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 update also find the power of lens​

Answer 1

Answer:

Given,

v=50 (v is positive for real image )

u= -50

We know,

1/v- 1/u = 1/f

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

=>1/50 + 1/50 = 1/f

=>2/50 = 1/f

=> 1/25 = 1/f.

=> f =25cm [cross- multiplication]

=>f = 0.25m [ f is converted from 'cm to m ' because f should be in meter in case of power ]

Now,

P = 1/f

=> P = 1/ 0.25

=>P = 1÷ 25 /100

=>P = 100 / 25

=> P = 40D [ the unit of power is 'dioptre']

I hope this will be helpful for you

Thank you

Answer 2

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.