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A charged dust particle of radius 5 × 10 - 7 m is located in a horizontal electric field having an intensity of 6.28 × 10 5 V m - 1 . The surrounding medium in air with coefficient of viscosity η = 1.6 × 10 - 15 N s m - 2 . If this particle moves with a uniform horizontal speed of 0 . 01 m s - 1 , the number of electrons on it will be

Options

  1. A20
  2. B15
  3. C25
  4. D30

Correct answer

B. 15

Step-by-step solution

n e E = 6 π η r v or n = 6 π η r v e E = 6 × 3.14 × 1.6 × 10 - 5 × 5 × 10 - 7 × 0.01 1.6 × 10 - 19 × 6.28 × 10 5 = 15

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