An ordinary candle lights for 4 hours and it costs $0,30. How much we pay for a 20watts light bulb's working for 4 hours ?
-
A 20W bulb consumes 20*4 = 80 Watt-hours of energy in 4 hours.
The unit of electricity you pay for is the kilowatt-hour (kWh) = 1000 Watt-hours.
80 Watt-hours = 0.08 kWh
Lets say your unit rate is 10 cents/kWh
So the cost is 0.08 kWh * 10 cents/kwh = 0.8 cents.
If your unit rate is 20 cents/kwh, the cost would be 1.6 cents. I can't imagine it would be more than this.
The unit of electricity you pay for is the kilowatt-hour (kWh) = 1000 Watt-hours.
80 Watt-hours = 0.08 kWh
Lets say your unit rate is 10 cents/kWh
So the cost is 0.08 kWh * 10 cents/kwh = 0.8 cents.
If your unit rate is 20 cents/kwh, the cost would be 1.6 cents. I can't imagine it would be more than this.