An incident ray is parallel to emergent ray in refraction as the angle of incidence is equal to the angle of emergence.Let the refractive index of the medium be = uSnell\’s law is a theory used to describe the relationship between incidence and refraction angles when referring to light or other waves crossing a boundary between two separate isotropic mediums, such as water, glass or air.According to snell\’s law -sin i/sin r = u — 1sin r/ sin e = 1/u — 2Multiplying equation 1 and 2 -= sin i/ sine = 1= sin i = sin eTherefore ∠e = ∠i and are parallel.
By using Snell theorem of refraction,n21 = sin i / sin rn21 = 1 / n12n12 = sin r / sin en21 = sin e / sin rsin i / sin r = sin e / sin rThus, sin i = sin eTherefore, Incident ray is parallel to emergent ray.