Electricity in the home

Question 1

What is the National grid?

Answer 1

It is a network of cables, pylons and transformers.

Question 2

What is the function of the National grid?

Answer 2

Its function is to deliver electricity to homes, schools, offices and factories.

Question 3

How does the National grid do its function?

Answer 3

It does this in the most efficient way possible, that is by reducing the energy loss across cables as heat.

Question 4

What does a step up transformer do?

Answer 4

Increases the p.d, but decreases the current; a lower current reduces heat loss.

Question 5

What is the equation for power loss?

Answer 5

P = I^2R

Power (Watts) = Current^2 (Amps) x Resistance (Ohms)

Question 6

What does the live wire do?

What colour is the live wire in a mains plug?

Answer 6

The electricity goes in and is transferred from the power station to the user.

Brown

Question 7

What does the neutral wire do?

What colour is the neutral wire in a mains plug?

Answer 7

The electricity goes out and is transferred from the user to the power station.

Blue

Question 8

Where does the earth wire go?

What colour is the earth wire in a mains plug?

Answer 8

It goes into the ground through a large conductive hole.

Yellow and green

Question 9

Why are most of the plug and cable externally made from plastic?

Answer 9

For their insulation properties.

Question 10

The brass pins connected to the plug are…

Answer 10

good conductors and are strong, resilient and rust resistant.

Question 11

Inside the plug how does electricity flow through it?

Answer 11

electricity enters via the pin connected to the brown wire, and then onto the appliance. Then it is connected to the blue as the output back to the socket.

Question 12

What does the Earth ensure if a live connection at the appliance touches the metal casing?

Answer 12

There is a surge of current that can be transferred away. (Assuming the fuse doesn’t blow first).

Question 13

What is the equation for Power in terms of energy and time?

Answer 13

P = E / t

Question 14

P = E / t rearranged is E = Pt and this expression is used to determine?

Answer 14

the energy used by an appliance in a specific time. E.g. A filament lamp (100W) is switched on for 30 minutes. How much energy will it use?

Question 15

What is the equation for efficiency?

Answer 15

Efficiency = useful energy/power output / total energy input (x100)

Question 16

What does energy equal in terms of current, voltage and time.

Answer 16

E = IVt

Question 17

What is alternating current?

Answer 17

a current that changes direction repeatedly; every 0.025 / 50 times per second.

Question 18

What is direct current?

Answer 18

a current that flows from the positive to the negative terminal.

Question 19

What is amplitude?

Answer 19

Maximum displacement of the wave.