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A laser beam of power 27   mW has a cross-sectional area of 10   mm 2 . The magnitude of the maximum electric field in this electromagnetic wave is given by [Take ε 0 ≈ 9 × 10 - 12   C 2   N - 1   m - 2 and c = 3 × 10 8   m   s - 1 ]

Options

  1. A1   kV / m
  2. B1 . 4 kV / m
  3. C0 . 7   kV / m
  4. D2   kV / m

Correct answer

B. 1 . 4 kV / m

Step-by-step solution

I = P A = 1 2 ε 0 E 0 2 c ∴ E 0 = 2 P ε 0 c A = 2 × 27 × 10 - 3 9 × 10 - 12 × 3 × 10 8 × 10 × 10 - 6 ⇒ E 0 = 1 . 4   kV / m

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