P5 - Electricity in the home

Question 1

What direction does d.c travel in?

Answer 1

D.c. flows in one direction only.

Question 2

What direction does a.c. travel in?

Answer 2

A.c. repeatedly reverses its direction of flow.

Question 3

What is the UK mains frequency?

Answer 3

50 cycles a second.

Question 4

What is the brown wire connected to?

Answer 4

The live pin.

Question 5

What is wire is the live pin connected to?

Answer 5

Brown wire.

Question 6

What is the blue wire connected to?

Answer 6

The neutral pin.

Question 7

What are the two equations for power (with units)?

Answer 7

Power (w) = energy transferred (J) * time (s)

Power (w) = current (a) x p.d. (volts)

Question 8

How do you work out the period?

Answer 8

Period is the time taken for one complete oscillation (seconds).

Question 9

What is the equation of frequency?

Answer 9

Frequency(Hz) = 1 * period (s)

Question 10

How do you work out the efficiency of an appliance?

Answer 10

Efficiency = Total useful output * Total input

Question 11

How do you work out charge flow?

Answer 11

Charge flow (c) = current (a) x time (s)

Question 12

What is the equation of energy transferred?

Answer 12

Energy transferred = charge (c) x p.d. (v)
E
—————————–
Ch x p.d.

Question 13

Calculate a current across a lamp when the power of the lamp is 0.15W and the p.d. is 1.5V?

Answer 13

Current = 0.15W * 1.5v = 0.1A

Question 14

If a current is 8.3A, what fuse is required?

Answer 14

13A

Question 15

If a current is 2.2, what fuse is required?

Answer 15

3A

Question 16

Explain the role of a step-up transformer.

Answer 16

Increases the voltage and decreases the current which reduces the energy lost.

Question 17

Explain the role of a step-down transformer.

Answer 17

Decreases the voltage and increases the current.

Question 18

Give the definition of the national grid.

Answer 18

A system of transformers and high voltage cables which connect power stations to consumers (home) to provide electricity.

Question 19

Why is it important that the voltage and current are changed at the step up and step down transformers?

Answer 19

So that high voltage transmission lines get the correct voltage and consumers are safe.

Question 20

Give two advantages if burying cables underground?

Answer 20

1. Not affected by bad weather
2. More reliable
3. Hidden from sight
4. Minimal maintenance needed.

Question 21

Give two disadvantages of burying cables underground?

Answer 21

1. Hard to set up
2. Lots of disturbance to land
3. High set up costs
4. Hard to access faults

Question 22

What are the four main stages that happen for power stages to generate electricity?

Answer 22

1. The fuel is burned to boil water to make steam.
2. The steam makes a turbine spin.
3. The spinning turbine turns on a generator which produces electricity.
4. The electricity goes to the transformers to produce the correct voltage.

Question 23

What is the difference between a coal power station and a nuclear power station?

Answer 23

Coal power stations use fuel whereas nuclear power stations use fuel roads containing radioactive waste.

Question 24

Why is a plug made out of plastic?

Answer 24

It is a good electrical insulator and prevents eclectic shocks.

Question 25

Why are the pins of a plug made out of brass?

Answer 25

It is a good conductor of electricity and it is hard.

Question 26

How do you work out the charge of an appliance?

Answer 26

Energy transferred * p.d.

Question 27

What is current measured in?

Answer 27

Amps (A).

Question 28

Charge (C) x potential difference (V) is the equation for finding out what?

Answer 28

Energy transferred.

Question 29

Total useful output * total input is the equation for finding out what?

Answer 29

Efficiency.

Question 30

What is the role of a fuse?

Answer 30

The fuse helps protect the wiring.

If a large current goes through the live wire, the fuse melts and breaks the circuit which switches off the appliance.

Question 31

What is the equation for power (energy transferred)?

Answer 31

Power (W)= energy transferred * time (S)

Question 32

What is the equation for power (current)?

Answer 32

Power (W) = current (A) x p.d. (V)