Question

the image of an object formed by convex lens is of the same size as the object if the image is formed at a distance of 40 cm .find the focal length of the lens and also the power of the lens .at what distance from the lens is the object placed.

Answer 1

Image is formed at a point in the right side of the mirror. So the object is placed at a distance of 40cm from the lens.

So u = – 40cm

f = c / 2

= 40 / 2 = 20

Power = 1 / 20 cm = 1 / 0.20 m = 100 / 20 = + 5 D

Hope it helps!

Answer 2

Answer:

P = 4D

Explanation:

Same size of image is formed by a convex lens only when the object is placed at a distance u=2f from the optical center and image is also formed at distance 2f on other side of lens.

⟹2f=50

⟹f=25cm

P=f(m)1=0.251

⟹P=+4D