A detailed and engaging lesson presentation (32 slides) and accompanying worksheet that goes over the rules of reflection and looks at the critical angle and how this is connected to total internal reflection. The lesson begins by focussing on the key terminology, such as the normal and incident ray so that students are able to label ray diagrams. Students then carry out a simple reflection investigation with a plane mirror so that they can see the rules of reflection and the connection between the angle of incidence and the angle of reflection. Moving forwards, students will be introduced to the term, critical angle, and how this is related to total internal reflection. A second practical is used to find the critical angle with light before a number of understanding checks are used which includes the students writing a letter to a patient explaining how an endoscopy works.