P15: Magnetism

Question 1

Where are the poles of magnets?

Answer 1

The places where the magnetic forces are strongest

Question 2

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

Answer 2

A permanent produces its own magnetic field whereas an induced is a material that becomes a magnet when it is placed in a magnetic field.

Question 3

What do induced magnets always cause?

Answer 3

A force of attraction

Question 4

What are the 4 magnetic materials?

Answer 4

Iron, steel, cobalt and nickel

Question 5

What is a magnetic field?

Answer 5

The region around a magnet where a force acts on another magnet or another magnetic material

Question 6

What does the strength of a magnetic field always depend on?

Answer 6

The distance from the magnet

Question 7

When is a magnetic field produced around a conducting wire?

Answer 7

When a current flows through it

Question 8

What 2 things does the strength of a magnetic field around a conducting wire depend on?

Answer 8

The current through the wire and the distance from the wire

Question 9

What pole does the field lines come out of a bar magnet?

Answer 9

North

Question 10

What are the 4 ways you can increase an electromagnetic strength?

Answer 10

Increase the current that flows, increase the number of turns in the coil (for the same length of coil), decrease the length of the coil (for the same number of turns) and add an iron core on the inside, becoming an induced magnet.

Question 11

Describe the magnetic field in a solenoid in two ways

Answer 11

Strong and uniform

Question 12

What does the motor effect state?

Answer 12

A current-carrying wire in the presence of a magnetic field will experience a force.

Question 13

What is the formula to calculate the strength of a force?

Answer 13

Force = magnetic flux density x current x length of wire

Question 14

What does a split-ring communtator do?

Answer 14

It swaps the negative and positive connections every half turn, so that the direction of the current is also swapped and the forces acting on the coil will always be acting in the same direction

Question 15

How can the speed of rotations in an electric motor be increased?

Answer 15

Increase current, add more turns in coil, and increase magnetic flux density by using more powerful magnets

Question 16

In the generator effect, how can the size of the induced potential difference be changed?

Answer 16

Change the strength of the magnetic field (stronger magnet), move wire/magnet more quickly and shape the wire into coil to have multiple turns, causing a bigger induced PD

Question 17

What shows the strength of a magnetic field?

Answer 17

The density of the magnetic field lines

Question 18

What is a magnetic material?

Answer 18

A material or object that can be influenced by a magnetic field and has the potential to become a magnet

Question 19

When will a wire not feel a force?

Answer 19

When it is pointing in the same direction as the magnetic field

Question 20

When a wire is induced in a magnetic field and is moved up and down, why does the potential difference disappear when it stops?

Answer 20

Because its the change in the magnetic field that the wire experiences as it moves through it that creates the potential difference

Question 21

What are 3 things that can be done to change the size of the induced potential difference in the generator effect?

Answer 21

Change the strength of the magnetic field, move the wire or magnet more quickly and shape the wire into a coil

Question 22

What current do dynamos produce?

Answer 22

Direct

Question 23

How does an alternator work?

Answer 23

The coil rotates which induces a magnetic field in it. It induces a voltage and current in the coil. The slip rings and brushes ensure there is no swapping every half turn, producing an alternating current

Question 24

How do dynamos work?

Answer 24

The coil spins relative to the magnet, inducing a voltage and a current. The split ring commutators allow swapping every half turn. This means a direct current is produced

Question 25

What is the difference between loudspeakers and microphones? What are similarities?

Answer 25

Loudspeakers use the motor effect and microphones use the generator effect. They both involve alternating currents

Question 26

How do loudspeakers work?

Answer 26

An alternating current flows, causing a magnetic field to appear. This interacts with the permanent magnet’s field, and the interacting fields exert a force on the coil causing it to move back and forth along permanent magnet. This causes the cone to change shape and the magnetic field and force also alternate so vibrations are formed from the moving back and forth. The vibrations are so fast that sound waves are produced

Question 27

How do microphones work?

Answer 27

Sound waves hit the diaphragm and this causes it and the coil to move. The wire will generate a current as it moves in the permanent magnet’s field. The frequency and amplitude of soundwaves determine that of the current

Question 28

How do transformers work?

Answer 28

When supplied with an a.c, the primary will generate an alternating magnetic field, which induces an alternative magnetic field in the iron core. This induces an alternating voltage in the secondary which will lead to an a.c. if the circuit is complete

Question 29

What are the 2 equations used for transformers?

Answer 29

Vp/Vs = Np/Ns and VpIp = VsIs