Physics Alternating Current PMDC Conceptual Practice
PMDC Verified Question 64 of 127
In any propagating electromagnetic wave in free space, the oscillating electric field \(\vec{E}\) and magnetic field \(\vec{B}\) are:
A
Parallel to each other and parallel to the direction of propagation
B
Parallel to each other and perpendicular to the direction of propagation
C
Perpendicular to each other and parallel to the direction of propagation
D
Mutually perpendicular to each other and perpendicular to the direction of propagation
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: Mutually perpendicular to each other and perpendicular to the direction of propagation
Concept:

Electromagnetic waves are transverse waves characterized by orthogonal electric and magnetic field vectors perpendicular to the propagation vector \(\vec{k}\).

Formula / Reaction:

$$\vec{E} \perp \vec{B}, \quad \vec{E} \perp \vec{v}, \quad \vec{B} \perp \vec{v}$$

Solution:

  • The cross product \(\vec{S} = \frac{1}{\mu_0} (\vec{E} \times \vec{B})\) points along the direction of energy propagation.


  • Thus, \(\vec{E}\), \(\vec{B}\), and wave motion are mutually perpendicular.


Why other options are incorrect:

  • Opt_A, Opt_B, Opt_C: Contradict the fundamental orthogonal transverse geometry of electromagnetic waves.

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