Chapter 19 - Practical Electricity

Which of the following appliances makes use of the heating effect of electricity?

• Electric escalator

• Electric fan

• Electric rice cooker

• Fluorescent lamp

Which of the following is a unit of energy?

• Coulomb per second

• Newton per metre

• Volt per coulomb

• Watt second

A 50 Ω resistor is connected in series with a 9.0 V battery. What is the power loss in the resistor?

• 0.45 W

• 0.62 W

• 1.6 W

• 5.6 W

A 24 V electric motor is used to lift a load of 100 N through a height of 5 m in 12 s. Assuming that the motor is 100% efficient, what is the average current in the motor?

• 1.74 A

• 3.23 A

• 20.1 A

• 250 A

The cost of electricity is 27 cents per kWh. What is the cost of using a 1000–1200 W iron at maximum power for 45 minutes?

• 12.2 cents

• 14.6 cents

• 24.3 cents

• 1458 cents

A fuse blows when a light is switched on in a house. The house owner replaces the fuse, but the second fuse also fails. The house owner then uses a third fuse with a higher rating. Why is this not recommended?

• Using a fuse with too high a rating will cause electric shocks.

• Fuses allow the circuit to work only if the rating is exactly right.

• Using a fuse with a higher rating might allow the circuit to work, but the fault is not corrected.

• The fuse with a higher rating will definitely not work, as it allows a smaller current to pass through it before melting.   

The power rating and the duration of usage of four electrical appliances are summarised in the table.

Which appliance consumes the most energy?

• Fan

• Lamp

• Rice cooker

• Washing machine

The diagram shows an electrical appliance with a metal casing (indicated by the dotted line) connected to the power supply. Where should a switch be placed?

• A

• B

• C

• D

A student draws a circuit, shown below, to show how an appliance should be connected to a fuse and the household mains.

Identify the error in the circuit.

• The fuse rating is too high.

• The fuse rating is too low.

• The fuse is connected wrongly.

• The switch is connected wrongly.   

Which of the following conditions is not considered a hazard to the user?

• Overloading of appliances in one socket.

• Exposed wires due to damaged insulation.

• Handling electrical appliances in damp conditions.

• Connecting the earth wire to the casing of the appliance.