P11 , P12 AND P13

Magnetic poles

Unlike poles attract, like poles repel

Magnetic materials

Cobalt, steel, iron, nickel

Permanent magnet

Always produce their own magnetic field

Magnetic force vs. distance

Force decreases as distance increases

Magnetic field around a bar magnet is

Strongest at the poles

Direction of magnetic field lines

From North to South

Concentration of field lines

Closer lines indicate stronger magnetic field

Plotting compass

Used to show magnet field shape and direction

Using a plotting compass

Mark field direction, move compass, connect lines

Earth's magnetic field

Generated by the magnetic outer core

induced magnet

only produce a magnetic field in the presesence of another magnet

magnet

any material or object that produces a magnetic field

the force between permanent and induced magnet

always attractive

magnetically soft material

loses/gains magnetism slowly

magnetically hard material

loses/gains magnetism quickly

what diagram is this

2 sideways magnet attraction

what diagram is this

poles attraction

what diagram is this

poles repulsion

what diagram is this

uniform magnetic field

step up transformers

increase voltage, decrease current

step down transformers

decrease voltage, increase current

journey of electricity In national grid

power stations - step up transformer - pylons - step down transformer- homes

in a step up transformer what side has more coils

secondary coil

how do transformers work

when supplied with alternating current , it then induces an alternating magnetic field in the iron core which induces an alternating current in the secondary core

Fleming right hand rule

point your thumb to the direction of the current, the direction your fingers are curled in is the magnetic field direction .

Fleming left hand rule

a : direction of force
b: direction of magnetic field
c: direction of current

what can flemings left hand rule tell us

the direction of the force experienced by a current carrying wire in a magnetic field.

motor effect

current carrying wire in a magnetic field will experience a force

how does an electric motor work

a coil of wire carrying current in placed in a magnetic field, it then turns due to the motor effect. Then a split-ring commutator is used to change the direction every half turn so it turns fully

electromagnetic induction

a potential difference is generated in a wire due to a change in magnetic field

how can I increase voltage by electromagnetic induction

increase magnetic field strength, more coils, move magnet faster

what’s the difference between an alternator and dynamo

dynamo has a split ring commutator by an alternator has slip rings and brushes

what does the dynamo produce

direct current as it changes direction every half-spin

what does an alternator produce

alternating current

static electricity

when two objects are rubbed together, the friction causes electrons to move building up charge

does static electricity work for conducting materials?

no as the electrons will flow back again

what does an electric field cause

a charge to feel a force

what direction do the field lines go in a positive point charge

outwards

what direction do the field lines go in a negative point charge

inwards

what does the distance between field lines tell you in an electric field

strength of the field

what is true about the electrical field between two parallel plates

it is uniform

what can be used to prevent electrostatic charge building up

earthing

how does earthing prevent electrostatic charge building up

charged object is connected to ground using a conductor, it provides a low resistance route for charges

how does the charge affect travel of electrons in earthing

electrons flow up to the conductor if its positive charge, and flow down to earth if its negative charge

what are 2 uses of static electricity

photocopiers , insecticide sprayers

how do photocopiers use static electricity

copies images onto a charged plate before printing them

how do insecticide sprays use static electricity

insecticide has an electrostatic charge so they all repel each other and cover a larger surface area

danger of static electricity

build up of static charge could mean that fuel gains charge when vehicle is being fuelled so if the charge causes a spark - it can ignite and explode

what is a spark

when electrons jump across the gap between a charged object and the earth

transformer equation for power across the 2 coils

Vp Ip = Vs Is

equation linked with turns of primary and secondary coil with voltage

Vp/Vs = Np/Ns

why are step up transformers used

increases voltage to reduce heat loss and increase efficiency

why are step down transformers used

decreases voltage to make it suitable for homes