alleryA lamp rated 100 W at 200 V runs at 100 V for 5 h. Assume constant resistance. At ₹8 per kWh, what does it cost?
A₹8
B₹1
C₹4
D₹2
Answer & Solution
Correct answer: B. ₹1
Its resistance is 400 Ω, so at 100 V it uses 25 W, consuming 0.125 kWh in 5 h and costing ₹1.
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