electromagnetism

Question 1

what happens when a current flows through a wire?

Answer 1

a magnetic field is produced around the wire

Question 2

what does the strength of the magnetic field depend on?

Answer 2

the current through the wire and the distance from the wire

Question 3

how can you increase the strength of a magnetic field?

Answer 3

increase the current, move closer to the wire

Question 4

what is the shape of magnetic field around a wire?

Answer 4

concentric circles perpendicular to the wire

Question 5

describe the right hand thumb rule

Answer 5

• thumb shows direction of current + to -
• finger point in N - S
• fingers curl in direction of magnetic field

Question 6

what is a solenoid?

Answer 6

a long coil of insulated wire

Question 7

why does a solenoid produce a stronger mag field than if the wire was straight?

Answer 7

• field lines around each loop of wire line up with each other
• results in lots of field lines pointing in the same direction that are very close together
• the closer field lines are, the stronger the field is

Question 8

describe the field inside a solenoid and why?

Answer 8

strong and uniform
strong: several magnetic lines close together
uniform: magnetic field lines are in the same direction

Question 9

describe the field outside a solenoid

Answer 9

similar to a bar magnet, curves

Question 10

how can you increase strength of mag field of a solenoid?

Answer 10

• adding a iron core
• increase current / number of turns in coil
• move closer

Question 11

why does an iron core increase strength?

Answer 11

• it becomes an induced magnet whenever current is flowing

Question 12

what is an electromagnet?

Answer 12

a solenoid with an iron core

Question 13

dot in middle of circle v cross in middle meaning

Answer 13

dot: current flowing towards you (out of paper)
cross: current flowing away from you (into paper)

Question 14

what happens if you reverse current?

Answer 14

magnetic field reverses

Question 15

why are electromagnets useful?

Answer 15

they can be turned off

Question 16

hard core v soft core

Answer 16

hard: doesn’t immediately switch off
soft: immediately switches off

Question 17

how are electromagnets used in cranes in scrapyards?

Answer 17

they can be switched on to pick stuff up then off to drop it

Question 18

how does a relay work?

Answer 18

1. contains two separate circuits: high voltage and low voltage
2. low voltage contains a switch and electromagnet which is safe to be turned on and off
3. high voltage contains two metal contacts instead of switch, one contact is connected to spring which keeps them apart, and an iron block next to spring
4. when switch not closed, no current flows through low voltage as circuit is broken, also means no current flows through high voltage as contacts aren’t touching so also broken
5. when switch is closed, current flows through, so now magnetic field around electromagnet, this attracts iron block causing contacts to close so switches on high voltage circuit