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COMEDK2020PhysicsElectrostatics

A charge of 0.8 C is divided into two charges Q₁ and Q₂ . These are kept at a separation of 30 ~cm . The force on Q₁ is maximum when

Options

  1. AQ₁=Q₂=0.4 C
  2. BQ₁ 0.8 C , Q₂ negligible
  3. CQ₁ negligible, Q₂ 0.8 C
  4. DQ₁=0.2 C , Q₂=0.6 C

Correct answer

A. Q₁=Q₂=0.4 C

Step-by-step solution

Given, Q₁+Q₂=0.8 C r 30 ~cm =0.3 ~m According to Coulomb's law aligned &F=k Q₁ Q₂ r² &F=k Q₁ (0.8-Q₁ ) r² aligned F=k Q₁ (0.8-Q₁ ) r² The force on Q₁ will be maximum if aligned d F d Q₁ &=0 d d Q k Q₁ (0.8-Q₁ ) r² &=0 0.8-2 Q₁ &=0 Q₁ &=0.4 C Q₂ &=0.8-Q₁ &=0.8-0.4=0.4 C aligned

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