Question

A 2 cm high object is placed at a distance of 12cm from a convex lens perpendicular to its principal axis. the lens forms a real image whose size is 1.5 cm . find the power of the lens

Answer 1

Answer:

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Answer 2

Height of Object = ho = 2 cm

Object distance = u = -30 cm (negative sign shows object is in the same side of the mirror).

Height of Image = hi = 1.5 cm

Now,

m = -v/u = hi/ho

-v = 1.5×(-12)/2

v = 9 cm

By Mirror Formula,

1/v + 1/u = 1/f

1/9 - 1/12 = 1/f

4-3/36 = 1/f

f = 36 cm

f = 0.36 m

Now,

Power = P = 1/f(in m)

P = 1/0.36 D

P = 2.7 D