Question: A concave lens forms the image of an object such that the distance between object and image is 10 cm...

Question

A concave lens forms the image of an object such that the distance between object and image is 10 cm and the magnification produced is $\frac { 1 } { 4 }$ . The focal length of the lens will be –

Answer 1

Solution

Concave lens forms virtual image of real object. So

u = – 4x; v = – x

\ Distance between object and image is

3x = 10 cm

\ u = – $\frac { 40 } { 3 }$ , v = – $\frac { 10 } { 3 }$ cm

\ $\frac { 1 } { \mathrm { f } }$ = $\frac { 1 } { - 10 / 3 }$ – $\frac { 1 } { - 40 / 3 }$

\ f = – 4.4 cm