An electromagnetic wave travels in free space along the x-direction. At a particular point in space and time, B = 2× 10⁻⁷j T is associated with this wave. The value of corresponding electric field E at this point is _______ V/m. (a) 60 k (b) -60 k (c) 30 k (d) -600 k

Answer: (b). Magnitude: E = cB = 3× 10⁸× 2× 10⁻⁷ = 60 V/m. Direction: E must be +i with B along j. (-k) = -(k) = i, so E is along -k. So the answer is (b) -60 k V/m.

An electromagnetic wave travels in free space along the x-direction… | JEE Main 2026 (2 Apr, Shift 2)

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Nature of EM Waves & Wave Equation

An electromagnetic wave travels in free space along the x-direction. At a particular point in space and time, $\vec{B} = 2\times 10^{-7}\hat{j}$ T is associated with this wave. The value of corresponding electric field $\vec{E}$ at this point is _______ V/m.

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Answer: (b)

Magnitude: $E = cB = 3\times 10^{8}\times 2\times 10^{-7} = 60\ \text{V/m}$ .
Direction: $\vec{E}\times\vec{B}$ must be $+\hat{i}$ with $\vec{B}$ along $\hat{j}$ .
$(-\hat{k})\times\hat{j} = -(\hat{k}\times\hat{j}) = \hat{i}$ , so $\vec{E}$ is along $-\hat{k}$ .
So the answer is (b) $-60\,\hat{k}$ V/m.

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