The electric and magnetic field of an electromagnetic wave are
A
in opposite phase and perpendicular to each other
B
in opposite phase and parallel to each other
C
in phase and perpendicular to each other
D
in phase and parallel to each other
The answer is C.
Solution
A time-varying magnetic field produces an electric field and a time-varying electric field produces a magnetic field; this mutual generation sustains the wave. In an electromagnetic wave, $\vec{E} \perp \vec{B}$, and both are perpendicular to the direction of propagation. Both $\vec{E}$ and $\vec{B}$ are in the same phase: they reach their maximum and zero values at the same time and place. $E = E_0\sin(\omega t - kx)$ $B = B_0\sin(\omega t - kx)$ The electromagnetic wave travels in the direction of $\vec{E} \times \vec{B}$. So the electric and magnetic fields are in phase and perpendicular to each other.
ConceptPhase and direction of E and B
Nature of electromagnetic waves in past papers
3 questions from this chapter have appeared across 3 exam years.
