Multiple Choice
Which of the following best describes a key difference between electromagnetic waves and mechanical waves?
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32. Electromagnetic Waves
Intro to Electromagnetic (EM) Waves
Multiple Choice
Which of the following statements is true about electromagnetic waves propagating in air?
A
The electric and magnetic fields are perpendicular to each other and to the direction of propagation.
B
Only the electric field oscillates; the magnetic field remains constant.
C
Electromagnetic waves in air require a medium with free charges to propagate.
D
The electric and magnetic fields are parallel to the direction of propagation.
Verified step by step guidance1
Recall the fundamental nature of electromagnetic (EM) waves: they consist of oscillating electric and magnetic fields that propagate through space.
Understand that in an EM wave, the electric field \( \mathbf{E} \) and magnetic field \( \mathbf{B} \) are always perpendicular to each other.
Recognize that both \( \mathbf{E} \) and \( \mathbf{B} \) fields are also perpendicular to the direction of wave propagation, forming a mutually orthogonal set of vectors.
Note that electromagnetic waves do not require a medium with free charges to propagate; they can travel through a vacuum (or air) because they are self-sustaining oscillations of electric and magnetic fields.
Conclude that the correct statement is: 'The electric \( \mathbf{E} \) and magnetic \( \mathbf{B} \) fields are perpendicular to each other and to the direction of propagation.'
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