TS EAMCET · Physics · Ray Optics
The two surfaces of a biconvex lens has same radii of curvatures. This lens is made of glass of refractive index 1.5 and has a focal length \(10 \mathrm{~cm}\) in air. The lens is cut into two equal halves along a plane perpendicular to its principal axis to yield two plano-convex lenses. The two pieces are glued such that the convex surfaces touch each other. If this combination lens is immersed in water (refractive index \(=\) \(4 / 3\) ), its focal length (in \(\mathrm{cm}\) ) is :
- A 5
- B 10
- C 20
- D 40
Answer & Solution
Correct Answer
(D) 40
Step-by-step Solution
Detailed explanation
If \(a\) lens of focal length \(f\) is divided into two equal parts as shown in figure (1) and each has a focal length \(f^{\prime}\) then \(\frac{1}{f}=\frac{1}{f^{\prime}}+\frac{1}{f^{\prime}} \quad \text { i.e., } f^{\prime}=2 f\) i.e., each part will have focal length…
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