Question

A needle of size 5 cm is placed 45 cm from a lens produced an image on a screen placed 90 cm away from the lens.

Answer 1

(i) Identify the types of lens. 

Calculate focal length of the lens. 

Height of the object h₁ = 5 cm 

Distance of the object u = -45 cm 

Distance of the image v = 90 cm 

We know that

Focal length of the lens = 30 cm 

Since focal length is positive the lens is convex lens.

(ii) Identify the size of the image

∴ h₂ = -10 cm

The negative sign indicates that the image is real and inverted.