Power MCQs

Q1. Which uses MORE electrical energy: a 100 W bulb for 2 hours or a 40 W bulb for 5 hours?

• A.the 100 W bulb (200 Wh vs 200 Wh - they are equal)
• B.the 40 W bulb, clearly more
• C.the 100 W bulb, clearly more
• D.impossible to compare

Answer: A. the 100 W bulb (200 Wh vs 200 Wh - they are equal)

Q2. Why is the kilowatt-hour, not the joule, used on household electricity bills?

• A.the joule is too small a unit for the large energy used by homes
• B.the joule is too large for household energy
• C.kilowatt-hour measures power, not energy
• D.joules cannot measure electrical energy

Answer: A. the joule is too small a unit for the large energy used by homes

Which principle settles this? Household energy is huge in joules, so the larger kWh unit is more practical. Does that line up with one of the options? Yes - Correct. And the rest? option B) 'the joule is too large for household energy' is wrong because The joule is very small; homes use millions of joules, so kWh is convenient; option C) 'kilowatt-hour measures power, not energy' is wrong because The kilowatt-hour is a unit of energy. Pick: A) the joule is too small a unit for the large energy used by homes.

Q3. Which statement correctly relates work, power and time?

• A.work = power x time
• B.power = work x time
• C.time = power x work
• D.work = power / time

Answer: A. work = power x time

What does the chapter say about this? From power = work/time, work = power x time. Does that line up with one of the options? Yes - Correct. And the rest? option B) 'power = work x time' doesn't hold - Power = work / time, not work x time; option C) 'time = power x work' is wrong because Time = work / power, not power x work. Pick: A) work = power x time.