Question

an object is placed at a distance of 15 cm from a concave mirror a real image is formed at distance of 25cm find focal length of mirror​

Answer 1

Given:

Object distance(u)=15cm(negative)

Image distance(v)=25cm(negative)

let focal length be =f(negative)

By lens Formula,

1/v+1/u=1/f

=>1/-15-1/25=1/-f

Hey calculate urself now

Answer 2

Answer :-

The focal length of the mirror is -9.375 cm.

Explanation :-

Given,

• u = -15 cm
• v = -25 cm
• f = ?

Using mirror formula,

$\frac{1}{f} = \frac{1}{v} + \frac{1}{u} \\ \frac{1}{f} = \frac{ - 1}{25} + ( \frac{ - 1}{15} ) \\ \frac{1}{f} = \frac{ - 1}{25} - \frac{1}{15} \\ \frac{1}{f} = \frac{ - 3 - 5}{75} \\ \frac{1}{f} = \frac{ - 8}{75} \\ f = \frac{ - 75}{8} \\ f = - 9.375 \: cm$

Hence, focal length of the mirror is -9.375 cm.