Question

A 4.0 cm tall object is placed 8 cm in front of a double-convex lens (n = 1.52). The height of the image is y'- 7.0 cm. Based on this information find: a) The magnification, m. b) The image distance, s'. c) The focal length of this lens, f.

Answer 1

Here we have given that,

Ho = 4 cm

Hi = y' = 7 cm

U = 8 cm

n = 1.52

a)

Magnification will be given as

m = - Ho/Hi = 7/4 = -1.75

b)

Also from the magnification relation we have,

m = 1.75 = V/U

v = s = 1.75×8 = 14 cm

c)

Focal length will ve given as,

f = V×U/U-V = -14×8/-8-14 = 5.0909 cm

Which is our required focal length of the lense.