Need physics help please?

Question

A small insect viewed through a convex lens is 1.2 cm from the lens and appears two times its actual size. What is the focal length of the lens?

Answer 1

By definition magnification of a lens is given as the ratio of object distance to image distance

From your question

The object distance is 1.2m

The magnification is 2

Therefore 2 = (1.2/image distance)

Image distance = (1.2/2) = 0.6 m

calculate the focal length from the formula f= (uv/v+u)= 0.4 m

Answer 2

1/Distance of object + 1/Distance of image = 1/Focal Length .

1/1.2 + 1/2x1.2 = 1/f

f = 0.8 cm

Answer 3

focal length =20 cm