NEET Refraction by Prism MCQs & PYQs

Using the prism formula: \(mu = \frac{sin((A+\delta_m)/2)}{sin(A/2)}\). Substituting \(mu = cosec(A/2) =\frac{1}{sin(A/2)}\), we get \(sin((A+\delta_m)/2) = 1 ⇒ (A+\delta_m)/2 = 90^0 ⇒ \delta_m = 180^0 - A\).

Dispersive power (\(\omega\)) of a prism depends only on the nature of the material of the prism, and is independent of the refracting angle and size of the prism.

For normal incidence on the first face, the angle of refraction \(r_1 = 0\), which implies \(r_2 = A\). Applying Snell's law at the second face for small angles, \(e \approx \mu r_2 = \mu A\), giving \(A \approx \frac{e}{\mu}\).

Atmospheric refraction causes sunlight to bend as it passes through Earth's atmosphere. This phenomenon makes the sun appear to rise earlier and distorts its shape into an oval or flattened form at the horizon due to differential refraction. Both Assertion (A) and Reason (R) are true, and (R) provides a correct explanation for (A).

Dispersion, the splitting of light into its constituent colors, occurs during refraction because the refractive index of a medium depends on the wavelength of light. This effect is present at any plane refractive surface. In a prism, the refractions at both surfaces cause deviations for different colors that add up in the same direction, making the overall dispersion more noticeable. Both A and R are true, and R explains A.

A prism disperses light because its non-parallel surfaces separate colors due to varying refractive indices. A rectangular slab also disperses light internally, but the emergent rays are parallel, resulting in no net angular dispersion. Dispersive power is a material property and is non-zero for any dispersive medium, including glass slabs.