Light travelling inside crown glass ( ) strikes a glass-water interface ( ) at

PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Wave propagation and light in media · Wave propagation and light in media

Optics and Photonics, Ch Reflection and transmission at interfaces

Problem

Light travelling inside crown glass (ni=1.50n_i = 1.50) strikes a glass-water interface (nt=1.33n_t = 1.33) at θi=30∘\theta_i = 30^\circ. Since ni>ntn_i > n_t this is an internal reflection; the critical angle here is θc=arcsin⁡(1.33/1.50)=62.5∘\theta_c = \arcsin(1.33/1.50) = 62.5^\circ and Brewster's angle is θB=arctan⁡(1.33/1.50)=41.6∘\theta_B = \arctan(1.33/1.50) = 41.6^\circ, so 30∘30^\circ is below both. A student claims: 'Every reflection is a half-wave reflection unless the light ends up in a denser medium, so here, going from glass into the (less dense) water, both s and p must flip by π\pi.' ((a)) Explain what is wrong with this reasoning. ((b)) Compute rsr_s and rpr_p at 30∘30^\circ and state the correct phase behaviour for each polarisation.

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