Question

a) An object is placed 30 cm distance from the concave mirror and
image formed at 12 cm. from the pole. Find the focal length of the
mirror and mention the characteristics of the image formed.​

Answer 1

Answer:

-1/f =-1/u-1/v (- sign is because of sign convection)

= -1/30-1/12

=-7/60

=60/7

=8.57

Answer 2

The focal length of the mirror is (-20 cm) and formed image is virtual and erect.

Explanation:

Given that,

The object distance between the object and the concave mirror, u = 30 cm

Image formed at a distance of 12 cm from the pole, v = -12 cm

We need to find the focal length of the mirror. It can be calculated using mirror's formula such that :

$\dfrac{1}{f}=\dfrac{1}{v}-\dfrac{1}{u}$

$\dfrac{1}{f}=\dfrac{1}{(-12)}-\dfrac{1}{(-30)}$

f = -20 cm

So, the focal length of the mirror is (-20 cm). The ratio of image distance to the object distance is called magnification of the mirror. It is given by :

$m=\dfrac{-v}{u}$

$m=\dfrac{-(-12)}{(30)}$

m = 0.4

So, the formed image is virtual and erect. Hence, this is the required solution.

Learn more,

Mirror's formula

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