Physics Work & Energy DUHS 2022
PMDC Verified Question 56 of 108
One kilowatt hour is equal to:
A
\( 36 \times 10^4 \text{ J} \)
B
\( 36 \times 10^6 \text{ J} \)
C
\( 3.6 \times 10^5 \text{ J} \)
D
\( 3.6 \times 10^6 \text{ J} \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: \( 3.6 \times 10^6 \text{ J} \)
Concept:

Convert the commercial unit of energy into the SI unit (Joules) by converting both prefixes and time units.

Formula:

$$ 1 \text{ kWh} = 1 \text{ kW} \times 1 \text{ hour} $$

Solution:

  • 1 kilowatt = 1000 Watts (Joules/sec).


  • 1 hour = 3600 seconds.


  • Multiply them: \( 1000 \text{ J/s} \times 3600 \text{ s} = 3,600,000 \text{ Joules} \).


  • In scientific notation: \( 3.6 \times 10^6 \text{ J} \).


Why other options are incorrect:

Mismatched exponents: \( 3.6 \times 10^5 \) misses a zero (only 10 minutes instead of 60). \( 36 \times 10^6 \) is 10 times too large.

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