NEET 2026 Physics and Chemistry Paper

Concept:When the refracted ray inside a prism is parallel to its base, the prism is at the position of minimum deviation. For an equilateral prism, the angle of the prism ($A$) is $60^{\circ}$.Formula:At minimum deviation: Angle of incidence equals angle of emergence ($i = e$).Prism formula: $i + e = A + \delta$, where $\delta$ is the angle of deviation.So, $\delta = 2i - A$.Solution:Given: $i = 50^{\circ}$, $A = 60^{\circ}$ (equilateral prism).Since $QR \parallel BC$, the prism is at minimum deviation, thus $i = e$.Using $\delta = 2i - A$: $\delta = 2(50) - 60 = 100 - 60 = 40^{\circ}$.Therefore, the angle of deviation is $40^{\circ}$.Shortcut:For an equilateral prism at minimum deviation, $\delta = 2i - 60^{\circ}$. Directly substitute $i = 50^{\circ}$ to get $\delta = 40^{\circ}$.Answer:C. $40^{\circ}$