Write commercial and SI units of energy. Calculate the cost of electric energy consumed by an electric heater rated with 50 W used for 2 hours daily in the month of April. The cost of one unit of electric energy is Rs. 5.

Explanation

Commercial unit of energy is kWh, SI unit of energy is Joule, `P=50 "Watt" rArr (50)/(1000) kW`
t=2 hrs., Number of days = 30 days
`E=Pxxtxx`number of days `" " E=(50)/(1000)xx2xx30 rArr 3 kWH ` (3 Units)
Cost of 1 unit = Rs. 5.00, `:. ` Cost of electric energy consumed `= Rs. 5xx3 = Rs. 15`