Question

The image of an object place at 60 cm in front of a lens is obtained on a screen at a distance of 120 cm from it. Find the focal length of the lens. What would be the lens? What would be the height of the image? If the object is 5 cm high?

Answer 1

Explanation:

Object distance u = -60 cm

Image distance v = +120 cm

Using lens formula, 1/f = 1/v - 1/u

1/f = 1/120 - ( -1/60 ) = 1/120 + 1/60 = 3/120 = 40 

f = +40 cm

H(image) / H(object) = v/u

Hi = -120/60 X 5 = -10 cm