Question

The adjacent figure shows a thin plano-convex lens of refractive index μ₁ and a thin plano-concave lens of refractive index μ₂ , both having same radius of curvature R of their curved surfaces. The thin lens of refractive index μ₃ has radius of curvature R of both its surfaces. This lens is so placed in between the plano-convex and plano-concave lenses that the plane surfaces are parallel to each other. The focal length of the combination is

(A) R/(μ₁ + μ₂ - μ₃ - 1)

(B) R/(μ₁ + μ₂ + μ₃)

(C) R/(μ₁ - μ₂)

(D) R/(μ₁ - μ₂ - μ₃ - 3)

Answer 1

Correct Answer is: (C) R/(μ₁ - μ₂)