An optical arrangement consists of two concave mirrors M₁ and M₂, and a convex lens L with a common principal axis, as shown in the figure. The focal length of L is 10 cm. The radii of curvature of M₁ and M₂ are 20 cm and 24 cm, respectively. The distance between L and M₂ is 20 cm. A point object S is placed at the mid-point between L and M₂ on the axis. When the distance between L and M₁ is n/7 cm, one of the images coincides with S. The value of n 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 80 or 150 or 220. Therefore the correct option is C.