electromagnetism

what does a current travelling through a wire produce

a magnetic field

how to increase the strength of mag field in a wire

increase I

coil the wire

iron core

flemings left hand rule

what do crosses on a diagram mean

fierld lines going into the page

what do dots on a diagram mean

field lines coming out of the page

equation for magnetic flux density

equation for force using magnetic flux density

F = BIL

magnetic flux density

the force of 1 wire carrying a current of 1 amp at right angles to the magnetic field

difference between direction of electron and direction of conventional current

conventional current is opposite current flow

convential - positive to negative

electrons - negative to positive

equation for radius of charged particle in field

r = mv/bq

force on charged particles as it enters a mag field

F = BqV

how to generate a voltage using wire and magnet

moving the wire next to a magnet generates a voltage, if its a complete circuit then current will flow

what affects the size of the induced EMF

No of coils

size of magnetic field

speed (change of flux)

Faraday’s law

the induced EMF is directly proportional to the rate of change of flux linkage

equation for flux linkage

equation for induced emf

Lenz’s law

the induced emf is always in a direction that opposes the change that caused it

voltage over time graph for a magnet moving through coil at constant speed

voltage over time graph for a magnet falling through a coil

how does a transformer work

1. alternatinc current produces an alternating mag field

2. iron core increases field lines

3. magnetic flux is linked to the secondary coil by the iron core

4. changing magneticc flux induces emf over the secondary coil

5. more turns on secondary coil increase the rate of change of flux linkage

what is done to the iron core to prevent it from overheating

it is laminated, sliced and insulator glue prevents large currents

eddy currents

swirling loops of current induced by conductors

back emf

emf which opposes the change that caused it

ring experiment

current produces a mag field around the aluminium ring

the direction of the ring field opposes the change that caused it

this causes the ring to float

mains electricity Vrms

voltage (root mean square voltage), a way to express the average power of an AC signal in terms of DC voltage equivalant

easier for calculations

UK - 230V which is lower than its peak of 325V

how to calculate RMS voltage or current

V/Irms = V/Ipeak divided by root 2