An incandescent electric bulb converts 20% of its power consumption into light, and the remaining power is dissipated as heat. The bulb's filament has a resistance of 200~\Omega and 2 A current flows through it. If the bulb remains ON for 10 h and the rate of electricity charge is ₹5/unit, then which among the following is the correct amount for the money spent on producing light?
- A. ₹5
- B. ₹6
- C. ₹7
- D. ₹8 ✓
Correct Answer: D. ₹8
Explanation
Total power P = I^2 R = (2)^2 \times 200 = 800~W = 0.8~kW. Energy in 10h = 0.8 \times 10 = 8~kWh (units). Total cost = 8 \times 5 = ₹40. Cost for light (20%) = 0.20 \times 40 = ₹8.
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