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Two plano-concave lenses of glass of re...

Two plano-concave lenses of glass of refractive index 1.5 have radii of curvature of 20 and 30 cm. They are placed in contact with curved surface towards each other and the space between them is filled with a liquid of refractive index `(4)/(3)`, find the focal length of the system.

A

48cm

B

72cm

C

12cm

D

24cm

Text Solution

Verified by Experts

The correct Answer is:
B
For diverging meniscus lens R(concave)ltR(convex)
`1/f=(mu-1)(1/R_(1) +1/R_(2)).1/u + 1/v=1/f`
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NARAYNA-RAY OPTICS AND OPTICAL INSTRAUMENTS -EXERCISE-2 (C.W)(REFRACTION THROUGH SPHERICAL SURFACES )
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