Question

At what value of the angle of incident θ₁ is a shaft of light reflected from the surface of water perpendicular to the refracted shaft?

Answer 1

Let PQ be the surface of water and n be the R.I. of water. Let AO is the shaft of light with incident angle θ₁ and OB and OC are the reflected and refracted light rays at angles θ₁ and θ₂ respectively (Fig.). From the figure 

From the law of refraction at the interface PQ