Question

the focal length of a concave lens is 30 cm at what distance should an object be placed from the lens so that it forms an image at 20 centimetre from the lens​

Answer 1

Hey ✌..

Required solution..

1. 1/u=1/v -1/f

          = -1/15 +1/20

          =-4+3/60

           =-1/60

u=-60cm

H=v/u *h

 =-15/-60 * 5

=+1.25 cm

__________________

2. 1/u =1/v-1/f

          =1/60 -1/30

          = 1-2/60

           =-1/60

u= -60cm

m=v/u

m=60/-60

m=-1

hope this will help you...

Ples mark brainliest ☺