The critical angle for a medium of refractive index 1.5 is closest to

Explanation

The sine of the critical angle equals one over the refractive index, so sin C is 0.667 and C is about 42 degrees, the standard value for ordinary glass. A higher refractive index gives a smaller critical angle, which is why diamond at 2.42 has a critical angle of only 24 degrees and traps light so effectively. Water, at 1.33, gives about 49 degrees.