Concepts Of Physics MCQ Edition [Volume 2]PhysicsElectromagnetic Waves
Sunlight reaching the earth has an intensity of 1380 W m ⁻² . Assuming this light is a plane, monochromatic wave, determine the amplitudes of the electric and magnetic fields within this wave.
Options
- A2.04 10³ N C ⁻¹ and 6.80 10⁻⁶ T
- B1.02 10³ N C ⁻¹ and 3.40 10⁻⁵ T
- C5.10 10² N C ⁻¹ and 1.70 10⁻⁶ T
- D1.02 10³ N C ⁻¹ and 3.40 10⁻⁶ T
Correct answer
D. 1.02 10³ N C ⁻¹ and 3.40 10⁻⁶ T
Step-by-step solution
The intensity of an electromagnetic wave is given by: I = 1 2 ₀ c E₀^2 Rearranging for the amplitude of the electric field E₀ : E₀ = 2I ₀ c Substituting the given values I = 1380 W m ⁻² , ₀ = 8.85 10⁻¹² C ^2 N ⁻¹ m ⁻² , and c = 3 10^8 m s ⁻¹ : E₀ = 2 1380 8.85 10⁻¹² 3 10^8 E₀ = 2760 26.55 10⁻⁴ 1.02 10^3 N C ⁻¹ The amplitude of the magnetic field B₀ is related to E₀ by: B₀ = E₀ c B₀ = 1.02 10^3 3 10^8 = 3.40 10⁻⁶ T