. What is Refraction.Explain
We can use a modified form of Huygens' construction to understand reflection and refraction of light. figure shows an incident wavefront which makes an angle ‘i’ with the surface separating two media, for example, air and water. The phase speeds in the two media are v1 and v2. We can see that when the point A on the incident wavefront strikes the surface, the point B still has to travel a distance BC = AC sin i, and this takes a time t = BC/v1 = AC (sin i) / v1. After a time t, a secondary wavefront of radius v2t with A as centre would have travelled into medium 2. The secondary wavefront with C as centre would have just started, i.e.. would have zero radius. We also show a secondary wavelet originating from a point D in between A and C. Its radius is less than v2t. The wavefront in medium 2 is thus a line passing through C and tangent to the circle centered on A. We can see that the angle r' made by this refracted wavefront with the surface is given by AE = v2t = AC sin r'. Hence, t = AC (sin r'} / v2. Equating the two expressions for‘t’ gives us the law of refraction in the form sin i/sin r' = v1/v2.