Question

An electric iron is rated at 3kw. Electrical energy costs Rs. 4 per kwh. What is the cost of using the iron for 5 hours?

• A. Rs.12
• B. Rs. 20
• C. Rs.150
• D. Rs. 60

Answer 1

The correct option is D Rs. 60

Answer is D.
Energy ($power\times time$) is measured in Joules and by including time (t) in the power formulae, the energy dissipated by a component or circuit can be calculated.
Energy dissipated = Pt.
In this case, the power of the electric iron is rated as 3 kW and it runs for 5 hours.
Total power dissipated = 3 kW * 5 hrs = 15 kWh.
It is given that the cost of 1 kWh is Rs. 4.
Therefore, total cost = 15 kWh * 4 = Rs. 60.
Hence, the cost of using the iron for 5 hours is Rs. 60.