Problem 2. How is a wavefront diffe...
Question

# Problem 2. How is a wavefront different from a ray ? Draw the geometrical shape of the wavefronts when (i) light diverges from a point source, and (ii) light emerges out of convex lens when a point source is placed at its focus. [CBSE D 05]

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Solution. A wavefront is a surface obtained by joining all points vibrating in the same phase. A ray is line drawn perpendicular to the wavefront in the direction of propagation of light wave. The wavefronts of light emerging from a point source are spherical as shown in Fig. ( 10.53(a) . ) When a point source is placed at the focus of a convex lens, the emer- ging light has plane wavefronts, as shown in Fig. ( 10.53(b) ). Fig. 10.53 ( (a) ) Problem 3. If ( varepsilon_{0} ) and ( mu_{0} ) are the permittivity and permeability of free space and ( varepsilon ) and ( mu ) are corresponding quantities for a medium, then show that the refractive ndex of the medium is ( sqrt{frac{mu varepsilon}{mu varepsilon_{0}}} )