An object placed 20 cm in front of a mirror is found to have an image 15 cm
(a) in front of it,
(b) behind the mirror.
Find the focal length of the mirror and the kind of mirror in each case.
Object distance, u = -20cm
(a) Image distance = -15 cm
Using the mirror formula, we get
focal length= 
cm
The kind of mirror is concave mirror.
(b) Image distance = 15cm
Using the mirror formula, we get
focal length = 60 c-m
The kind of mirror is convex mirror.
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