Question

2. A 10 mm long awl pin is placed vertically in front of a concave mirror. A 5 mm long image of the awl pin is formed at 30 cm in front of the mirror. The focal length of this mirror is_________________​

Answer 1

Answer:

The focal length of the concave mirror can be formed by the formula

1/ f 1/v + 1/u

Where f= focal length of the mirror v-distance of the image from the pole u-Distance of the object from the pole In the above question, it is given that the image is formed in front of the mirror, so the image is

real and is at a distance of 30 cm from the pole

Therefore, v = -30 cm

Also, we are given with the image height aswell as the object height.

.. We will calculate the magnifying factor as

m= - y/x

m = - 5/10

also m= u/v

m= -30/u = - 1/2

u = 60 cm

It should be noted that the object distance is

always negative, so u = -60 cm

So, the focal length of the concave mirror is calculated by the formula

1/f =1/v +1/u

1/f = - 1/30 - 1/60

1f = - 90/1800

f = -20 cm

The focal length of the concave mirror is always negative as it is clear from the value obtained above. So, the magnitude of the focal length of the mirror is 20 cm.

EXPLAIN

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