An electric heater takes 4A when operated on a 250V supply. What is the cost of the electricity consumed at 10k per kWh when the heater is used for 5 hours?

Analyze the question: We need the electrical energy used by the heater in kWh, then multiply by the cost per kWh.

Concept:

• Power: P = IV
• Energy (kWh) = Power (kW) × time (hours)
• Cost = Energy × cost per kWh

Solution:

1. Power: P = IV = 4 × 250 = 1000 W = 1 kW
2. Energy: E = 1 kW × 5 h = 5 kWh
3. Cost: 5 kWh × 10k per kWh = 50k

Answer: B (50k)

Tip: Always convert watts to kilowatts before multiplying by hours. Here 1000 W is exactly 1 kW, which makes the calculation easy. Also watch the units, because 50k (kobo) is not the same as N50. 100k = N1.