Question

Magnifica tion of an object for a spherical mirror is +2.5, calculate the focal length of the mirror if the object is 6cm from the mirror.

Answer 1

Answer:

focal length = 10

Explanation:

Given:

magnification = 2.5

object distance u = -6cm

$M = - \frac{v}{u}$

$v = - M \times u$

$v = - 2.5 \times - 6 = 15cm$

Focal length can be calculated by Mirror formula,

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

$\frac{1}{f} = \frac{1}{15} + \frac{1}{ - 6}$

$\frac{1}{f} = \frac{1}{15} - \frac{1}{6}$

$\frac{1}{f} = \frac{1 \times 2}{15 \times 2} - \frac{1 \times 5}{6 \times 5} = \frac{2}{30} - \frac{5}{30} = \frac{2 - 5}{30} = - \frac{3}{30} = - \frac{1}{10}$

$f = - 10$

Therefore focal length is 10 and negative sign indicates that it is concave mirror