Question

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

Answer 1

It is given that the image of the needle is formed at a distance of 50 cm from the convex 
lens. Hence, 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,

Answer 2

Hey Happy Soul ❤

Your Answer :

The position of image should be at 2F, since the image is 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.

Focal length :

Object distance (u) = - 50 cm

Image distance, (v) = 50 cm

Focal length = f

According to the lens formula,

1/v - 1/u = 1/f

1/f = 1/50 - 1/(-50)

1/f = 1/50 + 1/50

1/f = 1/25

f = 25 cm = 0.25 m

Power of lens :

p = 1 / f ( in meter)

p = 1/0.25 = +4 D

Hope this will helps you ☺

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