Two convex lenses of focal length f and 2f are arranged to have their foci at the same point as shown in the figure. A beam of parallel light of diameter 1 cm is incident into the first lens. The beam emerging from the second lens is:

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 parallel, of diameter 2 cm. Therefore the correct option is D.