Question

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. What is the focal length of te mirror ?​

Answer 1

Answer:

60

Explanation:

a/c question u got first magnifiaction =(-v/u=-1/2)

then u should apply magnifiaction =-v/u...where v given=30..from here u got u=-60.then apply mirror formula...1/v+1/u=1/f...where v=30and u=-60

Answer 2

HOPE IT HELPS :

Given :

Height of object ( ho )= 10 mm

V = -30 cm

Height of image ( hi )= 5 mm

Magnification = hi/ho

Magnification = 5 / 10

m = 1/2

Also magnification = -v / u

m = -v/u

1/2 = - v / u

u = -2v

Using Mirror Formula :

1 / f = 1 / v + 1 / u

1 / f = 1 / v - 1/2v

1 / f = 1 / 2v

Reciprocaling both sides

f = 2v

Hence focal length of mirror = - 60 cm

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