Question

Monochromatic ray of light incident on a glass prism does not produce the phenomenon of

• A. dispersion
• B. refraction
• C. deviation
• D. reflection
• E. total internal reflection

Hint:

White light is polychromatic. A prism disperses white light because different colors have different speeds in glass.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The question asks which phenomenon does NOT occur when a monochromatic light ray passes through a prism. Monochromatic light is light of a single wavelength (and thus a single color).
Step 2: Detailed Explanation:
Let's analyze each phenomenon in the context of light passing through a prism:
(A) Dispersion: Dispersion is the splitting of white light into its constituent colors (like a rainbow). This happens because the refractive index (\(n\)) of the prism material depends on the wavelength (\(\lambda\)) of light (\(n = n(\lambda)\)). Since different colors have different wavelengths, they bend by slightly different amounts, causing them to separate. However, monochromatic light consists of only one wavelength. With nothing to split into, the phenomenon of dispersion cannot occur.
(B) Refraction: Refraction is the bending of light as it passes from one medium to another (e.g., from air into glass, and from glass back into air). This will happen at both surfaces of the prism as long as the light ray is not incident perpendicular to the surface. A monochromatic ray will still bend.
(C) Deviation: Deviation is the overall change in the direction of the light ray after it has passed through the prism. This is a direct consequence of the two refractions at the prism surfaces. A monochromatic ray will be deviated from its original path.
(D) Reflection: Whenever light hits a boundary between two different media, some of it is reflected. This is known as partial reflection. So, some of the monochromatic light will reflect off both the first and second surfaces of the prism.
(E) Total Internal Reflection (TIR): If the angle of incidence of the light ray on the second surface (from inside the prism) is greater than the critical angle for the glass-air interface, the ray will be totally internally reflected instead of refracting out. This phenomenon is possible for a monochromatic ray under the right conditions of incidence angle and prism angle.
Step 3: Final Answer:
The only phenomenon listed that requires light of multiple wavelengths is dispersion. Therefore, a monochromatic ray will not produce dispersion. This corresponds to option (A).