Question

An object is placed at a distance of 20cm from the optical centre of a convex lens of focal length 15cm .find the distance of the image from the lens what will be the height of the image if the object is 4cm tall

Answer 1

Use the lens form:

1/f=1/v-1/u

1/30=1/v-(1/-20)

1/30=1/v+1/20

1/30-1/20=1/v

2-3/60=1/v

-1/60=1/v ;;;v = -60 cm

m = h of image/h of object = v/u

H/2 = -60/-20

H = 3*2

H = 6 cm