Question

The phase difference between electric wave and magnetic wave in the electromagnetic wave is

• A. \(\pi\)
• B. \(\frac{\pi}{2}\)
• C. \(\frac{\pi}{3}\)
• D. Zero

Hint:

Remember the key properties of EM waves: 1. \(\vec{E}\) and \(\vec{B}\) are mutually perpendicular. 2. The direction of propagation is given by \(\vec{E} \times \vec{B}\). 3. \(\vec{E}\) and \(\vec{B}\) are always in phase (phase difference is zero). 4. The ratio of their magnitudes is constant: \(E/B = c\) (speed of light).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
An electromagnetic (EM) wave consists of oscillating electric field (\(\vec{E}\)) and magnetic field (\(\vec{B}\)) vectors. These fields are perpendicular to each other and also perpendicular to the direction of wave propagation. A key characteristic of EM waves is the relationship between the phases of these two fields.
Step 2: Detailed Explanation:
According to Maxwell's equations for EM waves in a vacuum or free space, the electric and magnetic fields are always in phase. This means that they reach their maximum values at the same time and at the same point in space. Similarly, they both pass through zero and reach their minimum values simultaneously.
If the electric field is described by \(E = E_0 \sin(kx - \omega t)\), the magnetic field will be described by \(B = B_0 \sin(kx - \omega t)\).
The phase for both waves is the term \((kx - \omega t)\). Since the phase term is identical for both, the phase difference between them is zero.
Step 3: Final Answer:
The electric and magnetic fields in an electromagnetic wave oscillate in phase with each other. Therefore, the phase difference between them is zero. Option (D) is correct.