Question

A 5 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 20 cm. The distance of the object from the lens is 30cm. Find the nature, position and size of the image

Answer 1

u=30cm
f=20cm
h of object=5cm
1/v=1/f+1/u
=1/20+1/30
=60/5
v=12cm
m=v/u=6/15

Answer 2

Height of object = 5cm

f = 20cm

u = -30cm

v = ?    

height of object = ?

nature of image = ?

By lens formula,

1/v - 1/u = 1/f

1/v - 1/-30 = 1/20

1/v + 1/30 = 1/20

1/v = 1/20 - 1/30

1/v = 1/60

v = 60cm

m = -v/u

m = height of image/height of object

v/u = height of image/height of object

60/-30 = height of image/5

(-2) (5) = height of image

-10cm = height of image

nature = real, inverted and magnified