Question

A 3cm tall object is placed at a distance of 18cm in front of a concave mirror of focal length 12cm.find the position,nature and size of the image formed.
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Answer 1

Explanation:

given, height of object,h = 3 cm

object distance,u = -18 cm (since concave mirror)

focal length,f = -12 cm

now, using the formula

1/u + 1/v = 1/f

1/-18 + 1/ v = 1/-12

1/v= 1/18+1/-12

1/v= (2+3)/36

1/v= 5/36

v= 36/5

v= 7.2

hence, image distance is 7.2 cm

and it will form back side of the concave mirror

now magnification

m= h'/h

or m=-v/u

then we have h'/h= -v/u

h'/3=-(36/5)/(-18)

= 36/5 * 1/18

= 2/5 * 1

5h'= 6

h' = 6/5

h' = 1.2cm

hence we can conclude that the image will be 1.2 cm bigger than the object