KVPY SA Exam 2014 Question Paper

Question : 23 of 80

Marks: +1, -0

A concave lens made of material of refractive index 1.6 is immersed in a medium of refractive index 2.0. The two surfaces of the concave lens have the same radius of curvature 0.2 m. The lens w ill behave as a

divergent lens of focal length 0.4 m.
divergent lens of focal length 0.5 m.
convergent lens of focal length 0.4 m.
convergent fens of focal length 0.5 m.

Validate

Solution:

1/\f=[{1.6-2}/2][1/{-0.2}-1/0.2]

⇒

(-0.4)/2×2/(-0.2)

1/\f=2/1

f = 0.5 metre
Converging lens as f is positive.

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