Prism — Deviation vs Incidence AngleHardQuestion 20259
Question
As angle of incidence on a prism increases from 0° to 90°, the angle of deviation:
- AContinuously decreases
- BContinuously increases
- CFirst decreases to a minimum value, then increasesCorrect
- DStays constant
Correct answer
First decreases to a minimum value, then increases
Explanation
The deviation-angle curve has a U-shape with a minimum at the angle of minimum deviation (symmetric passage). This is why the minimum deviation angle D_m is used in the prism formula: it's the unique configuration where deviation is least and the prism formula is simplest.