Question

a concave lens has a focal length of 10 cm where should the object be place to form a virtual image at a distance 30 cms from the lens


please answer this question ​

Answer 1

Answer:

The object should be placed 7.5 cm from the lens.

Explanation:

Given: Focal length(f) = -10 cm

           Image distance(v) = 30 cm

To find: Image distance(u)

Solution: By using lens formula = 1/f = 1/v - 1/u

               So, 1/u = 1/v - 1/f

                      1/u = 1/30 - 1/-10

                      1/u = -1-3/-30

                      1/u = -4/30

                        u = -7.5 cm

So, The object should be placed 7.5 cm from the lens.