Question

an object 4 cm high is placed at a distance of 10 cm from a convex lens of focal length 20 cm find the position, nature and size of the object​

Answer 1

The position of the image is left to that of the convex lens. It is virtual, erect and two times larger in size than the object.

Explanation:

Given that:

h = 4 cm

u = -10 cm (Object is at left side of lens)

f = 20 cm

Using the lens formula:

➡ 1/v - 1/u = 1/f

➡ 1/v - (-1/10) = 1/20

➡ 1/v + 1/10 = 1/20

➡ 1/v = 1/20 - 1/10

➡ 1/v = 1/20 -2/20

➡ 1/v= -1/20

⇒ v = -20 cm

We also know that, Magnification, m = v/u

= -20/-10 = 2

Also, m = h'/h

➡ 2 = h'/4

➡ h' = 4 x 2 = 8 cm