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Question
Consider a plane wave front incident on a thin convex lens. Draw a proper diagram to show how the incident wave front traverses through the lens and after refraction focusses on the focal point of the lens, giving the shape of the emergent wave front.
Solution
The new position of the wavefront at any instant (called secondary wave front) is the envelope of the secondary wavelets at that instant.
Incident wave front traversing through the lens and after refraction focusing on the focal point of the lens is shown in the figure below.
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