Physics · Geometrical Optics

NEET (UG) 2023 — Question 40

Two thin lenses are of same focal lengths $(f)$ , but one is convex and the other one is concave. When they are placed in contact with each other, the equivalent focal length of the combination will be :

Option A:
$f / 4$
Option B:
$f / 2$
Option C:
Infinite
Correct
Option D:
zero

Answer: C

Step-by-step solution

Convex lens $f_1>0$ , concave lens $f_2<0$

\begin{aligned} & \frac{1}{f_{\mathrm{eq}}}=\frac{1}{f_1}+\frac{1}{f_2}=\frac{1}{f}-\frac{1}{f}=0 \\ & f_{\mathrm{eq}}=\infty \end{aligned}

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Exam: NEET (UG) 2023
Paper: 2023 paper
Subject: Physics
Chapter: Geometrical Optics
Topic: Lenses and Their Combinations, Silvering of Lens

Light travels a distance x in time t 1 in air and 10 x in time t 2 in another denser medium. What is the critical angle for this medium?
In the figure shown here, what is the equivalent focal length of the combination of lenses (Assume that all layers are thin)?

Answer: C

Step-by-step solution

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