Question

An object placed 45 cm from a lens forms an image on a screen place 90 cm on the other side of the lens. Identify the type of the lens and find its focal length.

Answer 1

Answer:

The lens is a biconvex lens. Image is inverted and magnified. Focal length is 90 cm.

Explanation:

u= -45cm

v= 90cm

using: 1/f= 1/v - 1/u, we get f=90cm

Answer 2

Answer:

30cm

Explanation:

given:

object distance,u=-45cm

lmage distance ,v=90cm

using lens formula

1/f=1/v-1/u

=1/90-(-1/45)

f=+30cm

lt 's focal length is positive, so

it is a convex lens