An electromagnetic wave is transporting energy in the negative z-direction. At a certain point and instant, the electric field is along the positive y-direction. What is the direction of the magnetic field at that point and instant?
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Question

An electromagnetic wave is transporting energy in the negative z-direction. At a certain point and instant, the electric field is along the positive y-direction. What is the direction of the magnetic field at that point and instant?

Options

G1 Physics · Accepted Answer

The direction of energy propagation is along E⃗ × B⃗. We need (+ĵ) × B⃗ = -k̂. Since ĵ × î = -k̂, the magnetic field must be along the positive x-direction.