Question

a concave lens of focal length 15cm forms an image10cm from the lens.how far is the object placed from the lens ?Draw the ray diagram

Answer 1

$\bold{CONCAVE \: LENS}$

A convex lens is thick at its periphery and thin in the middle.It diverges the rays of ligh that incident
upon it. It is also called diverging lens.


$\bold{GIVEN}$

Focal length f= 15cm

Image distance v = 10 cm

By lens formula we know,

$\huge \boxed{ \dfrac{1}{f} = \dfrac{1}{v} + \dfrac{1}{u}}$

$\mathsf{ \dfrac{1}{-15} = \dfrac{1}{-10} + \dfrac{1}{u}}$

$\mathsf{ \dfrac{1}{u} = \dfrac{1}{15} + \dfrac{1}{-10}}$

$\mathsf{ \dfrac{1}{u} = \dfrac{1}{15} - \dfrac{1}{10}}$

$\mathsf{ \dfrac{1}{u} = \dfrac{2- 1}{30}}$

$\mathsf{ \dfrac{1}{u} = \dfrac{1}{30}}$

$\huge \boxed{\mathsf{ u = 30}}$