Question

A convex lens forms a image of a needle at a distance of 50cm. from lens FIND
a. where the needle is placed in front of convex lens,if the image is equal to the size of the object.
b. Find the nature of the image.
c. Find the power of lens​​

Answer 1

Explanation:

a)Object distance, u= – 50 cm

Image distance, v= 50 cm

Focal length = f

According to the lens formula,

u = -50 cm

v = + 50 cm.

f =?

1/f = 1/v – 1/u

1/f = 2/50 = 1/25

f = 25cm

b)If the image is formed at the same side as object, then it is real image. ...

If the size of image is smaller/bigger than object, then we say that image is diminished/enlarged respectively.

c)Power of the lens p = 1/f

P = 1/25cm-1

= 1/25(10-2m)-1

=100/25m-1 = 4m-1

1m-1 = 1D

P = 4D

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