Question

An object is placed at a distance of 40 cm infront of a convex lens of focal length 20 cm the image is formed at which distance

Answer 1

Object-distance = u = -40 cm
Focal-length = f = +20 cm
Image-distance = v = ?


By lens formula ,
1/v - 1/u = 1/f
i.e., 1/v = 1/f + 1/u
= 1/+20 + 1/(-40)
= 1/20 - 1/40
= 20/800
= 1/+40

Thus , v = +40
i.e., the image is formed 40 cm on the other side of the lens .
:)

Answer 2

Answer:

hiii

Explanation:

object distance , u = - 40 cm

focal length , f = 20 cm

size of object , b1 = 8 cm

we know that

1/ f = 1 / v - 1/ u

1/ 20 = 1/ v - 1/-40

1/v = 1/20 - 1/40

v = 40 cm

thus image distance , v = 40 cm

b2 / b1 = v/ u

b2 = 40 /-40× b1

40/-40×8

=-8 cm

this is your ans. I hope it helps you