A thin equiconvex lens of refractive index ${\rm{3}}\,{\rm{/}}\,{\rm{2}}$ and radius of curvature ${\rm{30}}\,\,{\rm{m}}$ is put in water (refractive index $ = \frac{4}{3}\,)$. Its focal length is

${\rm{1}}{\rm{.20}}\,\,{\rm{m}}$

${\rm{0}}{\rm{.15}}\,\,{\rm{m}}$

${\rm{0}}{\rm{.30}}\,\,{\rm{m}}$

${\rm{0}}{\rm{.45}}\,\,{\rm{m}}$

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NEET UG PHYSICS MCQ: RAY OPTICS

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Application +4 | -1

A thin equiconvex lens of refractive index

\mathrm{3}\,\mathrm{/}\,\mathrm{2}

and radius of curvature

\mathrm{30}\,\,\mathrm{m}

is put in water (refractive index

= \frac{4}{3}\,)

. Its focal length is

View answer and explanation

Correct option: D

\mathrm{1}\mathrm{.20}\,\,\mathrm{m}

Option D (

\mathrm{1}\mathrm{.20}\,\mathrm{m}

) is correct because the focal length of the lens changes when immersed in water due to the change in refractive index of the surrounding medium, as calculated by the lens maker's formula.

More Questions from RAY OPTICS

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An object 5 cm tall is placed

\mathrm{1}\,\,\mathrm{m}

from a concave spherical mirror which has a radius of curvature of

\mathrm{20}\,\,\,\mathrm{cm}

. The size of the image is Red colour is used for danger signals because A ray of light is incident on the hypotenuse of a right-angled prism after travelling parallel to the base inside the prism. If

\mathrm{\mu }

is the refractive index of the material of the prism, the maximum value of the base angle for which light is totally reflected from the hypotenuse is Statement-A: The minimum distance between an object and its real image formed by a convex lens is

2{f}

.

Statement-B: The distance between an object and its real image is minimum when its magnification is -1. Assertion: We cannot produce a real image by plane or convex mirrors under any circumstances.
Reason: The focal length of a convex mirror is always taken negative. If both the object and image are at infinite distance from a refracting telescope its magnifying power will be equal to