My professor asked the cost of running a hair dryer of 1500 W for 15.0 minutes for 5 days a week for 4 weeks. The utility company charged $0.60 per kWh.(adsbygoogle = window.adsbygoogle || []).push({});

Instinctively, i thought to combine 1500 W with the 15.0 minutes into my version of "kilowatt per hour".

[tex]1500 W * \frac{1 KW}{1000 W} = 1.50 kW[/tex]

[tex]1.50 min * \frac{1 hr}{60 minutes} = 0.25 hr[/tex]

thus:

[tex]\frac{1.50 kW}{0.25 hr} = 6 kW/hr[/tex]

The dryer was used 5 times a week for 4 weeks... so it was used 20 times in the 4 weeks.

[tex]6 kW/hr * 20 = 120 kW/hr[/tex]

At... $0.60 per kWh

[tex]120 kWh * 0.60 \frac{$}{kWh} = $72[/tex]

The answer was $4.5 not $72. Therefore, my concept of kWh is clearly wrong.

Can someone explain to me what kWh is intuitively? It clearly is not the amount of kW consumed in an hour.

Thanks in advance!

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# Kilowatt-hour versus kilowatt per hour

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