How to count capacity of electrical service panel?

The electrical service panel in my house is physically full, but I'd like to know if additional amperage can be added. How do I count? Just add up the 120V amperages printed on the breaker switches? Do I count the bracketed-together 240V switches the same? Any tips? Then how do I know what the whole panel is rated, and what service is supplied to my house?

What is the difference between electrical impedence and resistance?

I'm doing psychophysiology and they're teaching us basic (very basic) electrical stuff so we don't fry anyone. I haven't quite got the gist of this though. Can you help? Please keep it simple! Thanks... :-)

What is the difference between electrical potential and electricity?

I was talking to my friend about neurons in the brain and the topic of electricity came up. Apparently brains do not use electricity but electrical potential (with the possible exeptions of frogs) but I cannot find infomation on this in my textbooks, perhaps they are simplified? could someone please explain this concept. Sorry for my poor english.

How much harder is engineering math compared to electrician?

I like math and it's a strong point for me with becoming an electrician. I took the tech courses to and understand trigonometry and precalculus. Do you think it would be possible for me to do engineering math to get a degree. I'm not a kid, and I have young children.

What kind of Electrical Outlet Adapter will I need to go to China?

I am planning to go on a trip to China and I know that China uses a different type of electrical outlet, What kind of converter or adapter will I need to make my US electronics work with it? I will most likely be spending my time at a relatives house, so I wont be able to receive stuff from hotels or anything.