# Average Energy Use

1. Apr 18, 2005

### NickCherryJiggz

I'm helping a friend with this question and wanted to make sure I was doing it correctly...

Suppose your local power company charges 6.3 cents per kilowatt hour and your most recent bill came to $27.00. How much energy, on average, did you use (in Joules) per second last month? Assume that the billing period covered 30 days.$27.00/(\$0.063/kilowatt hour) = 428.571428... kilowatt hours

428.57... * (3.6 x 10^6) = (1.5428571428571 * 10^9 Joules)/month = M

M / (30 * 24 * 60 * 60) = 595.23809523808 Joules/second

Thanks for the help!

2. Apr 18, 2005

### dextercioby

It's okay.U may wanna learn the concept of significant figures,though...

Daniel.

3. Apr 18, 2005

### NickCherryJiggz

Thank you, Daniel...Sorry about the sigdigs.
I know these are just silly conversions for the most part, but could someone please verify the second half of the question as well?

Now pretend that roughly 2/3 of the energy usage last month was a result of a 120 V air-conditioner, how many Coulombs of charge per second did that air-conditioner draw?

595.24... * 2/3 = 396.83...J/s
V = J/C
120 Volts = (396.83... J/s) / (Coulombs/s)
3.21 Coulombs/second

4. Apr 18, 2005

### dextercioby

It looks okay to me.

Daniel.