P5

Question 1

what is the frequency of mains electrical supply

Answer 1

50 hertz, delivered to homes at 230 V

Question 2

what is the function of the live wire

Answer 2

copper wire coated with brown plastic along which the current enters the device

Question 3

what is the function of the neutral wire

Answer 3

copper wire coated with blue plastic that connects to the cable in the wall and completes the circuit

Question 4

function of the earth wire

Answer 4

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

Question 5

function of outer insulation

Answer 5

all 3 wires in the cable are bundled together and there is extra plastic insulation wrapped round them all for safety

Question 6

function of the cable grip

Answer 6

holds cable tightly in place so wires do not become loose

Question 7

function of fuse

Answer 7

glass or ceramic cannister containing a thin wire that melts if current gets too high

Question 8

what are step up transformers

Answer 8

used at power stations to trasfer electricty to the national grid used to make the size of lternating potential difference bigger

Question 9

what are step down transformers

Answer 9

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

Question 10

what is the peak potential difference of an a.c supply

Answer 10

maximum volatge measured from 0 volts

Question 11

describe the current of a live wire

Answer 11

alternating so alternately positive and negative every cycle

Question 12

how do you measure the frequency of an a.c supply

Answer 12

measure the time period of the waves then use the equation freq= 1/ time taken for one cycle

Question 13

why are the pins of a plug made of brass and not copper

Answer 13

it is a good conductor, doesn’t rust or oxidise. copper is a better conductor but isn’t as hard

Question 14

why is copper used for the wires

Answer 14

good conductor and bends easily

Question 15

why are the cables that join toghether wall sockets thicker than cables that join together light fittings

Answer 15

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

Question 16

what is a short circuit

Answer 16

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

Question 17

what are the 3 equations for power

Answer 17

energy transferred/ time 
or
current x potential difference 
or 
current^2 x resistance

Question 18

what is current

Answer 18

the charge that flows through an electrical appliance each second

Question 19

what is potential difference

Answer 19

the energy transferred to the appliance by each coulomb of charge that passes through it

Question 20

what is power

Answer 20

energy transferred to an appliance by an electric current every second

Question 21

what is the equation for charge `

Answer 21

current x time

Question 22

what is the equation for efficiency

Answer 22

output power/ input power x100

Question 23

how would increasing the potential difference and the frequency affect the oscillations of an oscillator

Answer 23

pd: oscillations would be taller
freq: more cycles seen on screen

Question 24

why are wall sockets in a room connected in parallel

Answer 24

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