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 an object? also find the power of the lens

Answer 1

Explanation:

the image has been placed at 2f of lens

so our focal length = R/2 = f

50cm / 2 = 25cm

now by power of lens formula

we have

1/f (m)

100/25 = +4D ans..

Answer 2

$\mathfrak{\huge{\red{\underline{\underline{Answer :}}}}}$

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 !!