Question

Are ${R_1}$ , ${R_2}$ , ${R_3}$ , ${R_4}$ and ${R_5}$ in phase.

A. Yes
B. No
C. Maintain a constant phase
D. Insufficient data to reply

Answer 1

This is the concept of Huygens’s wave theory. He proposed that in the case of reflection of light, the angle of incidence is equal to the angle of reflection of the light. Also, the angle of reflection and angle of incidence of the light lies at $90^\circ$ to the point of incidence of the light.

Complete step by step answer:
Here, let a light is incident to the denser medium as shown below

- Here, ${R_1}$ is the ray reflected from the water, ${R_2}$ is the ray reflected from guanine, ${R_3}$ is the ray reflected from the cytoplasm, ${R_4}$ is the ray reflected from an amine, and ${R_5}$ is the ray reflected from the cytoplasm having refractive index $\dfrac{4}{3}$.
- As we can say, there is a half-cycle phase shift from the water to the guanine interface. This half-cycle shift continues for all the interfaces up to the cytoplasm of refractive index $\dfrac{4}{3}$. But there is no half-cycle shift from the guanine ($n = 1.8$) interface.
- Therefore, we can say that due to reflections there is one half-cycle phase shift in the two neighboring reflected rays. Therefore, rays ${R_1}$ , ${R_2}$ , ${R_3}$ , ${R_4}$ and ${R_5}$ maintain a constant phase.

So, the correct answer is “Option C”.

Note:
Huygens principle states that when a light is incident on an arbitrary surface the wave front itself forms spherical wavelets and these wavelets are always directed in the forward direction. Therefore, every wave front acts as a source of secondary wavelets. Also, propagation of light waves is equal to the sum of wavelets formed spreading from each point of the wave front.