CBSE Class 12 · 2008 · Geometrical OpticsVery Short Answer

What is the geometrical shape of the wavefront when a plane wavefront passes through a convex lens?

Answer: A converging spherical wavefront (spherical, converging towards the focus of the lens).

Solution

A convex lens is thicker at the centre, so the central portion of the plane wavefront is retarded more than the edges. The emergent wavefront therefore curves inward and becomes a \emph{spherical wavefront converging} to the focus.

CBSE Class 12 Board · 2008 · Subjective

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