15. Practical Electricity

Question 1

What is the formula to measure Voltage?

Answer 1

1. Work done/ charge
2. work done/ time x current

Question 2

What is the formula to calculate power?

Answer 2

Power= Voltage x Current
Where the SI unit of power is watts

Question 3

How to conserve energy and reduce carbon footprints?

Answer 3

1. Reduce usage of appliances with higher electricity consumption
2. Choose appliances with lower electricity consumption

Question 4

Hazardous situation: damaged insulation

Answer 4

1. Wires are usually covered with insulating materials to prevent electric shocks. However, high electric field and temperature can lead the cover to be old and expose people to the wire

Question 5

Hazardous situation: Overheating of cables

Answer 5

1. Is caused by rising temperatures in an electrical circuit. Usually, it is caused by large amount of current, too many plugs connected to a socket or poor contact between the plug and socket.

Question 6

Hazardous situation: Damp environment

Answer 6

1. As water usually contain charged ions and impurities that make it a good conductor of electricity

Question 7

Safety Feature: Fuse

Answer 7

• It is added to an electric circuit to prevent excessive current flow
• The fusible wire will melt when the current flowing through exceeds a certain value

Question 8

Safety Feature: Circuit Breaker

Answer 8

• They also prevent excessive current from flowing through
  -Unlike a fuse they are not added to the plug but part of the main electrical wiring to an apartment

Question 9

Safety Feature: Earthing the metal casing

Answer 9

• If outer casing made of metal equals to an extra electrical protection
• It encloses the electrical part parts of an appliances and is connected to the earth, keeping the user safe
• The live wire passes through the earth metal casing flows to the ground

Question 10

Safety Feature: Double Insulation

Answer 10

• Appliances are enclosed in a plastic casing which is not earthed
• Has two layers of insulation to enclose all exposed surfaces

Question 11

Safety Feature: Wiring in a mains plug

Answer 11

• Live wire which is usually brown carries the high voltage and the current
• Earth wire is yellow and green which is a safety wire that is needed to earth appliances with a metal casing
• Neutral wire is usually blue and is kept at zero voltage

Question 12

Summary of safety features: (Hint: There is 5 safety features)

Answer 12

1. Fuses: used in socket plugs to prevent excessive current
2. Circuit breaker: Used in distribution box to prevent excessive current
3. Earthed metal casing: To prevent live wire from causing metal casing to be at a high electrical potential
4. Double Insulation: To prevent contact with live wire
5. Earth wire: To earth the metal casing of appliance