electromagnetism Flashcards
what happens when a current flows through a wire?
a magnetic field is produced around the wire
what does the strength of the magnetic field depend on?
the current through the wire and the distance from the wire
how can you increase the strength of a magnetic field?
increase the current, move closer to the wire
what is the shape of magnetic field around a wire?
concentric circles perpendicular to the wire
describe the right hand thumb rule
- thumb shows direction of current + to -
- finger point in N - S
- fingers curl in direction of magnetic field
what is a solenoid?
a long coil of insulated wire
why does a solenoid produce a stronger mag field than if the wire was straight?
- 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
describe the field inside a solenoid and why?
strong and uniform
strong: several magnetic lines close together
uniform: magnetic field lines are in the same direction
describe the field outside a solenoid
similar to a bar magnet, curves
how can you increase strength of mag field of a solenoid?
- adding a iron core
- increase current / number of turns in coil
- move closer
why does an iron core increase strength?
- it becomes an induced magnet whenever current is flowing
what is an electromagnet?
a solenoid with an iron core
dot in middle of circle v cross in middle meaning
dot: current flowing towards you (out of paper)
cross: current flowing away from you (into paper)
what happens if you reverse current?
magnetic field reverses
why are electromagnets useful?
they can be turned off
hard core v soft core
hard: doesn’t immediately switch off
soft: immediately switches off
how are electromagnets used in cranes in scrapyards?
they can be switched on to pick stuff up then off to drop it
how does a relay work?
- contains two separate circuits: high voltage and low voltage
- low voltage contains a switch and electromagnet which is safe to be turned on and off
- 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
- 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
- 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
