Given, the base of a prism is equilateral triangle of side 10 cm as shown in figure.
At minimum deviation, Angle of incident = Angle of prism
i.e. i = A = 60°
Angle of refraction,
r==60°2=30° Let µ be the refractive index.
Then, by Snell’s law of refraction,
µ====√3 Now, in ∆ABP, AP = AB cos 30°
==5√3cm =5√3×10−2m i.e. optical distance travelled by light along AP,
d=µ×AP=√3×5√3×10−2=15×10−2m Now, the time taken by light
(c=3×108m∕s) to travel from P to A,
t==s=5×10−10s Thus, correct answer is 5.