MAGNETISM + ELECTROMAGNETISM

Question 1

what is induction?

Answer 1

when a wire passes through a magnetic field line and voltage is induced

Question 2

magnetic materials:

Answer 2

• iron
• cobalt
• nickel

Question 3

how is magnetism induced in some materials?

Answer 3

when they are placed into a magnetic field

Question 4

what are magnetic field lines?

Answer 4

show the direction that a magnet would point

Question 5

what direction do magnetic field lines go from?

Answer 5

North to South

Question 6

can magnetic field lines cross?

Answer 6

no

Question 7

what is an electromagnet?

Answer 7

any current carrying wire

Question 8

P2 how are electromagnets made ?

Answer 8

by winding coils of wire, you can turn them on and off

Question 9

how to increase the strength of a magnetic field?

Answer 9

• wind more coils
• insert a magnetic core
• use a higher current

Question 10

how to use two magnets to produce a magnetic field around them:

Answer 10

North Pole facing South Pole

Question 11

P2 what is there on a charged particle when it moves in a magnetic field as long as its motion is not parallel to the field?

Answer 11

a force

Question 12

what are the properties of a magnetically hard material?

Answer 12

hard to magnetise but retains magnetism better

Question 13

what are the properties of a magnetically soft material?

Answer 13

easy to magnetise but lose magnetism easily

Question 14

why is a force exerted on a current-carrying wire in a magnetic field in simple d.c. electric motors ?

Answer 14

• Current flows in the wire/coil.
• This creates a magnetic field around the wire/coil.
• This magnetic field interacts with the field from the permanent magnet.
• This produces a force on the wire/coil which moves the wire/coil.
• The split-ring communicator changes the direction of the current every half turn as it spins.
• This reverses the direction of the forces, allowing the coil to continue spinning.

Question 15

why is a force is exerted on a current-carrying wire in a magnetic field in simple a.c. loudspeakers?

Answer 15

• An alternating current from the source passes though the coils in the speaker.
• This current is constantly changing direction and magnitude
• This current creates a magnetic field around the coil
• This field interacts with the magnetic field from the permanent magnets
• Creating a constantly changing force on the coil.
• This causes the coil to vibrate in and out as the direction of the force changes, moving the cone
• The cone causes vibrations which we hear as sound waves.

Question 16

what does the first finger represent in FLHR?

Answer 16

magnetic field direction

Question 17

what does the middle finger represent in FLHR?

Answer 17

direction of current

Question 18

what does the thumb represent in FLHR?

Answer 18

direction of force

Question 19

how does the force on a current-carrying conductor in a magnetic field change with the magnitude and direction of the field and current?

Answer 19

• If you increase the magnitude of the current through a wire or the size of the magnet being used, you increase the force on the wire.
• If you change the direction of the current or reverse the poles of the magnet, you change the direction of the force on the wire

Question 20

when is voltage induced in a current or coil?

Answer 20

when it moves through a magnetic field or when a magnetic field changed through it

Question 21

how can you induce a voltage?

Answer 21

changing the strength of a magnetic field

Question 22

factors affecting current:

Answer 22

• strength of the magnetic field
• increase the numbers of wire being cut (use coils rather than a single wire)
• increase the speed of the movement or rotation of the wire and magnetic field relative to eachother

Question 23

how do we generate electricity?

Answer 23

rotating a magnet within a coil of wire and of a coil of wire within a magnetic field

Question 24

P2 describe the structure of a transformer:

Answer 24

• work by passing a magnetic field between two coils
• primary coil creates an alternating magnetic field (as it is connected to AC supply)
• the alternating magnetic field passes around inside the transformer’s core
• the alternating magnetic field creates a voltage in the secondary coil

Question 25

uses of induction:

Answer 25

• induction hob
• wireless charging

Question 26

P2 what are step up transformers used for?

Answer 26

Step-up transformers are used to increase the potential difference from the power station to the transmission cables

Question 27

P2 what are step down transformers used for?

Answer 27

Step-down transformers are used to decrease the potential difference, to a much lower value, from transmission cables for domestic use (houses, offices, shops)

Question 28

P2 relationship between input (primary) and output (secondary) voltages and the turns ratio for a transformer:

Answer 28

input (primary) voltage/ output (secondary) voltage = primary turns/ secondary turns

Question 29

P2 relationship between input power and output power:

Answer 29

input power = output power
voltage (p) x current (p) = voltage (s) x current (s)