Question

A convex lens forms a real and inverted image of an object at a distance of 50cm from it. Where is object to be placed also find the power of lens.

Answer 1

Answer:

It is given that the image is formed at a distance of 50cm from the lens. And since the image is real, v = +50cm. This means that u = -50cm. Therefore, the needle must be placed at a distance of 50cm from the lens.

Explanation:

Image formed is real and inverted

∴ Magnifications (m) = -1

Since the image is real, image distance is a positive value.

Image distance (v) = 50 cm

Let the object distance be u

Magnification in a lens (m) = v/u

-1 = 50/u

u = -50 cm

The needle is placed 50 cm in front of the convex lens.

Need to find the focal length (f)

According to the lens formula,

1/f = 1/v – 1/u

1/f = 2/50

1/f = 1/25

f = 25cm

Power of the lens p = 1/f

P = 1/25cm-1

P = 1/25 × 10-2 m-1

P = 4m-1

Since 1m-1 = 1D

∴ P = 4D