Homework Help: Zero potential, 3 charges

1. Apr 8, 2014

Lucky7

1. The problem statement, all variables and given/known data
Let us have a square ABCD (D is in the topleft corner) of size 1 m. Let us have 3 point charges situated in points B, C and D. The charges are following QB=2C, QC=-1C and QD=5C. The task is to find (a) the points/plane where the electric potential is zero and (b) two points where the electric intensity is zero.

2. Relevant equations
ψ = (1/(4*pi*epsilon))* (Q1/r1+Q2/r2+Q3/r3)=0

3. The attempt at a solution
According to the equation mentioned above I obtain the following equation
2/rB-1/rC+5/rD=0
But now what? Is my current procedure OK?

Last edited: Apr 8, 2014
2. Apr 8, 2014

BvU

Your procedure is OK. If (a) asks for the points in the plane where the potential is zero, you can write it out in x and y and try to solve. Expect to end up rather close to C. in 3D it becomes a deformed sphere.

3. Apr 9, 2014

Lucky7

How do I write it in x,y? And why in 3D, I should find the points in 2D not 3D.
Any hint to (b)?

4. Apr 9, 2014

Anyone?

5. Apr 9, 2014

BvU

"I should find the points in 2D not 3D" Good thing you tell us, because it's nowherer in the original posting.

If (x,y) is a point in the x,y plane, what is the expression for rB ?

Wrt (b), does the problem ask for electric intensity, or does it ask for electric field strength ? If so, do you have a relevant equation available ?