Question

At what distance from a convex lens of focal length 30cm, an object should be placed, so that the size of the image be half of the object?

Answer 1

use Lens formula,

1/v - 1/u = 1/f

where,

v = image distance from lens

u = object distance from lens

f = focal length

here ,

f = 30 cm { for convex lens f is positive }

v = 60cm

now,

1/60 - 1/u = 1/30

1/60 - 1/30 = 1/u

-1/60 = 1/u

u = -60 cm

hence, object distance also 60cm but left side of convex lens . in which position of image is right side.

now,

magnification = ( image distance )/(object distance ) = 60/(-60) = -1

magnification = -1

it means height of image = height of object . but both lies just opposite sides of lens .

Answer 2

Answer:

-60cm

Explanation:

let v = 60cm

Hope it helps you