NumericalModerate1 mark
9(i)
Calculate: An electric iron rated 1100 W, 220 V is operated for 5 hours.
the energy consumed in kWh.
Topic: Electrical energy in kWh
Question wording verified against source paper
Answer
Exam answer
Given: P = 1 100 W = 1.1 kW, time t = 5 hours
Energy = power (in kW) × time (in hours) = 1.1 × 5 = 5.5 kWh
Energy consumed = 5.5 kWh (5.5 units)
Explanation
Convert the watts to KILOwatts before multiplying, because the answer is wanted in kilowatt-hours. Using 1 100 × 5 gives 5 500, which is watt-hours, not kWh — out by a factor of a thousand.
Keep the time in hours too. The kilowatt-hour is deliberately a mixed unit: kilowatts times hours, nothing converted to seconds. One kWh is what the electricity board calls a "unit".
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