A point object is placed at 30 cm from a convex glass lens …

Physics Ray Optics Concave and Convex Mirror/Lens and Focal Lenght MCQ (Single Correct)

A point object is placed at 30 cm from a convex glass lens of focal length 20 cm. The final image of object will be formed at infinity if -

Another concave lens of focal length 60 cm is placed in contact with the previous lens

Another convex lens of focal length 60 cm is placed at a distance of 30 cm from the first lens

The whole system is immersed in a liquid of refractive index 4/3

The whole system is immersed in a liquid of refractive index 9/8

Text Solution

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The correct answer is:

CHECK THE SOLUTION.

(a, d)

Final image is formed at infinity if the combined focal length of two lenses becomes 30 cm or

= + ⇒ f = – 60 cm

Similarly, let μ be the refractive index of liquid in which focal length of the given lens becomes 30 cm.

Then, = …(1)

⇒ = …(2)

solving (1) & (2), μ =

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