Here is a drawing: http://imgur.com/VdW1Xmv

Trying to solve this question. I understand that the charge in the center needs to be positive, and the sum of all forces should be 0.

But how do I express the magnitude of the charge in the center, how do I find it? I know vectors need to be used, but not sure between which charges, just between the electrons to the positive charge, or all the vectors between all 5 charges?

Help please, so confused.

## Best Answer

For every particle, the sum of forces from all the other particles needs to be zero. Consider one particle in the corner - write down the sum of forces from the other four paricles (corners plus center) using couloumbs law in vector form. The sum has one unknown which is the unknown charge. Solve for this.