# Electric Potential Difference Problem

## Homework Statement

Two charges, A (-3 C) and B (+4 C), are placed 2.40 m apart. Point X is 30 cm from A, and Point Y is 30 cm from B. What is the electrical potential difference going from X to Y?

W = △Vq

## The Attempt at a Solution

Teacher gave answer as 6.9 x 10^4 V

I am not sure whether or not to use electric force or electric potential energy in this problem. I've tried both but obviously I cannot apply it appropriately to get the answer above.

haruspex
Homework Helper
Gold Member
Two charges, A (-3 C) and B (+4 C), are placed 2.40 m apart. Point X is 30 cm from A, and Point Y is 30 cm from B. What is the electrical potential difference going from X to Y?
That's not enough information. You need to be able to work out how far X is from B and how far Y is from A as well. Have you stated the whole question exactly as given to you?

You do not need to consider forces or energy. It is entirely to do with electric potential (which is not the same as electrical potential energy).
Once you have all the distance information, there are just two other things you need to know:
- the formula for the potential caused by a point charge q at distance r from it
- that potentials add, i.e. the net potential at a point in space is the sum of the potentials there caused by all the charges in the system

• Noah2305
Is this a 1D problem or a 2D problem? You need to draw a sketch of the locations under consideration.

If charges A and B are 2.40 m away from each other then point X is 1.8 m away from B and point Y is 1.8 m away from A.

Here's a diagram if this helps:
2.40 m
|---------------------------------|
A_____x________________y_____B
30 cm30 cm

Ignore the  it is just used for spacing. Hopefully this helps.

Also:

V = kQ / d

So it seems like it is a one dimensional problem. Have you been introduced how to calculate electrical fields yet ?

haruspex
Homework Helper
Gold Member
then point X is 1.8 m away from B and point Y is 1.8 m away from A.
Not according to the diagram. Try calculating those again.
Once you have distances right, use the formula you quote to find the potential that charge A creates at X and the potential that charge B creates at X.

haruspex