EM Wave Propagation – Field orientations in homogeneous, isotropic media As an electromagnetic wave propagates through a homogeneous, isotropic, lossless medium, which statement is correct?
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ADirections of the electric and magnetic fields are orthogonal.
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BBoth the electric and magnetic fields are at right angles to the direction of propagation.
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CBoth (a) and (b)
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DNeither (a) nor (b)
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EFields are parallel to propagation direction
Answer
Correct Answer: Both (a) and (b)
Explanation
Introduction / Context:In free space or any homogeneous, isotropic, lossless medium, plane electromagnetic waves are transverse. This geometric relationship underlies polarization, antenna patterns, and radiative transfer models used in remote sensing.
Given Data / Assumptions:
- Medium: homogeneous, isotropic, and lossless.
- Plane-wave approximation.
Concept / Approach:For a plane wave, the electric field E, magnetic field H, and the direction of propagation k form a mutually orthogonal triad. Hence E ⟂ H, and both are ⟂ to k (the Poynting vector S is along k).
Step-by-Step Solution:Identify plane-wave property: transversality.E ⟂ H ⇒ option (a) true.E ⟂ k and H ⟂ k ⇒ option (b) true.Therefore combined statement (c) is correct.
Verification / Alternative check:Maxwell’s equations in homogeneous media lead to wave equations with ∇·E = 0 and ∇·H = 0 for plane waves, enforcing transversality.
Why Other Options Are Wrong:
- (d) contradicts wave transversality.
- (e) applies to longitudinal waves, not EM plane waves in such media.
Common Pitfalls:Assuming longitudinal components exist in free space; they appear only in waveguides/plasmas under special conditions.
Final Answer:Both (a) and (b)