In an electromagnetic wave, if \( \vec{B} \) and \( \vec{E} \) represent the magnetic field and electric field respectively, then the direction of propagation of electromagnetic wave is along the direction of
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \( \vec{E}\times\vec{B} \)
An electromagnetic wave is transverse: the electric and magnetic fields are perpendicular to each other and to the direction in which the wave travels. So the direction of propagation cannot be along \( \vec{E} \) or along \( \vec{B} \).
The sense of travel is fixed by the order of the fields: the wave moves along \( \vec{E}\times\vec{B} \). For example, with \( \vec{E} \) along x and \( \vec{B} \) along y, the wave travels along \( \hat{\imath}\times\hat{\jmath} = \hat{k} \), the z-direction. Reversing the order, \( \vec{B}\times\vec{E} \), gives the opposite direction, which is why the order of the cross product matters here.
Note: The same question was also asked in CUET (UG) 2026 on 30-05-2026 (Slot 1).
NCERT Exemplar:
Electromagnetic Waves – …
