Acamera with a 50.0 mm focal length lens is being used to photograph a person standing 3.00 m away. (a) (6 points) how far from the lens must the film be? (b) (6 points) if you were taking a picture of a 1.75 m tall person how tall will the image be?

Explanation:

Given

object distance u = 3 m (- ve)

Focal length f = .05 m ( + ve )

Lens formula ,

1 / v - 1 / u = 1 / f

1 / v  + 1/3 = 1 / .05

1 / v =  1 / .05 - 1 / 3

1 / v = 20 -0 .333

= 19.667

v = 1 /19.667

v = .05 m = 5 cm.  

magnification = v / u = .05 / 3

size of image = ( .05 / 3) x 1.75 = 2.9 cm.