Question

The image of an object placed 15 cm from a concave mirror is formed at a distance of 30 cm from it. Calculate the possible focal length of the mirror from the this information​

Answer 1

Refer to the above attachment for full solution.

The required focal length is of -10 cm.

Answer 2

Answer:

-10 cm

Explanation:

Given that ,

u = -15 cm, v = -30 cm

To find :

f = ?

As per the mirror formula,

$\tt{\frac{1}{v} + \frac{1}{u} = \frac{1}{f}}$

$\tt {- \frac{1}{30} + ( - \frac{1}{15} ) = \frac{1}{f}}$

Finding out the L.C.M of 30 & 15 ,

$\tt{ \frac{ - 1 - 2}{30} = \frac{1}{f}}$

$\tt{- \frac{ 3}{30} = \frac{1}{f}}$

$\tt{ - \frac{ 1}{10} = \frac{1}{f}}$

Thus,

$\tt{f = - \frac{10}{1}}$

f = -10 cm

The possible focal length of the mirror from the this information is -10.