Question 307: Wave Optics

Question

When wavefronts pass from denser medium to rarer medium, the width of the wavefront

Accepted Answer

When wavefronts pass from a denser medium to a rarer medium, their behavior can be analyzed using the principles of wave optics, particularly refraction and Huygens' principle.
Understanding Refraction and Wavefront Behavior:
Speed and Wavelength Increase:
In a rarer medium, the speed of the wave increases because the optical density is lower.
Since the frequency of the wave remains constant (as it is determined by the source), an increase in speed results in an increase in wavelength ($ v = f \lambda $).
Wavefront Bending:
According to Snell's Law, when a wave passes from a denser to a rarer medium at an angle, it bends
away from the normal
.
This bending causes the wavefront to spread out more in the lateral direction.
Width of the Wavefront:
The "width of the wavefront" refers to the lateral extent of the wavefront perpendicular to the direction of propagation.
As the wavefront bends away from the normal, the lateral spread increases, effectively
increasing the width of the wavefront
.
Visual Explanation:
Imagine a beam of light (or any wave) passing obliquely from water (denser medium) into air (rarer medium). Upon entering the air:
The wavefronts move faster.
The beam spreads out because each point on the wavefront moves away from the normal at a greater angle.
The overall width of the beam (wavefront) increases due to this spreading.
Conclusion:
Given the above analysis, when wavefronts transition from a denser to a rarer medium, the width of the wavefront
increases
.
Answer:
Option A:
increases.

Answer

increases.

Answer

may increase or decrease.

Answer

decreases.

Answer

remains unchanged.

Wave Optics

When wavefronts pass from denser medium to rarer medium, the width of the wavefront

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