To explore the nature of reflection and how it enables us to see, get students to do Activity 3, Light Box. The angle of incidence (i) is the angle between the incident ray and normal the angle of reflection (r) is the angle between the reflected ray and normal.įigure 1 Reflection of light off a mirror, with incident (I) and reflected (R) rays and the angles of incidence (i) and reflection (r). where I is the incident (incoming) ray R is the reflected ray N is the normal line, which is an imaginary line that is perpendicular to the surface the light reflects off (a mirror in this case). This is easily demonstrated with a laser light, a mirror and a protractor to measure angles. Or in more mathematical terms the angle of incidence (i) is equal to the angle of reflection (r). Essentially, if light hits a mirror at one angle it will be reflected from the mirror at the same angle. The way light reflects off a surface is predictable and follows the law of reflection. This finding enabled him to conclude that rather than light emanating from the eye, it is reflected off objects in a straight line.
When he removed one lantern, the light spot that corresponded to that lantern disappeared. In the wall of the dark room he saw two light spots. A key difference with Ibn al Haytham’s conclusion was that he determined it by performing an actual scientific experiment where he shone two lanterns through two pin holes at different heights into a dark room. 9, identified the optical components of the human eye and correctly described vision as a process involving light rays bouncing from an object to a person’s eye. Abu Ali Mohammed Ibn Al Hasn Ibn Al Haytham (Ibn al-Haytham), who lived in present-day Iraq between A.D. Epicurus was honing in on the correct idea, but it took until the 9 th and 10 th centuries before we started to get close to what really happens. 300 BCE) that suggested light is emitted by sources other than the eye or the object itself and that vision is produced when light reflects off objects and enters the eye. It was the Greek philosopher, Epicurus ( c. Other Greek philosophers - most notably Euclid and Ptolemy - used ray diagrams quite successfully to show how light bounces off a smooth surface or changes direction as it passes from one transparent medium to another. Epicurus argued the opposite: Objects produce light rays, which then travel to the eye. Pythagoras (about 500 years BCE), best known for the theorem of the right-angled triangle, proposed that vision resulted from light rays emerging from a person’s eye and striking an object. But we didn’t always understand it this way. We can see objects because light reflects off that object and into our eyes.
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