Where is a relection?

 

A text book will tell you that the reflection is the same distance behind the mirror as the image is in front of the mirror. This can be proven using ray diagrams. I always used to like to use a set up like the one above to use the partial reflection in a pane of glass. I used a safety screen so it was easy to measure in front and then push a ruler behind the reflection. Not so easy to do from the carriage at Bassenthwaite Lake Station!