A prism of angle $75^\circ$ and refractive index $\sqrt{3}$ is coated with thin film of refractive index $1.5$ only at the back exit surface. To have total internal reflection at the back exit surface the incident angle must be . . . . . . .
$(\sin 15^\circ = 0.25$ and $\sin 25^\circ = 0.43)$
$(\sin 15^\circ = 0.25$ and $\sin 25^\circ = 0.43)$
- Abetween $15^\circ$ and $20^\circ$
- B$15^\circ$
- C$> 25^\circ$
- D$< 15^\circ$
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