Critical angle is the angle of incidence in the denser medium when the angle of refraction in the less dense medium is 90^\circ. (b) Deviation of a ray in a triangular prism is determined by the factors: - Angle of incidence - Refracting angle of the prism, and - Refractive index of the prism material. (c) A = 2r = 2 x 29 = 58\(^o\) But n = \(\frac{sin \frac{1}{2} (A + Dm)}{sin \frac{1}{2}A} \) sin \(\frac{1}{2}\)(A + Dm) = n sin A \(\frac{1}{2}\)A 58 + Dm = 93.32 - 58 = 35.32\(^o\) (d) Angle P = 45^\circ - 20^\circ = 25^\circ But Angle Q = 180^\circ- 60^\circ = 120^\circ P +Q + R = 180^\circ Hence R = 180 - (P + Q) =180 - (25 + 120) = 35^\circ (ii) n = \(\frac{Sini}{sinP} = \frac{sin45^o}{sin45^o} = 1.673\) (iii) n = \(\frac{sini}{sine} = \frac{sine}{sinR} = \frac{sinee^o}{sin35^o}\) = 1.673 = \(\frac{sine}{sin35^o}\) e = sin\(^{-1}\) (1.673 x sin 35\(^o\)) = 73.7\(^o\) (iv) D = (i + e) - A = (45 + 73.3) - 60\(^o\) = 58.3\(^o\)