Given below are two statements :
Statement I : When the white light passed through a prism, the red light bends lesser than yellow and violet.
Statement II : The refractive indices are different for different wavelengths in dispersive medium. In the light of the above statements, chose the correct answer from the options given below :

Solution

Physics sir · 3 steps

Deviation in a thin prism goes as μ - 1, and μ is smallest for red, so red bends the least.

1. Check Statement II. In a dispersive medium like glass, the refractive index depends on wavelength. By Cauchy's relation μ = A + B/λ², a longer wavelength gives a smaller μ. So Statement II is true.

   δ = (μ - 1)A

2. Check Statement I. For a thin prism of angle A, the deviation grows with μ. Red has the longest wavelength, so μ_(red) < μ_(yellow) < μᵥᵢₒₗₑₜ, which gives δ_(red) < δ_(yellow) < δᵥᵢₒₗₑₜ. Red bends less than yellow and violet, so Statement I is true.
3. So. Both statements are true, and Statement II is the reason behind Statement I. The answer is (a).

The idea to keep. Longer wavelength means smaller refractive index, and that means less bending. In VIBGYOR, red deviates least and violet deviates most.

Answer from the NTA final answer key. Solution by PrepWiser.