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A diverging beam of light from apoint source S having divergence angle alpha, falls symmetrically on a glass slab as shown. The angles of incidence of the two extrem rays are equal. If the thickness of the glass slab is t and the refractive index n, then the divergence angle of the emergent beam is |
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Answer» <P>zero Applying Snell's law at P,`(1)/(2)n=(sinalpha//2)/(sinr)` (i) Applying Snell's law at Q, `(1)/(2)n=(sinbeta//2)/(sinr)` (ii) From Eqs. (i) and (ii), `alpha=beta` Therefore, (b) is the correct answer. ltbgt 
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