P5 Flashcards
what is the frequency of mains electrical supply
50 hertz, delivered to homes at 230 V
what is the function of the live wire
copper wire coated with brown plastic along which the current enters the device
what is the function of the neutral wire
copper wire coated with blue plastic that connects to the cable in the wall and completes the circuit
function of the earth wire
copper wire coated in striped plastic that provides a path for current to flow from the case of the device to the ground if there is a fault
function of outer insulation
all 3 wires in the cable are bundled together and there is extra plastic insulation wrapped round them all for safety
function of the cable grip
holds cable tightly in place so wires do not become loose
function of fuse
glass or ceramic cannister containing a thin wire that melts if current gets too high
what are step up transformers
used at power stations to trasfer electricty to the national grid used to make the size of lternating potential difference bigger
what are step down transformers
used to supply electricity from the national grid to consumers. homes and offices are supplied with a lower power than factories that use more power
what is the peak potential difference of an a.c supply
maximum volatge measured from 0 volts
describe the current of a live wire
alternating so alternately positive and negative every cycle
how do you measure the frequency of an a.c supply
measure the time period of the waves then use the equation freq= 1/ time taken for one cycle
why are the pins of a plug made of brass and not copper
it is a good conductor, doesn’t rust or oxidise. copper is a better conductor but isn’t as hard
why is copper used for the wires
good conductor and bends easily
why are the cables that join toghether wall sockets thicker than cables that join together light fittings
more current passes along the wall socket cables so wires need to be thicker so they have less resistance which stops the heating affect of the current making the wires too hot
what is a short circuit
when a live wire touches a neutral wire, a big current passes through the wires at the point of contact. this cuts the current off as the fuse blows
what are the 3 equations for power
energy transferred/ time or current x potential difference or current^2 x resistance
what is current
the charge that flows through an electrical appliance each second
what is potential difference
the energy transferred to the appliance by each coulomb of charge that passes through it
what is power
energy transferred to an appliance by an electric current every second
what is the equation for charge `
current x time
what is the equation for efficiency
output power/ input power x100
how would increasing the potential difference and the frequency affect the oscillations of an oscillator
pd: oscillations would be taller
freq: more cycles seen on screen
why are wall sockets in a room connected in parallel
so they can be switched on and off independantly and if they were in series the pd would depend on the resistance of each appliance
