Revision topic 16

Question 1

what are the two wires that are in every main circuit?

Answer 1

live wire and neutral wire

Question 2

what happens in the mains circuit

Answer 2

the current through main appliance alternate as mains power supply to provide an altering potential difference between these two

Question 3

what is the neutral wire

Answer 3

it is an earthed wire at the substation

Question 4

what is the name of the difference between the live wire and the neutral wire

Answer 4

voltage or potential of the live wire

Question 5

why is the live wire dangerous

Answer 5

because it constantly keeps changing from - to + and back every cycle

Question 6

what is oscilloscope

Answer 6

it is a device used to find the peak potential difference and frequency of a low voltage a.c supply

Question 7

the frequency of a.c supply =

Answer 7

1/time taken for 1 cycle

Question 8

the peak potentail diffrence =

Answer 8

v x Height

Question 9

why are all mains circuit made of hard-wearing electrical circuits

Answer 9

because the plugs sockets and cables all contain a live wire which is dangerous and can electrocute someone

Question 10

what are sockets made of

Answer 10

they are made of stiff plastics material with wire inside them, which includes a live wire an earth wire and a neutral wire, all the wires are parallel to each other so if appliances can be turned off without effecting others

Question 11

what is the earth wire

Answer 11

it is a circuit connected to the ground of your home

Question 12

what are plugs made off?

Answer 12

stiff plastic material

Question 13

what is inside the plug

Answer 13

a live pin the earth pin, and the neutral pin stick out through the plug which is all made of copper since it is a good conductor and doest rust, and the wires are sealed and cant touch each other, and the plug contains a fuse between the live pin and the live wire so if too many current passes through it would melt and cut off the life wire

Question 14

what are cabled used for

Answer 14

they are used for main appliances

Question 15

what is cables made from

Answer 15

they are made from 2 or 3 insulated copper wires that are surrounded with flexible plastic to protected anyone from receiving an electrical shock when they touch it, the wires are color-coded to distinguish between them

Question 16

why is copper used in cable

Answer 16

because it is a good conductor of heat and it bends easily

Question 17

cables of different thicknesses..?

Answer 17

are used in different cases

Question 18

what does the fuse contain

Answer 18

the fuse contains a thin wire that would heat up and melt if the current is larger than the rating of the fuse

Question 19

what is the rating of the fuse

Answer 19

it is the maximum amount of current that can pass through the wire without melting it

Question 20

the fuse is within series with?

Answer 20

the live wire so if the fuse the appliance would then be cut off from the live wire

Question 21

why is it important to have the right current rating

Answer 21

because if the current rating is too high I wouldn’t fuse when it should do, the heating effect from the large dose of current would cause appliances and cables to catch on fire, in order for the cable to make the heating effect insignificant it needs to be thicker, as the higher the current rating the thicker the cable must be

Question 22

why is earthing a wire important

Answer 22

to stop it from electrocuting anyone

Question 23

which one has greater current an earthed heater that touches the frame or an earthed heater that doesn’t touch the frame and why

Answer 23

the earthed heater isn’t touching the frame since it goes through part of the heating element

Question 24

what is a circuit breaker?

Answer 24

it is an electromagnet in series to a switch that would open when there is too much current passing by once it opens it would stay open unless someone can reset it, this can happen if there is a fault with the appliance that is in series with the circuit breaker.

Question 25

power =

Answer 25

energy transfer/ time

Question 26

the rules for any electrical appliance

Answer 26

1. the current through it is the charge that flows through it every second
2. potential difference across it is the energy transferred to the appliance
3. power supply is the energy transferred per second

Question 27

power supply =

Answer 27

current x potential difference

Question 28

charge =

Answer 28

current x time

Question 29

when an electrical appliance is on

Answer 29

electrons would be forced through the appliance by the potential difference of the power supply

Question 30

what happens when an electrical flow passes through a resistor

Answer 30

the energy would be transferred to a resister making it hotter

Question 31

the energy transfer in a certain time in the resistor depends on?

Answer 31

the charge passing through it, and the potential difference across it hence:
energy transferred = potential difference x charge

Question 32

when a charge flows around the circuit at a certain time the energy supplied from the battery would equal

Answer 32

the energy transferred to all components n the circle

Question 33

for any appliance the energy supplied depend on

Answer 33

1. how long it was switched on

2. the power supplied to it

Question 34

energy transferred (kWh) =

Answer 34

power x time

Question 35

what is a kilowatt-hour

Answer 35

it is the energy supplied to 1kW in 1 hour

Question 36

what is the electricity meter

Answer 36

in measures electrical energy we use. and to find the cost of the electrical bill we take the number of kWh used x the cost per kWh

Question 37

what are precautions you should take for electrical faults

Answer 37

if a fuse blows or a circuit breaker blows when using the main appliance turn it off and don’t use it again unless it’s been checked or if an appliance gets overheated for who smell burning from it again don’t use it until you check it

Question 38

an electrician selecting a cable for an appliance needs to use

Answer 38

1. two-core cable if the appliance is double-insulated and no earth wire is required
2. a three-core cable if an earth wire is needed because the case is made of metal
3. a cable with conductors of suitable thickness so the heating effect of the current is insignificant

Question 39

why is filament bulb is very inefficient

Answer 39

because the energy from the hot bulb would gradually make the plastic parts of the bulb brittle and they crack

Question 40

where are low-energy bulbs more efficient and what are the examples of them

Answer 40

they are more efficient because they dont heat up.

examples:

1. CFLs - which are often used for room lighting over filament bulb
2. LEDs operate at low voltage and power they are much more efficient than filament and halogen bulb and they last longer