Q4. Assertion: the object pin and the image pin must not be interchanged during the experiment. Reason: each pin has its own index correction. Are both true, and does the reason explain the assertion?
Both are true, and the reason explains the assertion (Laboratory Manual, Experiment 10, page 83).
Q5. In a convex-lens experiment the u–v hyperbola meets the line u = v at u = v = 30.0 cm. Find the focal length.
There u = v = 2f, so f = 15.0 cm (Laboratory Manual, Experiment 10, page 82).
Q6. A dentist uses a concave mirror to see a tooth. How does it help?
Held so that the tooth is closer than the focus, the mirror forms an erect, magnified, virtual image of it (Laboratory Manual, Experiment 9, page 76, Self assessment 1; reasoned from NCERT Exercise 9.15(d), page 250).
Q7. Why should the convex mirror in Experiment 11 preferably be front-coated?
A mirror coated at the back reflects from both the glass surface and the coating, giving multiple images that make removing parallax harder (Laboratory Manual, Experiment 11, page 90).