We have been investigating how light travels in straight lines using torches and mirrors. We then had lots of fun working in groups to make a periscope. A periscope is an optical instrument that uses mirrors to reflect images through a 3D shape. Light rays hit the top mirror and are then reflected at an angle of 90 degrees down the periscope to the second mirror. At the bottom of the periscope, the light hits another mirror and is then reflected into the viewer's eye.