A plane EM wave propagates along the positive x-axis. Which given pair of electric-field and magnetic-field directions is consistent with Maxwell's transverse-wave condition and E⃗ × B⃗ along +x? [Image]
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Question

A plane EM wave propagates along the positive x-axis. Which given pair of electric-field and magnetic-field directions is consistent with Maxwell's transverse-wave condition and E⃗ × B⃗ along +x? [Image]

Options

G1 Physics · Accepted Answer

Step 1: E⃗, B⃗ and the propagation direction of a plane electromagnetic wave must be mutually perpendicular. Step 2: The direction of propagation is parallel to the Poynting vector, i.e. E⃗×B⃗. For propagation along +x, this cross product must point along +î. Step 3: Option B has E⃗ = −ĵ + k̂ and B⃗ = −ĵ − k̂. Step 4: E⃗·B⃗= (+1)−1=0 and E⃗×B⃗ = 2î, so option B satisfies both requirements. Final answer: (B) −ĵ + k̂ ; −ĵ − k̂.