Practical Electricity

Question 1

Electrical heating

Answer 1

Heating element is made out of nichrome coiled around an insulating fire proof material, which has high resistivity, high melting point and is able to withstand high temperature without being easily oxidised.

Question 2

Electrical lighting

Answer 2

Wire filament which is heated to high temperature by passing an electric current through it. Inert gas is present to prevent oxidation at the filament

Question 3

Power

Answer 3

P=IV
P=I^2R
P=V^2/R
P=E/t

Question 4

Energy

Answer 4

E=VIt
E=I^2Rt
E=(V^2/R)t

Question 5

Kilowatt-hour,kWh

Answer 5

Amount of energy used by a 1kW appliance in 1 hour.

1kWh = 3.60 x 10^6 J

Question 6

Electrical hazards

Answer 6

Damaged insulation
Overheating of cable
Damp conditions

Question 7

Live wire

Answer 7

Wire with high voltage

Question 8

Neutral wire

Answer 8

Wire with low or zero voltage

Question 9

Damaged insulation

Answer 9

When the live wire is in direct contact with the neutral wire, a short circuit which causes a large current to flow through the wire will produce enough heat to cause a fire

Question 10

Overheating of cables

Answer 10

Overly large electrical current flowing through the conducting wires due to short circuit or overloading, which is caused by plugging too many appliances into the same power outlet, resulting in an excessively large current being drawn.

Question 11

Damp conditions

Answer 11

Water provides a conducting path for a large current to flow from a live wire to a person

Question 12

Circuit breakers

Answer 12

They are connected to the live wires, and switches off the electrical supply to a circuit when large current flows through them to prevent current surges

Question 13

Fuses

Answer 13

Connected to the live wire, it melts when the current through it is larger than its rated value, breaking the circuit

Question 14

3 pin plug- live wire

Answer 14

Brown

Question 15

3-pin plug- neutral wire

Answer 15

Blue

Question 16

3 pin plug- earth wire

Answer 16

Yellow and green.
It is a wire with low resistance connected to the metal casing of appliances. The metal casing may become live if the live wire touches it which will cause the user to be electrocuted if there is no earth wire connected to the casing when the user is in contact with the metal casing. The large current will not flow through the user but to the ground through the low resistance earth wire

Question 17

Double insulation

Answer 17

Insulated electric cables and non-metal external casing