Chapter 5 Electricity in the Home

Question 1

What is an alternating current (a.c.)?

Answer 1

An electric current in a circuit that repeatedly reverses its direction

Question 2

What is a direct current (d.c.)?

Answer 2

An electric current in a circuit that is in one direction only

Question 3

What is an earth wire?

Answer 3

The wire in a mains cable used to connect the metal case of an appliance to earth

Question 4

What does a fuse do?

Answer 4

A fuse contains a thin wire that melts and cuts the current off if too much current passes through it.

Question 5

What is a live wire?

Answer 5

The mains wire that has a voltage that alternates in voltage (between +325V and -325V in Europe)

Question 6

What is a neutral wire?

Answer 6

The wire of a mains circuit that is earthed at the local substation so its potential is close to zero

Question 7

What is a oscilloscope?

Answer 7

A device used to display the shape of an electrical wave

Question 8

What is a plug used for?

Answer 8

A plug has an insulates case and is used to connect the cable from an appliance to a socket.

Question 9

What are step-down transformers?

Answer 9

An electrical device used to step-down the size of an alternating potential difference

Question 10

What are step-up transformers?

Answer 10

An electrical device used to step-up the size of an alternating potential difference

Question 11

What is a three-pin plug?

Answer 11

A three-pin plug has a live pin, a neutral pin and an earth pin.

Question 12

What is the power grid?

Answer 12

The Power Grid is how the electricity gets to the homes

Question 13

Mains supply is DC or AC

Battery supply is DC or AC

Answer 13

ac

dc

Question 14

What is the frequency of the ac mains supply?

Answer 14

50 cycles per second or 50HZ (hertz)

Question 15

Every mains circuit has a _________ wire and a __________wire

Answer 15

live

neutral

Question 16

The oscilloscope is used to display the potential difference of an alternating potential difference supply unit . How would the trace change if THE POTENTIAL DIFFERENCE IS INCREASED

Answer 16

waves taller

as amplitude increases

Question 17

The oscilloscope is used to display the potential difference of an alternating potential difference supply unit . How would the trace change if THE FREQUENCY IS INCREASED

Answer 17

waves closer together

as time for each cycle is less

Question 18

Give a reason why a mains appliance with metal case is unsafe if the case is not earthed

Answer 18

if live wire touches case, case becomes live

anyone touching case electrocuted as electric current passes through their body to earth

Question 19

Write the colour of each wire in a mains circuit

Answer 19

live: brown, neutral: blue, earth: green and yellow

Question 20

Why are the wall sockets in a room connected in parallel with each other

Answer 20

so any appliance connected to wall socket can be switched on or off, without affecting any appliance connected to a different wall socket

Question 21

A small hairdryer has a double- insulated plastic case and is fitted with a plastic mains cable that contains two wires that are insulated separately. Name the two wires?

Why are the two wires in the cable insulated separately?

Answer 21

the live wire and the neutral wire

the live wire is at 230 V and the neutral wire is approximately at 0 V
they are insulated from each other to stop the metal of the wires making contact
if this happened, a very large current would pass between the wires and the heating effect would cause a fire.

Question 22

describe the National Grid

Answer 22

• a system of cables and transformers

- a system linking power stations to houses

Question 23

Describe the difference between a step up and step down transformer

Answer 23

a step-up transformer increases the size of an alternating
potential difference
a step-down transformer decreases the size of an
alternating potential difference

Question 24

What is the advantage of having a step up transformer in a system? 3 marks

Answer 24

with a step-up transformer between the power station and
the grid cables, power is transferred much more efficiently than if the transformer was not included.
This is because the greater the potential difference is, the smaller the current in the cables is so the smaller the resistance.
heating effect of the current in the cables is for the same
amount of power transferred.

Question 25

What is meant when something is said to be double insulated?

Answer 25

the outer case of the appliance is made of plastic

and the wires inside are covered in plastic

Question 26

Why might a person get an electric shock if the cables in a electric mower get cut whilst mowing?

Answer 26

-the live wire is still live with a potential difference of 230 volts
-the human body is at earth potential difference of 0 volts
-therefore if the gardener touches the live wire an electric
current will flow through him to earth

Question 27

What does an electricity meter measure?

Answer 27

how much energy is supplied

Question 28

When charge flows through a resistor, energy is transferred to the ____________, so the resistor becomes HOTTER/COLDER

Answer 28

resistor

hotter

Question 29

Why is copper used for wires?

Answer 29

• good electrical conductor

- bends easily

Question 30

What wires are inside a three-pin plug

Answer 30

-earth
-live
-neutral
and a fuse