Why doesn't potential become negative when closer than infinity in Griffiths?

[kq6up]

I am reviewing in Griffith's E&M, and I find that potential is defined as zero at infinity (that bits fine). However, should not an object that distance from a charge be less than zero (negative) if it is closer than infinity? It seems it should as it has lost P.E. However, he doesn't seem to use this convention.

Another thought: I have just finished Mechanics in where these inverse square law problems are always attractive. I guess if my test charge was positive and the charge in question was also positive, my forces would be repulsive, and actually increasing potential as I move closer -- maybe that is why I am confused.

Thanks,
Chris

 

[Doc Al]

I guess if my test charge was positive and the charge in question was also positive, my forces would be repulsive, and actually increasing potential as I move closer -- maybe that is why I am confused.

Sounds like you figured it out for yourself! ;)

The potential about a positive charge is zero at infinity and increases as you get closer. Imagine that positive test charge being repulsed.

 

[kq6up]

Yes, as I was writing the question it dawned on me :D

Chris