16. P15 Magnetism

Question 1

Permanent magnets

Answer 1

Metal with their own magnetic field

Question 2

Induced magnets

Answer 2

Metals which become magnetic when placed in a magnetic field - lose their magnetism when taken out

Question 3

3 magnetic metals (can be induced)

Answer 3

Iron Nickel Cobalt

Question 4

Direction of magnetic field

Answer 4

North to South

Question 5

magnetic field around a bar magnet

Answer 5

…

Question 6

Describe how you use the right hand rule (cork screw rule)

Answer 6

Align your right hand thumb with the direction of conventional current along the wire, the fingers align to show direction of the circular magnetic field around the wire.

Question 7

The strength of a magnetic field around a solenoid can be increased by…?

Answer 7

1. Increase the size of current through wire, 2. Increase the number of coils, 3. Use an iron core inside the coils (becomes an electromagnet)

Question 8

Describe the shape of the magnetic field inside the coils fo a solenoid.

Answer 8

Strong (lines close together), uniform and parallel (running down the middle of the coils)

Question 9

Describe the shape of the magnetic field around the outside of a solenoid.

Answer 9

Similar to the magnetic field around a bar magnet.

Question 10

To increase the strength of a magnetic field around a current carrying wire.

Answer 10

Coil the wire into a solenoid

Question 11

State what the three fingers represent in Flemings Left Hand Rule.

Answer 11

Thumb = motion/force, First finger = magnetic field direction, middle finger = current

Question 12

Describe what is meant by the motor effect?

Answer 12

When a current carrying wire sits within a permanent magnetic field, the wire experiences a force.

Question 13

What three factors affect the size of the force exerted on a current carrying wire, within a magnetic field.

Answer 13

1) Size of current, 2) Length of wire, 3) Strength of magnetic field.

Question 14

Describe how the electric bell works? (Physics Only)

Answer 14

Person closes switch > circuit is complete current flows > electromagnet is turned on > attracts the iron armature hammer hits the gong > breaks the iron contact > circuit is open > no current flows > electromagnet is demagnetised > armature flicks back into place > circuit is closed again > process repeats

Question 15

Describe how a relay circuit works. (Physics Only)

Answer 15

Person closes switch > current flows in input circuit > electromagnet is turned on > L shaped armature is attracted and so perpendicular end presses switch in output circuit > current flows in output circuit

Question 16

What is the symbol and units for magnetic field strength?

Answer 16

B - measured in Tesla (T)

Question 17

What is the symbol and units for current?

Answer 17

I - measured in Amperes

Question 18

Purpose of a split ring commutator in an electric motor?

Answer 18

It causes the current travelling through the coil, to change direction every half-turn, so motor turns in one direction.

Question 19

How to increase the torque in a motor?

Answer 19

1) Increase current, 2) Increase number of coils, 3) Increase strength of permanent magnets (magnetic field)

Question 20

How loudspeakers work (Physics Only)

Answer 20

The current flows through the solenoid produces a magnetic field which its size and direction depend on the current flowing. This coil is placed in the middle of the permanent magnetic field, so the wires experience a force and move depending on the direction and size of the current. This makes the cone vibrate and produce sound.

Question 21

The generator effect (Physics Only)

Answer 21

If a wire moves with respect to a magnetic field, the changing field cutting the wire induces a current in the wire.

Question 22

To increase the size of the current induced as it moves through a magnetic field (Physics Only)

Answer 22

1) Move the wire/coil faster, 2)Stronger magnetic field, 3) coil the wire with more turns.

Question 23

What do the slip rings and brushes do in an AC generator (Physics Only)

Answer 23

The slip rings allow the frame(coils of wire) to turn with out permanent wire connections getting tangled

Question 24

How alternators work (alternating current) (Physics Only)

Answer 24

The magnet rotates, meaning the direction of the magnetic field is changing, thus inducing an alternating current

Question 25

DC Generator graph (Physics Only)

Answer 25

The current is always positive (always going in the same direction) but increases and decreases in value as the wire is upright to the magnetic field before rotating back into being parallel with the current still going in the same direction, due to the commutator

Question 26

AC Generator graph (Physics Only)

Answer 26

The current alternates between positive and negative (switches directions) as the magnet continuously turns, thereby changing the direction of the magnetic field, thus changing the direction of the current

Question 27

Transformers

Answer 27

Transformers are used to increase the current from a power input to an output

Question 28

How transformers work

Answer 28

A transformer consists of an iron core with a primary coil and a secondary coil

Question 29

Why do transformers only work with an alternating current?

Answer 29

The alternating current, creates a magnetic field which is continuously changing direction, which provides the movement required to induce the voltage in the secondary coil

Question 30

Step up transformers have more/fewer turns on the secondary

Answer 30

more

Question 31

Step down transfers have more/fewer turns on the secondary

Answer 31

fewer

Question 32

How to work out the change in voltage

Answer 32

[No. of turns (primary coil)] ÷ [No. of turns (secondary coil)] = [Voltage (primary coil)] ÷ [Voltage (secondary coil)]