Electric Potential & Energy: Significance & Difference

[Jalo]

Homework Statement

Can anyone tell me the significance of the sign of the electric potential between two charges?
For example, If I have two charges of different sign the electric potential between them will be negative, and it will represent the energy necessary to separate them between the initial distance, d, until d→∞.
What if both charges are positive? The electric potential will be positive. What does it represent? The energy required to move them from distance d until d→0 ? The energy that the particles would acquire as d→∞ ?

Also, what's the difference between electric potential and electric potential energy? I know that electric potential only requires a source charge, while electric potential energy describes the electric potential of a charge at some given point, but I can't quite understand the concept of both.

I'm sorry if those doubts are a little idiot, but I'm trying to learn electromagnetism on my own and the book I'm reading didn't cover those concepts very well, and I feel like I should understand all this basic stuff to be able to fully understand magnetism. Thanks for your time.

Homework Equations

The Attempt at a Solution

 

[pgardn]

Look at the units of both electric potential and electric potential energy. That might help. And then ask yourself how you would describe the difference. And then think about circuits and why we use Electric potential difference so often. Why ohms law involves electric pot. difference...
Also look at why defining an electric potential can be an arbitrary thing to make a problem easier for you.

If you look at two places in an electric field and one is labeled 0 V and one is labeled +4V. Then, You look at two places in space in a different electric field and one is labeled -2V and one is labeled +2V. But they really have the same potential difference...? And why even label one positive and negative...?

And why gravitational potential energy, when dealing with planets goes from some negative number at the surface and then approaches zero. Yet in doing conservation of energy problems on the surface of the Earth for example, an object can be given a quantity you can call mgh and yet you can make h a reference point that you decide to help you solve a problem(ie you can play with h). Once I understood the basic answers to all these, I understood the difference between electric potential, electric potential difference, electric potential energy much better.

When I learned this I found this video helpful.
http://video.google.com/videoplay?docid=-7402356853085875933

I also enjoyed the way Prof. Lewin draws his dashed chalk lines.