The figure shows initial positions of a source of light S and a light detector D. Both S and D move with velocity 10 cm s⁻¹, as shown. The converging lens of focal length 20 cm is fixed. Time instant(s) when the detector detects maximum intensity of light is/are :-

Question

G1 Physics · Accepted Answer

Derived solution: Step 1: Use the thin-lens formula 1/f = 1/v - 1/u with m = v/u. For lens material/medium changes use the lens-maker relation with the relative refractive index; powers of thin lenses in contact add. Step 2: Test each statement independently using these relations and the data/figure. Step 3: The statements that satisfy the required optical conditions are A: 3 sec; C: 6 sec. Hence the correct answer is A,C.