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EXTENSION, 1 Define (i) refraction (ii) Snell’s Law., 2. What is the cause of refraction.», 3. What are the laws of refraction., 4 Define the principle of reversibility of path of, light., , What do you mean by refractive index of a, medium ? what is its unit ?, , Name two factors on which the refractive index, , of a medium depends.