2 Mains electricity

Question 1

What is an insulator?

Answer 1

A material through which it is very difficult or impossible for electricity to flow.

Question 2

What is a conductor?

Answer 2

A material that allows electricity to flow through it easily.

Question 3

What is a fuse?

Answer 3

The fuse is usually in the form of a cylinder or cartridge, which contains a thin piece of wire made from a metal that has a low melting point.

Question 4

What is the circuit symbol for a fuse?

Question 5

What happens if the current is too large in the circuit?

Answer 5

If there is too large a current in the circuit then the fuse wire becomes very hot and melts.

Question 6

How does the fuse ‘blowing’ protect you?

Answer 6

Because the fuse has melted so the circuit is now incomplete, which prevents you from getting a shock and reduces the possibility of an electrical fire.

Question 7

What must happen to the blown fuse?

Answer 7

It must be replaced with a new one of the same size before the appliance can be used again.

Question 8

What is the correct fuse for a circuit?

Answer 8

The correct fuse for a circuit is the one that allows the correct current but blows if the current is a little larger.

Question 9

What is the correct fuse if the current in a circuit is 2A?

Answer 9

3A

Question 10

What is a circuit breaker?

Answer 10

Modern safety devices, such as those you might find in your consumer unit, are often in the form of trip switches or circuit breakers.

Question 11

What happens if too large of a current flows into the circuit breaker?

Answer 11

A switch automatically opens making the circuit incomplete, so stopping any current from passing.

Question 12

How does the switch then go back to normal after the fault in the circuit has been corrected?

Answer 12

The switch is reset, usually by pressing a reset button.

Question 13

What happens to the switch or circuit breaker after the switch has been reset?

Answer 13

There is no need for the switch or circuit breaker to be replaced, as there is when fuses are used.

Question 14

What should the earth wire be connected to?

Answer 14

To the appliances which have a metal casing.

Question 15

What is an earth wire?

Answer 15

It is a copper wire coated in striped plastic that provides a path for current to flow from the case of the device to the ground

Question 16

How does an earth wire protect the user?

Answer 16

If the live wire becomes damaged or breaks and comes into contact with the casing, the earth wire provides a low-resistance path for the current.

Question 17

What would happen without the usage of an earth wire?

Answer 17

Anyone who touches the casing of the faulty appliance would receive a severe electric shock as the current passed through them to earth.

Question 18

What is double insulation?

Answer 18

It is when some modern appliances now use casings made from an insulator such as plastic rather from metal. The user cannot touch the electrical parts since they are insulated in this way.

Question 19

What kind of wire do appliances use that have double insulation?

Answer 19

They use a two-wire flex.

Question 20

What is a flex?

Answer 20

It is a wire.

Question 21

Do doubly-insulated appliances need an earth wire?

Answer 21

No this is because the double-insulation protects the user of the appliance from an electrical shock by preventing any possibility of the external casing becoming live (the live wire can not touch the casing even if wires inside become loose), thus eliminating the need for an earth connection.

Question 22

Where should switches in main circuits be placed?

Answer 22

In the live wire so that when the switch is open no electrical energy can reach an appliance.

Question 23

What happens if the switch is placed in the neutral wire?

Answer 23

Electrical energy can still enter a faulty appliance, and could possibly cause an electric shock.

Question 24

How is the wiring in a house designed?

Answer 24

The wiring in a house is designed to let current pass through it easily.

Question 25

What result does the fact that the current can pass through easily have on the temperature?

Answer 25

The wires do not become warm when appliances are being used.

Question 26

What kind of resistance do these wires have?

Answer 26

Low resistance.

Question 27

Why would we want wires or heating elements to become warm?

Answer 27

For certain appliances like kettles or toasters.

Question 28

What are heating elements?

Answer 28

Coils of wires used to transfer electrical energy and heat energy.

Question 29

How are the wires of a heating element designes?

Answer 29

They are designed to have a high resistance so that that as the current passes through them energy is transferred and the elements heat up.

Question 30

What are other common appliances that make use of the heating effects of electricity?

Answer 30

• Kettles.
• Dishwashers.
• Electric cookers.
• Washing machines
• Electric fires
• Hairdryers

Question 31

What does high reisistance mean?

Answer 31

That its harder for currents to pass through. Therefore, making the heating elements warm up.

Question 32

What is a halogen lightbulb?

Answer 32

A lightbulb that contains a small amount of halogen such as iodine or bromine.

Question 33

What is the equation for Power?

Answer 33

P (power) = I (current) x V (voltage)

Question 34

What is equation for energy transferred?

Answer 34

E (energy transferred) = I (current) x V (voltage) x T (time)

Question 35

What is an alternating current or alternating voltage?

Answer 35

A voltage that is continuously changing in value and direction.

Question 36

What is an alternating voltage or current different to?

Answer 36

The currents and voltages that we get from cells.

Question 37

What is direct current or direct voltage?

Answer 37

Cells and batteries provide these currents and voltages. They are always in the same direction and have the same value.

Question 38

What is a graph that shows the relationship between voltage and how ac and dc supplies act?