Q. An iron box of 400 W power is used daily for 30 minutes. If the cost per unit is 75 paise, find the weekly expense on using the iron box.
Energy obsessive in 30 minutes = Power × time in hours
= 400 × ½ = 200 W h
Energy consumed in one week = 200 × 7 = 1400 Wh = 1.4 unit
Cost / week = Total units consumed × rate/ unit
= 1.4 × 0.75 = Rs.1.05