A bulb of 100 W glows for 6 hours a day. The units of energy consumed in 7 days would be:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 4.2 units
Electrical energy used by an appliance is power multiplied by time, and the commercial unit of electrical energy is the kilowatt hour: 1 unit = 1 kWh.
\( P = 100\,\mathrm{W} = 0.1\,\mathrm{kW} \)
\( t = 6\,\mathrm{h} \times 7 = 42\,\mathrm{h} \)
\( E = P\,t = 0.1\,\mathrm{kW} \times 42\,\mathrm{h} = 4.2\,\mathrm{kWh} \)
So the bulb uses 4.2 units.