Question

a concave lens of the focal lenght 12 cm forms an image at 10cm from the lens .how far is the object placed from lens

Answer 1

Focal length ,f = - 12cm

Image distance,v = - 10cm

Object distance u = ?

From lens formula

1/v - 1/u = 1/f

So,

1/-10 - 1/u = 1/-12

1/u = 1/(-10) + 1/12

1/u = -6+5 /-60

=6-5/60

=1/-60

u = - 60cm

Thus object is placed 60 cm away from the concave lens.

Negative sign shows that object is at 60cm in front of the lens.

Therefore u = -60 cm