When at school, I laugh at the students who attempt to fix themselves through a school window. The window is two-way and yet students can see themselves in it without noticing the people behind it.
In this photo I am adjusting myself in a Castle Building window. The sun produced light which bent through the front doors then reflected off the floor. There was also light produced from the ceiling fixtures. This combination created a “mirror”. Reflection is possible because light hits the glass at a certain angle. Because of that special angle the window then acts like a planar mirror. The image created is virtual and same distant away from mirror to object. Sometimes the glass does not produce an image.
Mr. Snell had performed many experiments to develop a way to find the index of refraction. With this knowledge we know the index of refraction of glass, and this can determine the angle in which light is internally reflected. This angle is the same angle in which I could see myself in the picture.
I hope students are more aware that the windows are two-way and will steer clear from embarrassing motions in front of it.