STANDARDPhysics-Electromagnetic Waves
STANDARD Physics Energy Density MCQ Question
Type: MCQ-numerical-Medium-Class 12
A plane electromagnetic wave with electric field of amplitude 4 V m⁻¹ varies with time propagating along z-axis. The average energy density of the magnetic field (in J m⁻³) is
A
33.29 × 10⁻¹²
B
35.4 × 10⁻¹²
C
37.72 × 10⁻¹²
D
30.1 × 10⁻¹²
Correct Answer
Option B
Detailed Explanation
Amplitude of electric field and magnetic field are related by the relation E₀/B₀ = c. Average energy density of the magnetic field is uₘ = ½B₀²/μ₀ = ½(E₀/c)²/μ₀ = 35.4 × 10⁻¹² J m⁻³.
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