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An em wave is propagating in a medium with a velocity \( \vec{v} = \vec{i} \). The instantaneous oscillating electric field of this em wave is along +y axis. Then the direction of oscillating magnetic field of the em wave will be along

1. -z direction
2. +z direction
3. -x direction
4. -y direction

Correct answer: +z direction

Solution

The direction of the magnetic field in an electromagnetic wave is determined by the right-hand rule. With the electric field along +y and the wave propagating along +x, the magnetic field must be along +z to satisfy the cross-product relation: \(\vec{E} \times \vec{B} = \vec{v}\).

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