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NEET2017PhysicsElectrostaticsActual

A certain charge Q is divided into two parts q and Q-q . How the charge Q and q must be related so that when q and (Q-q) is placed at a certain distance apart experience maximum electrostatic repulsion?

Options

  1. AQ=2 q
  2. BQ=3 q
  3. CQ=4 q
  4. DQ=4 q+c

Correct answer

A. Q=2 q

Step-by-step solution

The electrostatic force of repulsion between the charge q and (Q-q) at separation r is given by F= 1 4 ₀ q(Q-q) r^2 = 1 4 ₀ q Q-q^2 r^2 If F is maximum, then F / q=0 i.e. 1 4 ₀ (Q-2 q) r^2 =0 As 1 4 ₀ r^2 is constant, therefore Q-2 q=0 or Q=2 q

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