Q.Select the WRONG statement. (A) Smaller angle of prism is recommended for greater angular dispersion. (B) Right angled isosceles glass prism is commonly used for total internal reflection. (C) Angle of deviation is practically constant for thin prisms. (D) For emergent ray to be possible from the second refracting surface, certain minimum angle of incidence is necessary from the first surface.

[!TLDR] Dispersion delta_VR = A(n_V - n_R) grows with A, so a LARGER prism angle -- not a smaller one -- gives greater angular dispersion, making statement (A) the wrong one. [!ANS …

From the thin-prism dispersion relation delta_VR = A(n_V - n_R), angular dispersion is directly PROPORTIONAL to the prism angle A -- so a LARGER angle of prism gives MORE dispersion, not less, making statement (A) false as printed. The other three statements are each correct: (B) a right-angled isosceles glass prism is indeed the standard choice for TIR-based devices (its internal 45-degree incidence comfortably exceeds glass's roughly 42-degree critical angle); (C) the deviation of a thin prism, delta = A(n-1), is genuinely independent of the angle of incidence for small angles, i.e. practically constant; (D) an emergent ray f …

Check each statement against the derived formulas: dispersion delta_VR=A(n_V-n_R) increases with A (so smaller-angle-for-more-dispersion is false); the other three statements match the TIR- …

Assuming any prism-related quantity is minimized by a smaller angle by default, without checking the actual direct propor …