# Homework Help: Very simply find potential where its zero question

1. Aug 5, 2010

### Brown Arrow

Very simply "find potential where its zero" question

1. The problem statement, all variables and given/known data

A +3.0 nC char age is at x= 0cm and a -1 nC charge is at x= 4cm. At what point or points on the axis is the electric potential zero?

2. Relevant equations

V= $$\frac{kQ}{r}$$

3. The attempt at a solution

i have solved the question, first i tried two places, between the two charges, and after the second charge.

i solved for x= 3cm and x= 6cm.

now the problem is what is i want to check in the negative zone?

now is in
the formula v1+v2 =0

for r1, do i use r1= -p and r2 = 4-p, i am confused about doing it in the negative zone, do i just use the magnitude, if only magnitude, it would be r1=p and r2=4+p, which do i use?

2. Aug 5, 2010

### thrill3rnit3

Re: Very simply "find potential where its zero" question

Other than the underlined [ corrected ] part, both are actually the same. You just multiplied both sides by -1.

So you're fine either way.

3. Aug 5, 2010

### Brown Arrow

Re: Very simply "find potential where its zero" question

i did it, r1=p and r2= 4+p, i get p=6cm, now when i go back and plug in p=6 in the equation it does not satisfy, but =-6cm works, but the answer from solving the equation is p=6cm not p=-6cm, i am confused, help please.

0 = $$\frac{k(3nC)}{P}$$ + $$\frac{k(-1nC)}{4+P}$$

4. Aug 6, 2010

### thrill3rnit3

Re: Very simply "find potential where its zero" question

I solved for p using the above equation and got p= -6

Maybe something wrong with your algebra?

even with r1= -p and r2= -4-p, I still get p= -6