# EMF homework help

1. Jan 11, 2010

A charge Q at a vertex of a square and another Q on the opposite corner of the square and other two charges q each of the other vertices. If the force eletrogmanetica on Q is null which the value of Q in terms of q? There is a q such that the resultant force on 4 charges is zero?

My attemp

F = (K.Q.Q)/r^2 + (K.Q.q)/r^2
F = 0
KQ^2 + KQq = 0
Q(KQ + kq) = 0
Q = - q

If q = 0 the resultant force is 0

I correct ?

2. Jan 11, 2010

### rl.bhat

Re: Emf

If the side of the square is r, the length of the diagonal is .......?
At Q three forces are acting. How are they related to get net zero force?

3. Jan 12, 2010

Re: Emf

This is my doubt

4. Jan 12, 2010

### rl.bhat

Re: Emf

To get net zero force on Q, Q and q must have opposite sign.
On charge Q, one repulsive force between Q and Q, and two attractive forces between Q and q are acting. What is the distance between Q and Q?
Equate the resultant force of two attractive with the repulsive force to find the relation between Q and q.

5. Jan 12, 2010