Question

1) How many kilowatt hours are used by a 3 kW device in 5 hours.
2) What is the cost of using a 2 kW geyser for 4 hours.

Answer 1

1. KwH gives the unit as to much power is consumed by the device in a given amount of time.
Kilowatt hours = Power (in kW)$\times$time (in hours)
= 3$\times$5 = 15 kWh

2. Units consumed in kWh = 2$\times$4 = 8kWh
Assume the cost of one unit is 6 Rs.
So cost using a 2 kW geyser for 4 hours = 6$\times$8 = 24 Rs.