Chapter 19 - Practical Electricity

Question 1

What is the Symbol for Power

Answer 1

P

Question 2

P = ? (Voltage and Current)

Answer 2

V x I

Question 3

P = ? (Resistance and Current)

Answer 3

I x I x R

Question 4

P = ? (Resistance and Voltage)

Answer 4

V x V / R

Question 5

S.I Unit for Power?

Answer 5

Watt

Question 6

An electrical appliance has a power of 1000W, what does it mean?

Answer 6

That means i convert/use 1000J of electrical energy in one second

Question 7

What is the symbol for energy?

Answer 7

E

Question 8

What is the S.I Unit for energy?

Answer 8

Joule (J)

Question 9

E = ? (Power and Time)

Answer 9

P x t

Question 10

Cost of electrical energy used = ?

Answer 10

Number of kWh used x Cost per kWh, the unit kWh is commonly used to calculate the cost of electricity.

Question 11

What does 1 kWh means?

Answer 11

1000 Watt of power used in 1 hour

Question 12

In a three pin plug, which are the positions of the Live, Neutral and Earth wires?

Answer 12

Earth: Top
Live: Right
Neutral; Left

Question 13

What is the purpose of using a double switch?

Answer 13

To allow the user to control the current flow from two different places, eg. opposite ends of corridor

Question 14

All switches/fuses must be connected to the live wire not the neutral wire. Why?

Answer 14

If the switch/fuse is connect to the neutral wire, when the switch is open/the fuse is melted, the live wire is still connected to the appliance. Thus, current can still flow through appliance, the metal casing of the appliance remain ‘live’, and if people touch the appliance, they will get electrocuted

Question 15

What are the 5 safety features that can be found in our homes which prevent electrical hazards from occurring?

Answer 15

Circuit Breaker
Earthing/Earth Wire
Fuses
Double Insulation
Switches

Question 16

What is purpose of inserting a fuse into an electrical appliance?

Answer 16

To protect the equipment and wires from EXCESSIVE current flow

Question 17

How does a fuse work to prevent excessive current flow?

Answer 17

Fuse has a very low melting point, when it is heated up due to excessive current flow, it will melt immediately and thus cut off the current.

Question 18

If a circuit is designed to take 3A of current, what rating of fuse is suitable for the circuit?

Answer 18

4A or 5A fuse, the rating of the fuse should be just slightly higher than the current that the circuit is designed to take.

Question 19

What is the colors of the earth, live and neutral wire respectively?

Answer 19

Earth:Green and yellow
Live: Brown
Neutral: Blue

Question 20

How does the Miniature Circuit Breaker works to prevent electrical hazard?

Answer 20

When there is a short circuit or excessive current flow, the Miniature Circuit Breaker will ‘trip’ and cut off the electricity.

Question 21

What is the advantage of Miniature Circuit Breaker over fuse?

Answer 21

Miniature Circuit Breaker can be reset to regain the electricity supply, however, a when a fuse is blown, it has to be replaced by another one.

Question 22

Why an Earth wire is necessary for an electrical appliance?

Answer 22

Because sometimes the live wire might come loose and touch the metal casing of the appliance, and if we touch the metal casing, we will be electrocuted. If earth wire is installed, the current will be diverted to the earth instead and we will be safe to touch the metal casing.

Question 23

The earth wire must always be connected to ?

Answer 23

The metal casing of the electrical appliance

Question 24

What is symbol for double insulation?

Answer 24

回

Question 25

What is the safety feature of the double insulation?

Answer 25

It offer double level of insulation. A insulation covering the live wire and the neutral wire. A outer casing complete made of plastic (non-conductor of electricity)

Question 26

How does a electric shock happen?

Answer 26

The insulation of the wires may worn off over time. When the wires are exposed and the person touch the wire, the current will flow through the human body, thus the person will get a electric shock

Question 27

How does a fire caused by wires happened at home?

Answer 27

The insulation of the wires may worn off over time. The live and neutral wire may touch each other and thus there will a short circuit which allows large current flow. A fire will happen due to overheating of wire or the plastic insulation

Question 28

Why cables will get overheated?

Answer 28

Cables have their own current rating. Sometimes sockets are overloaded using extension plugs. When the current flowing exceeds the current rating, the overloaded cable will get overheated.

Question 29

Why a DRY body touch a live wire will not get electrocuted?

Answer 29

The SKIN of the dry body has a very high resistance

Question 30

What is the logic behind a test pen that allows the electrician to test the wire and identify if the wire is neutral or live wire without harming himself?

Answer 30

A test pen contain a high-resistance carbon conductor which allows small and harmless current to pass through the test pen and the human body from the live wire to the earth. When the current pass through, neon tube will light up to notify the electrician that the wire is a live wire.

Question 31

What are three example and two examples for renewable and non-renewable source of energy respectively?

Answer 31

Renewable: Solar, wind and hydroelectric | Non-renewable: Fossil Fuel, Nuclear

Question 32

What are the environmental impacts for solar, hydroelectric, wind, nuclear and fossil fuel energy?

Answer 32

Solar: Large area needed to be clear for solar panels Hydroelectric: Construction of dams will disrupt ecosystem Wind: turbines produce noise pollution and require large open areas Fossil Fuel:Burning of fuel results in air pollution Nuclear:Wastes from uranium mining will contaminate groundwater and surface water