JEE Main · 2022 · 28 Jul 2022 · Shift 2 · Geometrical Optics

In an experiment with a convex lens, the plot of the image distance (

v^{'}

) against the object distance (

u^{'}

) measured from the focus gives a curve

v^{'} u^{'} = 225

. If all the distances are measured in cm, the magnitude of the focal length of the lens is ____ cm.

Answer: 15

Solution

Newton's formula for a lens states that

v u = f^{2}

, where

v

and

u

are distances measured from the focal points. Given

v^{'} u^{'} = 225

, we have

f^{2} = 225

, so

f = 15

cm.

JEE Main · 2022 · 28 Jul 2022 · Shift 2 · Integer answer

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