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JEE Main202127 Aug 2021Morning ShiftPhysicsElectrostaticsActual

A uniformly charged disc of radius R having surface charge density σ is placed in the x y plane with its center at the origin. Find the electric field intensity along the z -axis at a distance Z from origin:

Options

  1. AE = 2 ε 0 σ 1 Z 2 + R 2 1 / 2 + Z
  2. BE = σ 2 ε 0 1 + Z Z 2 + R 2 1 / 2
  3. CE = σ 2 ε 0 1 - Z Z 2 + R 2 1 / 2
  4. DE = σ 2 ε 0 1 Z 2 + R 2 + 1 Z 2

Correct answer

C. E = σ 2 ε 0 1 - Z Z 2 + R 2 1 / 2

Step-by-step solution

E = ∫ 0 R 1 4 π ε 0 × σ × 2 π x d x × x x 2 + Z 2 3 2 = σ 2 ε 0 1 - Z Z 2 + R 2 1 / 2

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