MCQ practice · SSC Physics Board questions · Chapter 11: Current Electricity
How much electric energy will a 60 W bulb use if it is lit for 1 hour every day for 30 days?
Think it through first, then pick an option.
- a 1.8 kW h
- b 30 kW h
- c 60 kW h
- d 1800 kW h
Answer and explanation
Correct answer: a 1.8 kW h
Energy = 60 × 30 ÷ 1000 = 1.8 kWh.
Why the other options are wrong
- b 30 kW h: 30 kWh comes from taking the number of days as the energy; 60 W × 30 h = 1800 Wh = 1.8 kWh.
- c 60 kW h: 60 kWh comes from taking the watts as kWh; one must divide by 1000, giving 1.8 kWh.
- d 1800 kW h: 1800 kWh comes from calling Wh kWh; 1800 Wh = 1.8 kWh.
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