Plane (flat) mirrors have a reflective surface that bounces backlight off the mirror. We use these mirrors every day in our bathrooms, bedrooms, and cars. When you look in a plane mirror, you see a mirror image that is flipped backward and opposite to the objects, it is reflecting. Plane mirror is also used in Periscope. A periscope is an instrument used to observe something from a concealed position. Periscope is used by troops fighting in World War 1, they could see out of their trenches and not put their lives at risk by lifting their heads in front of an enemy. This simple form is also used to peek around a corner to view wildlife, or to look over a crowd of taller people at an event.