ICSE Class 10 Physics 2020 Solved Paper

A lens of focal length $20 {\cm}$ forms an inverted image at a distance $60 {\cm}$ from the lens.

Question : 39 of 67

Marks: +1, -0

How far is the lens present in front of the object?

Solution:

Given :

f=+20 {\cm}, v=+60 {\cm}

We know,

\;{1}/{f}=\;{1}/{v}-\;{1}/{u}

⇒ \;\; \;{1}/{20}=\;{1}/{60}-\;{1}/{u}

⇒ \;\; \;{1}/{u}=\;{1}/{60}-\;{1}/{20}

⇒ \;\; \;{1}/{u}=\;{1-3}/{60}=\;{-2}/{60}

⇒ \;\; \;{1}/{u}=\;{-1}/{30}

\;\; u=-30 {\cm}

∴

The lens is present in front of the object at a distance of

30 {\cm}

from it.

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