10

What’s the equation to find the force on a conductor carrying a current?

Answer 10

Force on a conductor carrying a current(N) = magnetic flux density (T) x current (I) x length (m)

Question 11

Explain how magnetic forces are used in

a) electric motor
b) loudspeakers

Answer 11

a) In a motor, a current-carrying coil sits between two opposite poles of a magnet. As there is a current and a magnetic field the wire will experience a force
b) Similarly, a current is fed into a cool which is between two magnets. It will experience a force which moves the coil in and out, creating sound out of the diaphragm

Question 12

What is electromagnetic induction?

Answer 12

If you you use a conductor to cut the magnetic field lines between two magnets, it induces a voltage through the conductor (wire).

Question 13

What type of current does a alternator produce?

Answer 13

a.c (OBVIOUSLY)

Question 14

What would happen to the current produced by a dynamo if the direction of rotation of the coil was reversed?

Answer 14

It would be reversed

Question 15

Explain how a dynamic microphone converts sound waves to electrical signals

Answer 15

Sound wave hit the diaphragm of a microphone causing it to move in and out. This then produces kinetic energy and a voltage which is transferred to electrical signals

Question 16

What type of current is required for a transformer to work?

Answer 16

Alternator current (a.c)

Question 17

Explain how a transformer works?

Answer 17

When an alternating p.d is applied across the primary coil, it produces an alternating magnetic field. The iron core becomes magnetised and induced a p.d in the secondary coil. Depending on the amount of turns in the secondary coil, the p.d will either increase your decreases

Question 18

What’s the difference between a step-up and step-down transformer?

Answer 18

Step up increases the p.d - has more turns in secondary than primary

Step down decreases the p.d - has more turns in primary coil

Question 19

What is the equation to calculate the p.d or no. of turns in a transformer?

Answer 19

Primary coil p.d divided by secondary coil p.d = Numbers of turns in primary divided by number of turns in secondary