Referring to Figure 9.64, why doesn’t the ray inside each of the two prisms get refracted out of the prisms at the second interface instead of turned back into the glass? Similarly, referring to Figure 9.17, why don’t the rays that undergo two reflections inside the pentaprism get refracted out of the prism at one or both of these boundaries instead of being turned back into the glass? Explain what must be happening at the glass–air interfaces in these prisms to produce the ray paths shown.

Figure 9.64

Figure 9.17

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90 75 135 60% P (a) 90 60 90 P (b) 30 60