Mains Electricity

Question 1

What is direct current?

Answer 1

• Current flows from positive to negative in one direction.

Question 2

Give a source of direct current.

Answer 2

• Cell.

Question 3

Can direct current have a negative voltage/ current?

Answer 3

• Yes.
• Must stay negative though.

Question 4

What is alternating current?

Answer 4

• Current changes direction

Question 5

Give an alternating current source.

Answer 5

• Mains Electricity.

Question 6

How do we calculate the voltage of a power supply using AC graph?

Answer 6

• Read off peak voltage.

Question 7

What is meant by frequency?

Answer 7

• Frequency is how many cycles an electron completes each second.

Question 8

What is the voltage of mains electricity?

Answer 8

• 230V

For every coloumb of charge, it transfers 230J

Question 9

How many times does the current change direction in the mains supply each second ?

Answer 9

• 50
• 50Hz = frequency

Question 10

What 3 wires is a 3- pin plug made up of?

Answer 10

• Live wire: brown
• Neutral Wire: blue
• Earth Wire: Green

Question 11

What is the live wire?

Answer 11

• Part that carries current to device
• Has voltage of 230V.

Question 12

What is the Earth wire?

Answer 12

• Safety
• Connected to outer casing of device
• If device becomes live from high current/ live wire is near device, carries current to ground.
• Directs current away from device

Question 13

What does the Earth wire avoid?

Answer 13

• Avoids electric shocks.

Question 14

What does the neutral wire do?

Answer 14

• Completes the circuit.
• Has no voltage.

Question 15

What are the actual wires made of?
Why?

Answer 15

• Copper
• Good condudctors

Question 16

Describe what is meant by double insulation.

Answer 16

• Electric components are coated in plastic and covered by plastic casing.

Question 17

Do double insulated devices need an Earth wire?

Answer 17

• No.
• Because the outer casing CAN’T become live (insulated)
• (Electrical components covered and outer case isn’t metal.)

Question 18

What does the fuse protect?

Answer 18

• The fuse protects the device.

Question 19

How do I work out frequency?

Answer 19

1/ time period
time period of one wave = from trough to trough// peak to peak.

Question 20

What is meant by direct potential difference?

Answer 20

• Potential difference is in once direction.

Question 21

What is meant by alternating potential difference?

Answer 21

• Potential difference is changing direction.

Question 22

What are the dangers of providing connection between live wire and the earth?

Answer 22

• You will be earthed
• You will recieve electric shock.

Question 23

What is the potential difference between The Earth and the live wire?

Answer 23

• Live wire = 230V
• Earth wire = 0V
• Difference = 230V

Question 24

What is the potential difference of the neutral wire?

Answer 24

• The neutral wire is at, or close to, earth potential (0V)

Question 25

What is the potential difference of The Earth Wire?

Answer 25

• 0V
• It only carries a current if there is a fault.

Question 26

True or False

If the switch in mains electricity is closed, can a live wire still be dangerous.

Answer 26

• Yes. Live wire can still be dangerous if switch is closed.