COMEDK2022PhysicsElectromagnetic Waves
A 30 ~mW laser beam has a cross-sectional area of 15 ~mm ^2 . The magnitude of the maximum electric field in this electromagnetic wave is given by [ array l Permittivity of space, ₀=9 10⁻¹² Speed of light, c=3 10^8 ~m / s array ]
Options
- A1.22 kV / m
- B12 kV / m
- C10 kV / m
- D201 kV / m
Correct answer
A. 1.22 kV / m
Step-by-step solution
I = P A = 30 10⁻³ 15 10⁻⁶ = 2 10^3 , W/m ^2 I = 1 2 c ₀ E₀^2 E₀^2 = 2I c ₀ E₀^2 = 2 2 10^3 3 10^8 9 10⁻¹² = 4 10^3 27 10⁻⁴ = 40 27 10^6 E₀ = 40 27 10^3 1.22 10^3 , V/m = 1.22 , kV/m Correct option: (1)