alleryOne unit of electrical energy on a domestic bill equals 1 kWh. Expressed in joules, 1 kWh is equal to:
A3.6 × 10⁶ J
B3.6 × 10³ J
C1 × 10³ J
D3600 J
Answer & Solution
Correct answer: A. 3.6 × 10⁶ J
1. By definition $1\ \text{kWh} = 1000\ \text{W} \times 3600\ \text{s}$.
2. Multiply: $1000 \times 3600 = 3.6 \times 10^6$.
3. Since $1\ \text{W}\cdot\text{s} = 1$ J, $1\ \text{kWh} = 3.6 \times 10^6$ J.
4. The option 3600 J is just $1\ \text{W} \times 3600\ \text{s}$, missing the factor of 1000 watts, so it is wrong.
_Source: Balbharati (Maharashtra Board) Class 10 Science & Technology, Ch 4 "Effects of Electric Current", p.58_
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