Q4. Assertion: the minimum of the i–δ curve is hard to locate exactly. Reason: near the minimum the deviation changes very little as i changes. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion; that is why extra readings are taken near the minimum (Laboratory Manual, Experiment 13, page 103).
Q5. If the experiment were done with each angle of emergence used as the angle of incidence, would the graph change?
No: tracing a ray backwards swaps i and e and gives the same deviation, so each new point (e, δ) lies on the same curve (Laboratory Manual, page 103, Self assessment 2; reasoned from NCERT pages 239–240).
Q6. A prism of angle 60° gives Dm = 40°. Find the angle of incidence at minimum deviation and the refractive index.
i = (A + Dm)/2 = 50°, and n = sin 50°/sin 30° ≈ 1.53 (NCERT Eqs. (9.37)–(9.38), page 240).
Q7. What advantage of the minimum-deviation position does the Laboratory Manual give?
In the Laboratory Manual’s words, “the image is brightest in this position” (page 100); give that in an exam. Strictly, brightness depends on the optical conditions and is not a universal test (reasoned). Also, the flat minimum (page 103) means a small error in i hardly changes δ, although the flatness also makes the exact incidence angle of the minimum hard to locate (reasoned).