If the image formed by a lens for all positions of an ...

CBSE Class 10 Science 2017 Outside Delhi Term II Set 1 Paper

Question : 16 of 36

Marks: +1, -0

If the image formed by a lens for all positions of an object placed in front of it is always erect and diminished, what is the nature of this lens? Draw a ray diagram to justify your answer. If the numerical value of the power of this lens is

10 {\D}

, what is its focal length in the Cartesian system ?

Solution:

It is a concave lens (diverging lens).

Power of a lens is given by the relation

\; {\P}\;=\;{1}/{f(\;\text " in metre "\;)}

∵ \; {\P}\;=10 {\D}

∴ \;f\;=\;{1}/{ {\P}}=\;{1}/{10}=0.1 {\m}

-10 {\cm}

, as lens is concave lens.

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