Question

a real image of an object placed at a distance of 20cm concave mirror infront fromed at distance of 30cm from the mirror find focal length

Answer 1

distance of the object from the mirror
u = -20 cm
and image distance
v = 30 cm
now by mirror formula 1
1/v +1/u =1/f
1/30 + 1/(-20)
1/30 - 1/20
(2- 3)/60
-1/60 = 1/f
hence focal length is - 60 cm

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