Question

A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it.Where is the needle placed in front of the convex lens if the image is equal to the size of the object? also, find the power of the lens

Answer 1

as it forms equal size image it should be placed on center of curvature.inthis case image distance should be equal to object distance. and if we use lens formula we get focal lenght as 100 cm.so power will be 1 diapter

Answer 2

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The position of the image should be at 2F since the image is the real and same size.

It is given that the image of the needle is formed at a distance of 50 cm from the convex lens. Therefore, the needle is placed in front of the lens at a distance of 50 cm.

Object distance (u) = – 50 cm

Image distance, (v) = 50 cm

Focal length = ( f )

According to the lens formula,

$\frac{1}{v} - \frac{1}{u } = \frac{1}{f}$

$\frac{1}{f} = \frac{1}{50} - \frac{1}{ - 50}$

$= > \frac{1}{50} + \frac{1}{50} = \frac{1}{25}$

$f = 25cm \: = 0.25m \:$

$power \: of \: lens \: = \frac{1}{f(in \: metres \: )} = \frac{1}{0.25} = \: + 4d$

Hope it Helps !!