QJEEM23Ph08b0: JEE Main 2023 Physics - Class 12 JEEM23Ph08b0 Solution: A convex lens of refractive index 1.5 and focal length 18cm in…

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QJEEM23Ph08b0: JEE Main 2023 Physics - Class 12 JEEM23Ph08b0 Solution: A convex lens of refractive index 1.5 and focal length 18cm in…

A convex lens of refractive index 1.5 and focal length 18cm in air is immersed in water. The change in focal length of the lens will be ___________ cm.

(Given refractive index of water $= \frac{4}{3}$ )

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Accepted Answer

From lens makers formula

\frac{1}{f} = (\frac{μ_{lens}}{μ_{mrdium}} - 1) [\frac{1}{R_{1}} - \frac{1}{R_{2}}]

when in air

\frac{1}{18} = (\frac{1.5}{1} - 1) [\frac{1}{R_{1}} - \frac{1}{R_{2}}] . . . (1)

\mu_{\text {lense }}=1.5, \mu_{\text {air }}=1

.

when in water

\frac{1}{f} = (\frac{1.5}{4 / 3} - 1) [\frac{1}{R_{1}} - \frac{1}{R_{2}}] . . . (2)

from (1) & (2)

f=72

Change in focal length

=72-18 = 54

QJEEM23Ph08b0: JEE Main 2023 Physics - Class 12 JEEM23Ph08b0 Solution: A convex lens of refractive index 1.5 and focal length 18cm in…

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