Question

Problem 3 A lens with a focal length of 5 meters is used to look at an object that is x meters away, find the image distance, magnification, and whether the image is inverted or upright for the following values of x: a) x = 15 meters b) x = 2 meters c) If the object is placed at 5 meters away, find the image distance only. d) If the image distance is 5 meters away, find the object distance only.

Answer 1

given that

focal length f = 5 m

a) if x = 15 m

from the relation

1/x+1/x' = 1/f

1/x' = 1/f-1/x

x'= xf/x-f

x' = 15*5/15-5 = 7.5 m = image distance

magnification m = -7.5/15 = -0.5

image is inverted

b) if x = 2 m

x' = 2*5/2-5 = 10/-3 = -3.33 m

magnification = 3.33/2 = 1.665

image is upright

c) if x = 5m

object is located at infinity

x' = imfinity

d) if x' = 5m

x = x*f/x'-f

x = infinity