Power in homes (kWh)

Which of the following shows the unit for energy?

• Ampere (A) and Coulomb (C)

• Joule (J) and Volt (V)

• Joule (J) and kilowatt hour (kWh)

• ohm( Ω) and Volt (V)

A household uses 430 kW h of electricity. Electricity cost $0.20 per kW h. Calculate the cost of electricity for the household.

Answer explanation

Cost = 430 x $0.20

= $8.60

A circuit is set up with electrical components X, Y and Z as shown.

• X: battery

  Y: fixed resistor
  Z: bell

• X: battery

  Y: variable resistor
  Z: lamp

• X: cell
  Y: fixed resistor
  Z: bell

• X: cell
  Y: variable resistor
  Z: lamp

Two different lamps, L1 and L2, are connected in a circuit.
A multimeter is used to measure the voltage across lamp L1.

At which points in the circuit should the probes of the multimeter be connected to obtain the voltage across L1?

• Probe 1: P

  Probe 2: R

• Probe 1: Q

  Probe 2: R

• Probe 1: R

  Probe 2: P

• Probe 1: R

  Probe 2: Q

A 12 V battery is connected to two different resistors R1 and R2.

The reading on the voltmeter is 4 V. What is the voltage across resistor R1?

• 4 V

• 8 V

• 12 V

• 16 V

Answer explanation

Voltage across R1 = 12 V - 4 V

= 8 V

J, K and L show different arrangements of identical fixed resistors.

Which option puts the arrangements in order of their effective resistance, from the lowest to the highest?

• J, K, L

• J, L, K

• K, J, L

• L, J, K

Four lamps were connected in a circuit.

Which lamp, when blown will result in the other three lamps not lighting up?

• A

• B

• C

• D

A resistor in a circuit has a current of 3 A passing through it and a voltage of 6 V across it.

What is the power of the resistor?

• 2 J

• 2 W

• 18 J

• 18 W

Answer explanation

P = I x V

P = 3 A x 6 V

p = 18 W

The image below shows the information label of an electrical fan.

What is the current for the electric fan to function properly?

• 0.26 A

• 2.30 A

• 3.83 A

• 6.00 A

Answer explanation

I = P / V

I = 60 W / 230 V

I = 0.26 A

The image below shows the information label of an electrical fan.

Electricity cost $0.20 per kW h.

Which row shows the correct calculation to determine the cost of using the electric fan for 3 hours?

Answer explanation

I = P / V

I = 60 W / 230 V

I = 0.26 A