Question

A 10mm long awl pin is placed vertically in front of a concave mirror . A 5mm long time of the awl pin in formed at 30cm in front of to mirror . The focal length of the mirror is u=60

Answer 1

Answer:

answer is - 20 and due to sign convention it will became negative..

Explanation:

Apply the relation – (v / u) = m = hi / ho as

= (- 5) / 10

= – {(- 30) / u}

=u = – 60 cm

Apply mirror formula as

= (1 / v) + (1 / u)= 1 / f

= 1 / (- 60) + 1 / (- 30)= 1 / f

= 1 / (- 20) = 1 / f or f = – 20 cm

so, -20 cm is the answer. The focal length lies in front of the mirror. Therefore, the sign is negative.

Answer 2

Answer:

m= h'/h= -v/u

5/10=-30/u

u=-300/5

u=-60cm

1/f=1/v+1/u

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

1/f = -2-1/60

1/f=-3/60

1/f=-1/20

f=-20cm

Therefore the focal length of the concave mirror is 20 cm front of the mirror

Explanation:

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