A concave lens has focal length of 20 cm. At what distance from the lens a 5 cm tall object be placed so that it forms an image at 15 cm from the lens? Also calculate the size of the image formed.

Question

Philoid · Accepted Answer

According to the question;

Object distance = u;

Image distance (v) = -15cm;

Focal length = -20cm

By lens formula;

⇒ u = -60cm.

Therefore, object is placed at 60 cm in front of lens.

Now;

Height of object h₁= 5cm;

Magnification = =

Putting values of v and u

Magnification =

⇒

Height of image is 1.25 cm.

Positive sign means image is virtual.