Question

If an object 70 millimeters high is placed 40 millimeters from a converging lens and the image is formed 120 millimeters in front of the lens on the same side as the object, what’s the height of the image?

Answer 1

The basic proportion we have to use is:

`d_o:d_i = h_o:h_i`
where
`d_o` is the distance of the object from the lens (40 mm),
`d_i` the distance of the image from the lens (120 mm),
`h_o` the height of the object (70 mm) and
`h_i` the height of the image (that we have to find). Solving for
`h_i` we find

`h_i = (d_i \cdot h_o)/(d_o) = ((120 mm)(70 mm))/(40 mm)=210 mm`
so, the height of the image is 210 mm.