Electric energy units are often expressed in the form of “kilowatt-hours” (a) Sh

Question

Electric energy units are often expressed in the form of “kilowatt-hours” (a) Show that one kilowatt-hour (kWh) is equal to 3.6 x 106 J. (b) If a typical family of four uses electric energy at an average rate of 580 W, how many kWh would their electric bill show for one month, and (c) how many joules would this be? (d) At the cost of $0.12 per kWh, what would their monthly bill be in dollars? Does the monthly bill depend on the rate at which they use the electric energy?

I have parts A and B.

a = 3.6 x 10^6 kwh

B. = 1.3 x 10^9 J

This is my work for C and D i can't find out what i did wrong

C. 1.3X10^9 J/3.5x10^6J = 361 kwh

D. C=361kwh x .12 kwh = $43. No, because the rate depends on total energy not the rate at which it is being used.

Can you show all work please!!!!!

Explanation / Answer

Given,

one kilowatt-hour (kWh) is equal to 3.6 x 106 J

electric energy at an average rate of 580 W

At the cost of $0.12 per kWh

E = P(power) / t(time)

1 kw = 10^3 J/sec       

1kw-hr = 10^3 J/sec * 3600sec

= 3.6 * 10^6 J

If P = 580 J/sec then E(1 mo)

= 580 J/sec* 3600 sec/hr * 24hr/da * 30 da

= 1.50 * 10^9 J

So the energy used per month = 1.50 * 10^9 J / 3.6 * 10^6J/kw-hr

= 416.66 kw-hr

At $0.12 / kw-hr    

Cost = 416.66 kw-hr* $0.12 / kw-hr

= $49.99

No because the rate depends on total energy not the rate at which it is being used.

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