Question

Find out how far should an object be placed from a convex lens of focal length 30 cm to obtain an image on a screen kept at 40 cm from a lens also find height of image if height of object is 10 cm

Answer 1

I think so.. it is correct!

Answer 2

Length of the object or its height = 10cm
Focal length of the object = 30cm
Distance of the image from the lens = 40cm
1/f = 1/v - 1/u
1/30= 1/40- 1/u
1/u = 1/40 - 1/30
1/u = 3-4/120
U => 120 (convex lens)

Hope it will help you