Question

The owner of a van installs a rear-window lens that has a focal length of -0.300 m. When the owner looks out through the lens at an object located directly behind the van, the object appears to be 0.250 m from the back of the van, and appears to be 0.350 m tall. (a) How far from the van is the object actually located, and (b) how tall is the object?

Answer 1

Answer:

a) o =  -0.136 m , b)   h = 0.643 m

Explanation:

For this problem we will use the constructor equation

          1 / f = 1 / o + 1 / i

Where f is the focal length, "o and i" are the distance to the object and the image, respectively

         1 / o = 1 / f  - 1 / i

         1 / o = -1 / 0.300  - 1 / 0.250

         1 / o = -7.33

         o =  -0.136 m

The magnification is given by the expression, we must be careful with the signs

         m = h’/ h = - i / o

         h = - h ’o / i

         h = - 0.350 0.250 / (- 0.136)

         h = 0.643 m