SATHEE: ray-optics-and-optical-instruments Question 4

Ray Optics And Optical Instruments

ray-optics-and-optical-instruments Question 4

Question: Q. 5. The radius of curvature of the curved surface of a planoconvex lens is $20 cm$ . If the refractive index of the material of the lens be 1.5 , it will

(a) act as a convex lens only for the objects that lie on its curved side.

(b) act as a concave lens for the objects that lie on its curved side.

(d) act as a concave lens irrespective of side on which the object lies. [NCERT Exemplar]

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Solution:

Ans. Correct option : (c)

Explanation: As we know the relations between $f, μ, R_{1}$ and $R_{2}$ is known as lens maker’s formula :

$\begin{aligned} \frac{1}{f} = (μ - 1) (\frac{1}{R_{1}} - \frac{1}{R_{2}}) & R_{1} = \infty, R_{2} = - R & f = \frac{R}{(μ - 1)} \end{aligned}$

Given that,

$\begin{aligned} R & = 20 cm, μ & = 1.5 f & = \frac{R}{μ - 1} = \frac{20}{15 - 1} = 40 cm \end{aligned}$

Put the values;

As $f > 0$ , it means converging nature of the lens.

So, lens act as a convex lens irrespective of the side on which the object lies.

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Ray Optics And Optical Instruments

ray-optics-and-optical-instruments Question 4

Very Short Answertype Questions

Table of Contents

Engineering Preparation

Medical Preparation

NCERT Books & Solutions

Important Resources

Other Resources

Syllabus

Test Platform

Sample Mock Test

Mentorship

NCERT Exercise Video Solution

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