Question

A concave lens has a focal length 30 cm. Find the position and magnification (m) of the image for an object placed in front of it at distance 30 cm. State whether the image is real or virtual?

Answer 1

Object distance = -30cm

Focal length = f = -30cm

Image distance = v = ?

`1/"v" - 1/-30 = 1/-30`

`1/"v" = - 1/-30 - 1/30`

`1/"v" = -2/30`

`1/"v" = - 1/15`

v = - 15

m = `"v"/"u"`

m = `(-15)/-30 = 0.5` 

Here image formed is virtual and erect.