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A charge Q is divided into q & (Q-q).For maximum force between them,the ratio Q/q must be____________
If the distance between the two charges is r, then the magnitude of the force between them is F= kq(Q-q)/r^2
= k(qQ-q^2)/r^2
To ?nd the value of q which give maximum F, take the derivative of F with respect to q and ?nd where it is zero.
dF/dq = k(Q-2q)/r^2
= 0
ie, Q-2q=0 which gives Q=2q , Q/q=2.


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