P2.4 - Mains Electricity

Question 0

What is alternating current?

Answer 0

Current that repeatedly reverses its direction.

Question 1

What is direct current?

Answer 1

Current in one direction.

Question 2

What is the peak voltage of an alternating pd?

Answer 2

The maximum voltage measured from zero.

Question 3

How is the frequency of an alternating current calculated with an ocilloscope?

Answer 3

Freq. = 1 / time taken for one cycle

Question 4

What is the casing of mains electricity devices made of and why?

Answer 4

Stiff, thermosetting plastic because it is a good insulator.

Question 5

What is in a mains cable?

Answer 5

Three insulated copper wires surrounded by a plastic outer sleeve.

Question 6

What colour is the live wire?

Answer 6

Brown

Question 7

What colour is the neutral wire?

Answer 7

Blue

Question 8

What colour is the earth wire?

Answer 8

Yellow and green

Question 9

Why does a three pin plug have an earth pin?

Answer 9

So the metal case of a mains appliance is insulated.

Question 10

What are plug pins made of?

Answer 10

Brass because it is a good conductor and doesn’t rust.

Question 11

What is a fuse used for?

Answer 11

The appliance is cut off if the current is too high.

Question 12

Why is a fuse in between the live wire and pin?

Answer 12

The appliance can be cut off from the current if the fuse blows?

Question 13

What is a circuit breaker?

Answer 13

An electromagnetic switch that trips in the event of too much current passing through.

Question 14

Why aren’t appliances with plastic cases earthed?

Answer 14

Plastic is an insulator so cannot become live.

Question 15

How does a fuse work?

Answer 15

A fuse contains a thin wire that heats up and melts if too much current passes through.

Question 16

What is the rating of a fuse?

Answer 16

The maximum current that can pass through without melting the wire.

Question 17

Give three advantages of using an RCCB.

Answer 17

• It works faster than a circuit breaker
• It can be used where there is no earth
• It is more sensitive.

Question 18

How does an RCCB work?

Answer 18

An RCCB trips when the current in the live wire is different to the current on the neutral wire.

Question 19

What is the relationship between power and energy?

Answer 19

The power supplied to a device is the energy transferred each second.

Question 20

What is the equation for power of an appliance?

Answer 20

Power (W) = energy transferred (J) / time (s)

Question 21

What is an electrical current?

Answer 21

The rate of flow of charge.

Question 22

How is the flow of electric charge calculated by the current?

Answer 22

Charge (Coulombs) = current (amps) x time (seconds)

Question 23

What energy transfers take place when charge flows through a resistor?

Answer 23

The energy transferred makes the resistor hot.

Question 24

How is energy transfer calculated in relation to pd and charge?

Answer 24

Energy transferred (J) = pd (V) x charge flow (C)

Question 25

What is the relationship between the electrical energy supplied by the battery and energy transferred to the components?

Answer 25

After a while, the energy supplied is equal to the energy transferred.

Question 26

Why are electrical faults dangerous?

Answer 26

They can cause electric shocks and fires.

Question 27

Give three important factors to consider when buying an electrical appliance.

Answer 27

• Cost
• Power rating
• Efficiency rating

Question 28

What is the most efficient type of lightbulb?

Answer 28

Led

Question 29

What is the lifetime of an LED?

Answer 29

30,000 hours

Question 30

What is the most inefficient lightbulb?

Answer 30

Filament bulb