physics electricity

voltage

(work done/)energy transferred per unit charge

current

rate of flow of charge

resistance

the opposition of a component to the flow of electric current through it

ohms law

voltage is directly proportional to current (with constant physical features)

current in series circuit

are equal

current in parallel circuit

adds up to total

mains

230V, 50Hz

alternating current

produced by electrical generators, has identical terminals

when is earth wire not needed, what does earth wire do

when case is double insulated (non metallic), earth wire is for additional safety (low resistance path to earth)

fuse and circuit breakers use

cut off the flow of electricity

why is it important for a higher rating fuse

so the circuit doesn’t break off small current (undangerous) increases

circuit breaker function

an automatic electromagnet switch every time current exceeds limit

what makes something a good conductor

a metal with delocalised electrons

type of charge in an insulator

no free charge

1mA→?A

0.001

1MA→?A

1,000,000A

polestyrene metal

gains electrons (from duster)

other metal

acetate metal loses electrons to duster (positively charged)

what happens if they have the same charge

repel

what happen if they have opposite charge

attract

how does energy increase of a resistor (example)

free electrons collide within the wire, energy is dissipated into the surrounding (electrical heater, electrical hob)

photocopiers

• image printed onto a positively charged plate

• light falls onto part of the plate, electrical charge leaks away

• negatively charged black toners are attracted to remaining positive areas

• toner is transferred onto paper

• take photo off plate

total resistance

sum of resistance

insecticide sprayers

• for the mist to cover a large area, they are all given the same electrostatic charge as it leaves the sprayer

• so they repel and give a larger surface area

also charged to the negative particles of earth, falls quickly and won’t blow away

risks of static electricity

• electrocution

• fire/explosion due to spark

sparkling of static electricity

charges builds up, large potential difference across a gap

• if large enough, it can travel through objects which creates the spark

static electricity in fueling vehicles, how to prevent danger

• friction by fuel (liquid insulator) and pipes → fuel gains charge

• fuel tank connected to earth by bonding line during refuelling → charge will flow down the bonding line instead