Question

Which colour has minimum angle of deviation ?

• A. green
• B. yellow
• C. red
• D. orange

Hint:

When white light passes through a prism, it splits into VIBGYOR:
{V}iolet: Bends the {M}ost (Maximum deviation) - Shortest wavelength.
{I}ndigo
{B}lue
{G}reen
{Y}ellow
{O}range
{R}ed: Bends the {L}east (Minimum deviation) - Longest wavelength. So, red light has the minimum angle of deviation.

Answer 1

The Correct Option is C

Concept: When white light passes through a prism, it undergoes dispersion, splitting into its constituent colors (the spectrum: Violet, Indigo, Blue, Green, Yellow, Orange, Red - VIBGYOR). Each color is deviated (bent) by a different amount. The angle of deviation depends on the refractive index of the prism material for that particular color (wavelength) of light. Step 1: Relationship between Refractive Index, Wavelength, and Deviation
The refractive index (\(n\)) of a material generally decreases as the wavelength (\(\lambda\)) of light increases. \[ \text{Shorter wavelength (e.g., Violet, Blue)} \rightarrow \text{Higher refractive index} \] \[ \text{Longer wavelength (e.g., Red, Orange)} \rightarrow \text{Lower refractive index} \]
The angle of deviation (\(\delta\)) produced by a prism increases with an increase in the refractive index of its material (for a given prism angle and angle of incidence). \[ \text{Higher refractive index} \rightarrow \text{Greater deviation} \] \[ \text{Lower refractive index} \rightarrow \text{Lesser deviation} \] Step 2: Order of Wavelengths for Visible Light The colors of the visible spectrum, in order of increasing wavelength (and thus decreasing refractive index and decreasing deviation), are approximately: Violet (shortest \(\lambda\)) \(\rightarrow\) Indigo \(\rightarrow\) Blue \(\rightarrow\) Green \(\rightarrow\) Yellow \(\rightarrow\) Orange \(\rightarrow\) Red (longest \(\lambda\)) Step 3: Determining Minimum Angle of Deviation Since deviation is least for the color with the lowest refractive index, and the lowest refractive index corresponds to the longest wavelength:
Violet light (shortest wavelength) has the highest refractive index for the prism material and thus undergoes the {maximum} deviation.
Red light (longest wavelength) has the lowest refractive index for the prism material and thus undergoes the {minimum} deviation. Step 4: Analyzing the options Comparing the given colors based on their position in the spectrum (VIBGYOR, from max deviation to min deviation):
Green
Yellow (deviates less than green)
Red (deviates least among all visible colors)
Orange (deviates less than yellow, but more than red) The color with the minimum angle of deviation will be the one with the longest wavelength among the options, which is Red. Therefore, red colour has the minimum angle of deviation when white light passes through a prism.