P5: Electricity in the home

Question 1

What are the two types of current

Answer 1

Alternating current
Direct current

Question 2

What is direct current

Answer 2

Current flowing in one direction

Question 3

What is alternating current

Answer 3

Current flowing in different directions

Question 4

How much is our mains supply in the UK

Answer 4

230V with a frequency of 50 cycles per second (50HZ)

Question 5

What is the period of an AC source

Answer 5

Time taken for a complete oscillation

Question 6

What is the frequency of an AC source

Answer 6

Number of oscillations per second

Question 7

How do we calculate the frequency of an AC source via an oscilloscope

Answer 7

1/period

Question 8

What are the three core cables of the plug

Answer 8

Earth Wire
Live Wire
Neutral Wire

Question 9

What is the live wire

Answer 9

A brown core cable, that carries a 230V potential. It provides the alternating potential difference from the mains electricity supply

Question 10

What is the earth wire

Answer 10

A green and yellow striped core cable that has a 0V potential. It only carries the current if there is a fault. It is a safety wire to stop the electrical appliance from becoming live.

Question 11

What is the neutral wire

Answer 11

A blue core cable that is is close to 0V which is the earth wire’s potential. It completes the circuit and carries current away from the appliance

Question 12

How can we find out the power rating of an appliance

Answer 12

Check the label of the appliance

Question 13

What is the equation that we can use to find the power rating of the appliance

Answer 13

Potential Difference X Current

Question 14

What is the equation that links power, resistance and current

Answer 14

Power = Current X Current X Resistance

Or

Current squared X Resistance

Question 15

How can we calculate the work done per second

Answer 15

We can calculate the energy an appliance transfers with the power rating and equation

Power X Time

Charge flow X Potential Difference

Question 16

What is charge flow and what is it measured in

Answer 16

Charge flow is the amount of charge flowed through a circuit at a given point of time. It is measured in coulombs

Question 17

What is the National Grid

Answer 17

A network of cables and transformers that connect power stations with houses and shops in UK.

Power stations carry an electric current which is an energy carrier

Question 18

Why is a large power station better than a small one

Answer 18

They burn lots more fuel at high temperatures. It creates hot steam that turns turbines
Steam turbines are more efficient at higher temperatures.
Power stations produce electricity at 25000V

Question 19

What is a step up transformer

Answer 19

They increase potential difference and decrease current. Therefore, this transfers less/low energy to the surroundings.

Question 20

What is a step down transformer

Answer 20

They decrease the potential difference and increase the current. This is then delivered to the consumers to use

Question 21

How do fuses and circuit breakers help us

Answer 21

They stop electric current flow if too high. It stops appliance from overheating

Question 22

What is a fuse

Answer 22

They contain a thin wire that melts if the current flowing through an appliance is too high. This breaks the circuit and stops electric flow.

Question 23

What is a circuit breaker

Answer 23

They are special devices that switch off current flow if current is higher than a certain value. We can use them lots of times despite providing the same jobs as fuses. But we must choose them both correctly to allow correct function

Question 24

What are fuse ratings

Answer 24

Tells us the level of the fuse’s melting point. It has a value just above the normal current that an electrical appliance was.

For example if an operating current is 3.9A and fuses with values 3A, 5A and 13A are available, 5A is the best option

Question 25

What are the three types of fuses

Answer 25

3A
5A
15A

Question 26

What is an earthing metal case

Answer 26

They prevent electric shocks. If the case is touched by a wire inside the appliance, the current will flow through the earth wire. As they have a low resistance, a very high current will flow through, breaking the fuse in the device. This prevents current flow and secures the appliance

Question 27

What are the dangers and risk factors of the live wire

Answer 27

They carry so much electrical energy making it dangerous. Even if the power is off, it is dangerous.

Live wires can still be risky when the mains switch is open (plug socket or light is turned off)

As it holds some potential difference

If a live wire is touched, our body supplies a link between the supply and the ground. In short, you get an electric shock.

An electric shock from the mains electricity supply is fatal (can kill you)

If we combine the live wire and the earth wire, the safety feature of the earth wire is removed. This takes a large quantity of current which would overpower our fuse

The fuse will then melt and explode

Question 28

What are sources of direct current?

Answer 28

Batteries
Cells