In the dispersion of white light by a common glass prism, which one among the following is correct ?
Red light deviates the most because red light has highest speed in prism
Blue light deviates the most because blue light has highest speed in prism
Red light deviates the most because red light has lowest speed in prism
Blue light deviates the most because blue light has lowest speed in prism
Answer is Wrong!
Answer is Right!
This question was previously asked in
UPSC NDA-1 – 2023
– In most transparent materials (normal dispersion), refractive index decreases as wavelength increases (n_violet > n_blue > … > n_red).
– Deviation (δ) in a prism depends on the refractive index (for a small angle prism, δ ≈ (n-1)A). Higher n means greater deviation.
– Speed of light in the medium (v) is inversely proportional to the refractive index (v = c/n). Higher n means lower speed.
– Thus, blue light has a higher refractive index, deviates the most, and has the lowest speed in the prism.