4.4 Practical Electricity

What is a possible material for the heating element in an electric iron?

• copper

• steel

• nichrome

• stainless steel

Answer explanation

Nichrome has a high resistance thus produces more heat. It does not oxidise easily and has a high melting point so does not melt easily.

Why is the filament in a light bulb made from tungsten?

• Tungsten has melting point higher than 3000 degree celcius

• Tungsten has high resistance to allow high current to pass through

• Tungsten has high mass so that more heat can be stored in the filament

• Tungsten has high specific heat capacity so that small amount of heat can increase the temperature to a large extent

What is the current flowing through an appliance marked '240 V, 40 W'?

• 0.17 A

• 3.00 A

• 6.67 A

• 6.00 A

What is the power produced by an appliance marked '240 V, 2 A'?

• 8.3 mW

• 60 W

• 120 W

• 480 W

What is the power dissipated by the lamp in the diagram?

• 2 W

• 3 W

• 6 W

• 18 W

The lamp is switched on for 5 minutes.

How much energy has been dissipated from the lamp?

• 120 J

• 480 J

• 600 J

• 36 000 J

What is 1 kWh?

• 1000 J of energy

• 1000 W of power

• Energy used by 1 kW device in 1 hour

• $1 worth of energy

How much energy does a spot light rated 2 kW consume in 6 h?

• 3 kWh

• 4 kWh

• 8 kWh

• 12 kWh

How much energy does a lamp rated at 40 W consume in 30 min?

• 0.02 kWh

• 1.2 kWh

• 20 kWh

• 1200 kWh

If 1 kWh of electricity cost $0.20, how much does it cost to switch on a spot light rated at 2 kW for 6 h?

• $0.60

• $2.40

• $15.00

• $60.00