Question

In an electromagnetic wave, the electric field and magnetic field are:

• A. Parallel to each other
• B. Anti-parallel to each other
• C. Perpendicular to each other and to the direction of propagation
• D. Parallel to the direction of propagation

Hint:

Remember the Mutually Orthogonal Rule for EM waves: The electric field, the magnetic field, and the direction of wave travel are all at right angles ($90^\circ$) to one another.

Answer 1

The Correct Option is C

Concept: Electromagnetic waves (EM waves) are self-propagating transverse oscillations of electric and magnetic fields traveling through space. Their transverse nature is directly defined by Maxwell's equations.

Step 1: Analyze the spatial orientation of field vectors.
In an electromagnetic wave, the oscillating electric field vector ($\vec{E}$) and the magnetic field vector ($\vec{B}$) vary in phase, but they oscillate along paths that are exactly perpendicular (at $90^{\circ}$) to one another.

Step 2: Determine orientation relative to the direction of wave travel.
The direction in which the EM wave carries energy is given by the Poynting vector ($\vec{S}$), which follows the right-hand cross product rule: \[ \vec{S} = \frac{1}{\mu_0} \left( \vec{E} \times \vec{B} \right) \] Because the cross product of two vectors is always Perpendicular to both of them, the direction of wave propagation is simultaneously perpendicular to both the electric field $\vec{E}$ and the magnetic field $\vec{B}$. Thus, $\vec{E}$, $\vec{B}$, and the propagation vector $\vec{k}$ form a mutually orthogonal triad.