A rod of length 2 cm makes an angle 2π/3 rad with the principal axis of a thin convex lens. The lens has focal length 10 cm and is placed at a distance 40/3 cm from the object, as shown. The image height is 30√3/13 cm and it makes an angle α with the principal axis. If α = π/n rad, find n.

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: Substitute the values given in the question and apply the geometry/sign convention shown. Step 3: On simplification the result is 6. Therefore the correct option is A.