# Homework Help: 3 Charges

1. Jun 28, 2010

### Ruleski

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

A negative charge Q1 = -8 nC is fixed on the x-axis at (x = -4, y = 0). A positive charge Q2 = +8 nC is fixed on the x-axis at (x = 4, y = 0). For the sake of reference, consider point A, at (x = 0, y = 5). All locations are in meters.

What is the sign of the x-component of the electric field at A?

What is the sign of the y-component of the electric field at A?

What is the magnitude of the electric field at A?

A third charge (q = 4 nC) is brought in from very far away and put at point A. What total potential energy is stored in all three charges?

2. Relevant equations

3. The attempt at a solution

I'm reviewing for an exam and I just dont know how to answer these questions. Any explanation would be appreciated. Thank You
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jun 29, 2010

### Feldoh

Start by drawing it out on paper. Perhaps you will notice some sort of symmetry between the two charges and the point A.