Question

Electronic device batteries are typically rated by their capacity in milliamphours
(mAh), measuring the total charge that can be moved by the battery. If we
assume that a 3000 mAh battery operates at a constant 4 V. (A) What is the total
energy stored in the battery? (B) For how long can this battery operate a device that
consumes a constant 500 mW of power?

Answer 1

I've tried to answer b using a mixture of guesswork and units/dimensions. It would be handy to know if my answer is right. I'll have a look at a as well ...
http://perendis.webs.com

Answer 2

May have figured out both now. The answers I get look "reasonable" to me, but I don't have the answers so I can't say.
A common theme I've noticed in most of science/technology questions is just how fiddly the questioners can make them, especially by chucking awkward numbers and units at you. It may measure various "skills", but it surely tests patience. I also suspect that you can spend so much time "chasing down an answer" that I forget what the question was, and with it the principle I'm trying to understand.
At the moment, I'm trying to solve a problem in electrostatics, related to spherical harmonics and spherical polar coordinates. I THINK I understand it, but there's one lousy square root or surd that I can't match with. So, I spend time flinging surd fractions around. What was the problem ? Oh yes, calculate an electric field somewhere. Yawn
If I've got the enclosed right, then I can justify my moan here. If not, it's the dog house, I guess.