P2.5

Question 1

Why do we use alternating current when switching a light on?

Answer 1

Because mains electricity is an ac supply.

Question 2

What does an alternating current do?

Answer 2

Repeatedly reverses its direction.

Question 3

What is a direct current? And why is it called this?

Answer 3

The current in the circuit.

Because it is in one direction only.

Question 4

What two types of wire does every main circuit have?

Answer 4

• live wire

- neutral wire

Question 5

Why does the current through a mains appliance alternate?

Answer 5

Because the mains supply provides an alternating potential difference between the two wires.

Question 6

What is the potential difference between the live wire and earth referred to?

Answer 6

Voltage of the live wire.

Question 7

Why is the live wire dangerous?

Answer 7

Because its voltage repeatedly changes from + to - and back every cycle.

Question 8

What do we use a oscilloscope for?

Answer 8

To measure the peak potential difference and the frequency of a low voltage ac supply.

Question 9

What does the Y-gain control tell us?

Answer 9

That each centimetre of height is due to a potential difference.

Question 10

What happens when you plug in a heater with a metal case into a wall socket?

Answer 10

You Earth the metal case automatically.

Question 11

Why are the outer casings of plugs etc of all mains circuits and appliances made of hard-wearing electrical insulators?

Answer 11

Because plugs etc contain live wires.

Question 12

What are sockets made of?

Answer 12

Stiff plastic materials with the wires inside.

Question 13

What do mains cables consist of?

Answer 13

Two or three insulated copper wires surrounded by an outer layer of flexible plastic material.

Question 14

What is the colour of a live wire, neutral wire and Earth wire?

Answer 14

Live-brown
Neutral-blue
Earth-green and yellow

Question 15

What do we use a fuse for?

Answer 15

For a mains appliance.

Question 16

Why is a fuse always on the live side of an appliance?

Answer 16

Because if the fuse blows the appliance is then cut off from the live wire.

Question 17

What is a circuit breaker?

Answer 17

An electromagnet switch that opens when there is a fault.

Question 18

What do people use instead of fuses? Why?

Answer 18

Circuit breakers because they work faster and can be reset more quickly.

Question 19

What is the RCCB?

Answer 19

Residual Current Circuit Breaker.

Question 20

What does the RCCB do?

Answer 20

Cuts off the current in the live wire when it’s different from the current in the neutral wire.

Question 21

What happens when the live wire inside an appliance touches a neutral wire? What is this called?

Answer 21

A very large current passes between the two wires at the point of contact.
Called a short circuit.

Question 22

What happens when the fuse blows?

Answer 22

It cuts the current off.

Question 23

What is the power of the appliance?

Answer 23

Energy it transfers.

Question 24

What is the equation for power?

Answer 24

=energy transferred/time

Question 25

What is the equation for the power supplied?

Answer 25

=current X potential difference

Question 26

What is the current for an electrical appliance?

Answer 26

The charge that flows through it each second.

Question 27

What is the potential difference in an electrical appliance?

Answer 27

Energy transferred to it each second.

Question 28

What is the equation for charge?

Answer 28

=current X time

Question 29

What happens when an electrical appliance is on?

Answer 29

I lectins are forced through the appliance by the potential differenc of the power supply unit.

Question 30

What is coulomb?

Answer 30

Amount of charge flowing through a wire or a component.

Question 31

What do the electrons collide with? Why?

Answer 31

Vibrating metal ions of the resistor to transfer energy to them.

Question 32

What happens when the ions of the resistor gain kinetic energy?

Answer 32

They vibrate even more and resistor becomes hotter.

Question 33

What does the energy transferred in a certain time in a resistor depend on?

Answer 33

• the amount of charge that passes through it

- the potential difference across the resistor

Question 34

Why are electrical faults dangerous?

Answer 34

It could give someone a nasty shock or even electrocute them resulting in death.

Question 35

Why can electrical faults cause fires?

Answer 35

Too much current passes through a wire or an appliance and heats it up.

Question 36

Name two types of low energy bulbs:

Answer 36

• low energy compact fluorescent bulb

- low energy light emitting diodes