Answer: u = ε_0 E² = B²/μ_0 (each term equal at any instant).
- A u = ε_0 E² = B²/μ_0 (each term equal at any instant)
- B u = ε_0 E² mainly, ignoring the magnetic field's contribution largely
- C u = B²/μ_0 mainly, ignoring the electric field's contribution largely
- D u = E² + B², adding the fields without their respective constants
Correct answer: A. u = ε_0 E² = B²/μ_0 (each term equal at any instant)
Explanation: Total energy density u = ½ε_0 E² + ½B²/μ_0. At any instant, ½ε_0 E² = ½B²/μ_0 (equal electric and magnetic energy densities). Total u = ε_0 E² = B²/μ_0.
In an electromagnetic wave, the oscillating electric field (E) and magnetic field (B) are perpendicular to each other and to the direction the wave travels - a purely transverse wave that needs no medium, unlike sound.
Concept context
Maxwell's equations, EM spectrum, properties, and applications of each band.