1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Very simply find potential where its zero question

  1. Aug 5, 2010 #1
    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= [tex]\frac{kQ}{r}[/tex]

    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.

    1op3c0.jpg

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

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

    2qxasmp.jpg

    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. jcsd
  3. Aug 5, 2010 #2

    thrill3rnit3

    User Avatar
    Gold Member

    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.
     
  4. Aug 5, 2010 #3
    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 = [tex]\frac{k(3nC)}{P}[/tex] + [tex]\frac{k(-1nC)}{4+P}[/tex]
     
  5. Aug 6, 2010 #4

    thrill3rnit3

    User Avatar
    Gold Member

    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
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook