An electromagnetic wave in vacuum has magnetic-field x-component Bₓ = B₀ cos(ky + ωt). The corresponding electric field is:
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Question

An electromagnetic wave in vacuum has magnetic-field x-component Bₓ = B₀ cos(ky + ωt). The corresponding electric field is:

G1 Physics · Accepted Answer

The phase ky + ωt represents propagation along −y. For an electromagnetic wave, E × B = direction of propagation. Here B is along +x. To make E × B point along −y, E must be along −z because (−z) × (+x) = −y. Also, E₀ = cB₀. Hence the electric field is along −z with magnitude cB₀ cos(ky + ωt). Correct option: B.