A glass prism surface is replaced from air contact to water contact. For the same internal incidence angle, TIR becomes:
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Question

A glass prism surface is replaced from air contact to water contact. For the same internal incidence angle, TIR becomes:

G1 Physics · Accepted Answer

The rarer-side refractive index increases, so sinC=μrarer/μdenser increases and C increases. Hence a larger incidence is required for TIR.