UPSC NDA 2 2016 General Ability Solved Paper

Concept:Electrical energy is the product of electric power and time.The kilowatt-hour (kWh) is a commercial unit of energy, while the joule (J) is the SI unit.Explanation:Step 1: Recall that $1$ kWh is the energy used by a $1$ kW device running for $1$ hour.Step 2: Convert power: $1$ kW $= 10^3$ W.Step 3: Convert time: $1$ hour $= 3600$ seconds.Step 4: Since $1$ W $= 1$ J/s, the energy in joules is $E = P \times t = (10^3 \text{ W}) \times (3600 \text{ s}) = 3.6 \times 10^6$ J.Step 5: Write $3.6 \times 10^6$ as $36 \times 10^5$: $3.6 \times 10^6 = 36 \times 10^5$.Thus, $1$ kWh $= 36 \times 10^5$ joules.Answer:$36 \times 10^5$ joules (Option B).