Chapter 17 - Household Electricity

Question 1

What is the difference between DC and AC

Answer 1

DC is in one direction

AC is repeatedly reversing its direction

Question 2

What is the type of current, max and min voltage and frequency in mains electricity?

Answer 2

AC, +325V -325V, 50Hz

Question 3

What can a diode do to an AC

Answer 3

Can be used for half wave rectification. AC->DC

Question 4

Where would you measure the peak voltage?

Answer 4

From the peak voltage to zero volts

Question 5

Why is plastic used as a case for sockets and plugs?

Answer 5

Good insulator and reasonably cheap

Question 6

What is a mains cable made out of

Answer 6

2 or 3 insulated copper wires surrounded by a layer of plastic material. Wires are Live, Earth and Neutral

Question 7

In a plug, what wire is the brown wire and where is it in the plug?

Answer 7

Live and on the in right

Question 8

In a plug, what is the striped yellow and green wire and where is it in the plug?

Answer 8

Earthed wire and at the top

Question 9

In a plug, what is the blue wire and where is it in the plug?

Answer 9

Neutral and on the left

Question 10

Why is copper used in the wires of a plug?

Answer 10

Good conductor and bends easily

Question 11

What does a fuse contain?

Answer 11

A thin wire with a certain resistance

Question 12

What happens to the wire in a fuse if the current becomes too high?

Answer 12

It heats up, melts and cuts off the current (breaks circuit)

Question 13

Where is the fuse fitted in the plug?

Answer 13

In series with the live wire

Question 14

Why is the fuse fitted in series with the live wire?

Answer 14

Because if it blows, the appliance won’t become live from the live wire

Question 15

What is a circuit breaker?

Answer 15

An electromagnetic switch that opens and breaks the circuit if too much current passes through it

Question 16

When do you not need to earth an appliance?

Answer 16

When the appliance has a plastic case because plastic is an insulator and can’t become live

Question 17

Why would you use a circuit breaker over a fuse?

Answer 17

Circuit breakers work faster and can be reset more quickly and conveniently

Question 18

Why would you use a Residual Current Circuit Breaker over a Circuit Breaker?

Answer 18

RCCB is more sensitive

Question 19

What is the power supplied to a device

Answer 19

The energy transferred to it every second

Question 20

What is the potential difference supplied to a device?

Answer 20

Energy transferred to the appliance by each coulomb of charge that flows through it

Question 21

What is the current supplied to a device?

Answer 21

The charge that flows through it each second

Question 22

What are the standard fuses for domestic appliances?

Answer 22

3A, 5A, 13A

Question 23

What happens when an electrical charge flows through a resistor

Answer 23

It heats up due to energy being transferred to the resistor

Question 24

What does the energy transferred to a resistor depend on?

Answer 24

Amount of charge that passes through it

The P.D across the resistor

Question 25

What is a Kilowatt-Hour?

Answer 25

The energy supplied to a one kW appliance in 1 hour

Question 26

Why are electrical faults dangerous?

Answer 26

They can cause fires and electric shocks

Question 27

What is the National Grid

Answer 27

A network of cables and transformers that distributes electricity

Question 28

When are step up transformers used?

Answer 28

To raise the power station voltages to grid voltages

Question 29

When are step down transformers used?

Answer 29

To lower the grid voltage for use in industries and homes

Question 30

What is the benefit of a high grid voltage?

Answer 30

It reduces the current needed, reducing energy loss, making the system more efficient