Question

Suppose the electric company charges 10 cents per kwh. how much does it cost to use a 125 watt lamp 4 hours a day for 30 days

Answer 1

The total time the lamp was on is

`t=4 h \cdot 30 d=120 h`
Since the power is P=125 W, the total energy consumed by the lamp is

`E=Pt=(125 W)(120 h)=15000 Wh=15 kWh`
Each 1 kWh costs 10 cents, so the total cost will be

`15 kWh \cdot 10 (cent)/(kWh)=150 cents=1.50` dollars.