Question
Wed June 22, 2011 By: Monami Chatterjee
 

4 charges Q,q,Q&q are kept at the 4 corners of a square . what is the relation between Q and q so that the net force on a charge q is 0?

Expert Reply
Thu June 23, 2011
Let the charges are arranged on the corners of a square of side r.
 
A (Q)            B(q)
......................
.                    .
.                    .
.                    .
.                    .
......................
D(q)               C(Q)
 
The net force on the charge q placed on corner D = (1/4??0r2)[q/ 2  - sqrt{(Qq)2 + (Qq)2}]
 
For this net force to be zero, 
[q2/2  - sqrt{(Qq)2 + (Qq)2}] = 0
 
q2/2 = sqrt{(Qq)2 + (Qq)2} = Qq sqrt (2)
 
q = 2 sqrt (2) Q
 
 
 
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