A certain charge Q is divided into two parts q and ( Q - q ) . How should the charges Q and q be divided so…

A certain charge Q is divided into two parts q and (Q-q). How should the charges Q and q be divided so that q and (Q-q) placed at a certain distance apart experience maximum electrostatic repulsion?
  1. Q=q2
  2. Q=2q
  3. Q=4q
  4. Q=3q

Solution

Fq=kq(Q-q)L2=kL2qQ-q2
dFdq=0 when force is maximum
dFdq=kL2[Q-2q]=0
⇒Q-2q=0⇒Q=2q

Asked in: JEE Main 2021 (20 Jul Shift 1)

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