Two bulbs of 40W each are lighted for eight hours daily. Find the cost of electrical energy consumed by them in one week at Rs. 3 per unit.
Given
Power = 40W
Time = 8 hours
Now
Power =
⇒
⇒ Energy =
Energy consumed by 2 bulbs in 1 week = 320×2×7 = 4480 Wh = 4.48 kW
(∵ 1kWh = 1000Wh)
Total units = 4.48 units
Now
Cost of 1 unit = Rs 3
Total cost = 4.48 ×3 = Rs13.44
Total cost for 1 week is Rs 13.44