# Homework Help: Electric Potential and Electric Energy

1. May 27, 2013

### totallyclone

1. The problem statement, all variables and given/known data
Consider point a which is 65 cm noth of a -2.8μC point charge, and point b which is 80 cm west of the charge. Determine (a) Vba=Vb-Va, and (b) Eb-Ea (magnitude and direction)

2. Relevant equations
k=9x10-9
V=kQ/r
V=kQ(1/rb-1/ra)
E=kQ/r2
E=kQ(1/rb2-1/ra2)

3. The attempt at a solution
(a) Vba=Vb-Va
=kQ(1/rb-1/ra)
=(9x10-9)(-2.8x10-6)(1/0.8-1/0.65)
=7.269x10-15 V

(b) Eb-Ea
=kQ(1/rb2-1/ra2)
=(9x10-9)(-2.8x10-6)(1/0.82-1/0.652)
=2.027x10-14 N/C

I may have mistakes. I wonder if it's right. So I found the magnitude for (b) but I'm not quite sure about the direction (since it has a negative magnitude)? :shy:

Last edited: May 27, 2013
2. May 27, 2013

### Staff: Mentor

Realize that Eb and Ea are vectors. You must subtract them as vectors.

3. May 27, 2013

### totallyclone

So I have to separate them to their own X and Y components??

4. May 27, 2013

### Staff: Mentor

Sure, that's one way of doing it.