# Electrical Energy and Power

## Answers and Replies

14 days times 40 w; thats 24*14 *.04=13.4 KW-hrs times 12 cents=what you say. Post the rest of the results,I'd be curious.

I'm not a maths expert, but you're logic seems to make sense, even though the answer is quite small. I worked it out in a similar way to you:

energy transfered or total units (Kw/h) = power (kw) x time (h).

Then

total cost = number of units x cost per unit.

Perhaps, 40W is not a lot of power? The average hairdryer is 1.5kw

chroot
Staff Emeritus
Science Advisor
Gold Member
Your answer is correct to part a.

Part of the reason we consume such an enormous amount of resources in the US is precisely because the price of those resources is so low compared to other places in the world. 40W is currently an almost insignificant amount of power in terms of its cost, but this might not always be so.

- Warren

Thanks for all the replies. =]
As to denverdoc, here's what I got for part b) and c):

$$b) \frac{0.120}{kWh}*0.970kW*0.05h= 0.00582$$
b) $0.00582 o_0 is this correct?? $$c) \frac{0.120}{kWh}*5.2kW*0.667h= 0.416208$$ b)$ 0.416208

Thanks. Theres something to be said for air drying ones clothes the old fashioned way.

My only issue I see with the answers are the number of significant figures; rremember that the answer should have no more sig figs than the number with the least:

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch1/sigfigs.html

So answer b should be .01, etc

Last edited:
Thanks. Theres something to be said for air drying ones clothes the old fashioned way.

My only issue I see with the answers are the number of significant figures; rremember that the answer should have no more sig figs than the number with the least:

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch1/sigfigs.html

So answer b should be .01, etc

No problem. =] Thanks for reminding me of the sig figs