Question

one centimetre object is placed at a distance of 2f from a convex lens what is the height of the image formed

Answer 1

Using (1/ v) - (1/ u) = (1 / f)

(1/ v) - (1/ - 2f) = (1 / f)

(1/ v) = (1 / 2f)

v = 2 f

m = v / u = 1

h' / h = 1

h' = h = 1 cm
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Answer 2

As, height of image/height of object=image distance /object distance
..let height of image be x cm...
,so x/1=2f/2f/(by below)...so x=1cm is the height of image is correct
Here u=-2f ...v=?...focal lenghth for covex lens is +ve
so....1/v-1/u=1/f
1/v=1/f+1/(-2f)
=1/f-1/2f=1/2f.
so,v=2f