Electricity AS level.

I have some questions on Voltage, Current, Charge, Power all of that. Has anybody got a good analogy or way to explain it to me, so that I know exactly what they are.
Secondly, a voltmeter needs to have an infinitely high resistance. Could anybody explain to me why? As surely this would eat up the charge?

Reply 1

AlexJK

I read that the resistance of a voltmeter must be infinitely high, so that it doesn't draw any current. So I did:
V = IR,
3 = I*9.99x10^99
I = 3/9.99x10^99 on the calculator and got 0.
So this makes sense, all current still goes to the other external resistance.
Still need an analogy though!

Reply 2

dkdeath

Potential difference
Think of two water tanks connected with a tube, one being full the other one empty. If they are at the same level no water flows from tank a to b. If you start increasing the height of the full tank (give it more gravitional potential energy ) water will flow into second tank. The greater difference in gpe the more water will want to flow. Now think of each water molecule , and you define a point A on the pipe. Current is the number of water molecules flowing at that point per second. To sum it up If you increase the potential difference the water will want to flow more into the second tank, so you get more molecules flowing per second , but if this water flowing encounters resistance flow is slowed down.