# Electromagnetic forces, finding alpha.

1. Jun 15, 2011

### sphys4

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

When a third charge is placed at the origin, it is found that the force on it is zero. Find alpha?

Two charges Q and 5Q are located as shown in the figure below.
https://chip.physics.purdue.edu/protected/GiordanoEMimg/chapter17/17prob16.jpg

If possible, please show work so i can learn how to do it. Thanks!

2. Relevant equations

3. The attempt at a solution
I know that force varies as a function of charge and inversely proportional to square of distance.
So i need to use this equation somehow:
F = k Qa Qb / d^2
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jun 15, 2011

### ideasrule

That link can only be accessed by Purdue University students. Can you attach the image instead?

3. Jun 16, 2011

### sphys4

4. Jun 16, 2011

### Staff: Mentor

So suppose that some charge, q, was placed at the origin. What would be the formula for the force on it due to the charge Q? (And for the sake of argument, suppose for now that all the charges, q, Q, and 5Q are positive).