QQuestion
A ray of light enters a glass block from air and comes out from the opposite surface. If the angle of refraction at the first surface is not the same as the angle of incidence at the second surface, then:
(a) What is the product of the ratio sin i / sin r at the first surface and at the second surface?
(b) State whether the opposite surfaces are parallel or not parallel.
(c) How did you reach the conclusion in (b) above?
✓Answer
(a) At the first surface, from air to glass:
\frac{\sin \mathrm{i_1}}{\sin \mathrm{r_1}} = μ
At the second surface, from glass to air:
\frac{\sin \mathrm{i_2}}{\sin \mathrm{r_2}}=\frac{1}{\text{μ}}Therefore, the product is \mu\times\frac{1}{\text{μ}}=1.
(b) The opposite surfaces are not parallel.
(c) If the opposite surfaces were parallel, the angle of refraction at the first surface would equal the angle of incidence at the second surface. Since these angles are not equal, the surfaces cannot be parallel.
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