Question

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

Answer 1

Answer:It is placed 50cm from the mirror.power of lens is 0.04

Explanation:this is because a convex mirror forms a real,inverted and same sized image when the object is placed at its centre of curvature which is 50cm.The power of the lens is the reciprocal of the focal length which is half the centre of curvature(50),hence it is 1 out of 25 =0.04

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 !!