Power and electrical appliances

Question 1

Which wire in a plug is brown?

Answer 1

live wire

Question 2

Which wire in a plug is blue?

Answer 2

Neutral wire

Question 3

Which wire in a plug is green and yellow?

Answer 3

Earth wire

Question 4

Which wire in a plug is red?

Answer 4

None

Question 5

What is the purpose of an earth wire?

Answer 5

to carry away electrical charge from the casing of an appliance to prevent it from giving electric shocks

Question 6

Which two wires are at 0 Volts?

Answer 6

earth and neutral wires

Question 7

What is the voltage of the live wire?

Answer 7

230 V

Question 8

What is the function of the live wire?

Answer 8

it provides alternating potential difference from the mains supply

Question 9

What is the function of the neutral wire?

Answer 9

it completes the circuit and carries away the current from the appliance

Question 10

What is the core of each wire made out of?

Answer 10

Copper

Question 11

What is AC and where is it found?

Answer 11

alternating current. The electrons oscillate inside the wire and create a zig-zag on an oscilloscope. Found in mains supply

Question 12

What would happen if you touched the live wire?

Answer 12

you would get an electric shock

Question 13

What is DC and where is it found?

Answer 13

direct current. Electrons move directly along the wire to their destination, creating a straight line on an oscilloscope. Supplied by cells and batteries

Question 14

What is the frequency of the current in the UK Mains supply?

Answer 14

50 Hz

Question 15

Why does a moving charge transfer energy?

Answer 15

The charge does work against the resistance of the circuit.

Question 16

Kettles transfer energy in what way to which store from the mains supply?

Answer 16

Transfer electrically from mains supply, thermal store

Question 17

Handheld fans transfer energy in what way from where to which store?

Answer 17

electrically from battery, kinetic store

Question 18

What does the total energy transferred by an appliance depend on? Give two answers.

Answer 18

Its power (the energy that is transferred per second) and how long it is on for

Question 19

Give the equation linking energy transferred, time and power.

Answer 19

Energy transferred (J)= power (W) x time (s)
E=Pt

Question 20

What does a power rating tell you?

Answer 20

The maximum amount of energy transferred between stores each second

Question 21

An appliance transfers 6000 J of energy in 30 seconds, Calculate its power.

Answer 21

200W

Question 22

Give the equation linking charge flow, voltage, and energy transferred.

Answer 22

Energy transferred (J) = charge flow (C) x potential difference (V)
E = QV

Question 23

An appliance with a higher voltage will supply more energy to the circuit per coulomb of charge. True or False?

Answer 23

True

Question 24

Give the equation linking power, current, and voltage.

Answer 24

Power (W) = Potential difference (V) x Current (A)
P=VI

Question 25

Give the equation linking power, current, and resistance.

Answer 25

P=I^2R

Question 26

Calculate the energy transferred from a 200V source as 10,000C of charge passes.

Answer 26

2,000,000J or 2MJ

Question 27

What two things is the National Grid made up of?

Answer 27

Giant network of **cables** and **transformers** that connects the power stations to the consumers

Question 28

Why do most power stations not work to their full potential?

Answer 28

to leave spare capacity to cope with high demand.

Question 29

What occasions mean that there is a high demand of electricity?

Answer 29

- coming home from work, school - when its dark, cold - popular events : sporting final on TV

Question 30

Why is a high potential difference needed for the electricity being carried through the national grid?

Answer 30

A very high power is required, so it needs either a high voltage or high current. If the current is high, too much energy would be wasted as thermal energy before reaching its destination. It’s a lot cheaper to boost the pd up really high and help the current as low as possible.

Question 31

How high does a step-up transformer take the voltage?

Answer 31

400,000V

Question 32

How does a step up transformer work?

Answer 32

- It has a primary coil and a secondary coil joined with an iron core. - Step up transformers have more turns on the secondary coil than on the primary coil, so the voltage gets increased when it passes through - as the pd is increase by the transformer the current is decreased.

Question 33

What devices bring the voltage back down to a safe level, and what voltage is this?

Answer 33

step down transformers, 230V

Question 34

How does a step down transformer work?

Answer 34

They have more turns on the primary could than on the secondary. - the pd is reduced at the local consumer and the current in increased.

Question 35

How does the power in the primary coil equal the power in the secondary coil?

Answer 35

transformers are nearly 100% efficient

Question 36

What is static electricity?

Answer 36

Charges which are not free to move, e.g. in insulating materials. This causes them to build up on one place and it often ends with a spark or a shock when they finally do move

Question 37

How does static electricity created?

Answer 37

- Ehen insulating materials are subbed together, negatively charged electrons will be scraped off one and dumped on the other - this leave the one material electrically charged with a positive static charge and the other a equal negative static charge

Question 38

Name an example of static electricity between 2 materials

Answer 38

Polythene and acetate rods **Acetate**: - loses electrons - becomes positive Andrew TATE lost followers/ lost electrons **Polythene**: - gains electrons - become negative

Question 39

What happens to the potential difference between the object and the earth when electric charge builds up on a object?

Answer 39

The pd increase . The earth is a 0V

Question 40

What happens if the potential difference gets large enough?

Answer 40

The **electrons can jump across the gap** between the **charged object and the earth** - this is a **spark** - they can also jump to any **earthed conductor** that is nearby - which is why you can get static shocks getting out the car - a charge builds up on the car’s metal frame and when you touch it the **charge travels through you to the earth.**