1.2) Properties of light3) Theories about light

2. Light travels in straight lines:Las e r 3. Light travels VERY FAST around300,000 kilometres per second.At this speed it cango around the world 8times in one second. 4. Light travels much faster than sound. For example:2) Thunder and lightning start at the same time, but we will see the lightning first.2) When a starting pistol is fired we see the smoke first and then hear the bang. 5. We see things because they reflect lightinto our eyes: Homework 6. Luminous and non-luminous objects A luminous object is one that produces light.A non-luminous object is one that reflects light.Luminous objects Reflectors 7. ShadowsShadows are places where light is blocked:Rays of light 8. Light travels in straight lines Light travels much faster than sound We see things because they reflect light into our eyes Shadows are formed when light is blocked by an object 9. Aristotle (384 - 322 B.C.), an ancient Greek thinker, thought thatwe saw the world by sending something out of our eye and thatreflected from the object. In Platos time (427 347 B.C.), the reflection of light from smoothsurfaces was known. He was also a Greek. The ancient Greeks (about 200 A.D.) also first observed therefraction of light which occurs at the boundary of two transparentmedia of different refractive indices. 12 10. In the17th century, two scientists had differentviews about the nature of light Light is particlesNo! Lightis wavesIsaac Newton Christian Huygens1643 - 17271629 - 1695 14 11. I think light is a stream of tinyparticles, called Corpuscles 15 12. Corpuscular Theory of Light states that light consists oftiny particles that traveled instraight lines through space. 13. Newtons particle theory of light dominated optics during the18th century. Most scientists believed Newtons particle theory of lightbecause it had greater explanatory power.17 14. states that light is considered to consists electromagnetic waves that travel in a vacuum at the a speed of 3.0 x 10 m/s8 15. (source: Treatise on light, published by Huygens in1690)I think light is emitted as a series ofwaves in a medium he called aether(aether commonly also called ether)19 16. states that light is a form of wave disturbance which starts from a vibrating body is transmitted through space at great speed. 17. Wave theoryof light? No way!Albert Einstein1879 - 1955 21 18. states that light is a form ofenergy in discreet units calledquanta. The word quantummeans the smallest possible unitof energy. 19. states that light is composedof bundles of wave energyknown as photons 20. The photoelectric effect is observed when lightstrikes a metal, and emits electrons.Einstein used the idea of photons (light consists of tinyparticles) to explain results which demonstrate thephotoelectric effect. 24 21. Light is not particles,not waves, but BOTH!Louis de Broglie 251892 - 1987 22. states that light can be both a particleand a wave. If light interacting withlight, wave behavior tends to appeardominant and if light is interactingwith matter, particle or photonbehavior appears dominant.