Light intro
- 2. 2) Properties of light 3) Theories about light
- 4. • Light travels in straight lines: Las e r
- 5. • Light travels VERY FAST – around 300,000 kilometres per second. At this speed it can go around the world 8 times in one second.
- 6. • 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.
- 7. • We see things because they reflect light into our eyes: Homework
- 8. • 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
- 9. • Shadows Shadows are places where light is “blocked”: Rays of light
- 10. • 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
- 12. • Aristotle (384 - 322 B.C.), an ancient Greek thinker, thought that we saw the world by sending “something” out of our eye and that reflected from the object. • In Plato’s time (427 – 347 B.C.), the reflection of light from smooth surfaces was known. He was also a Greek. • The ancient Greeks (about 200 A.D.) also first observed the refraction of light which occurs at the boundary of two transparent media of different refractive indices. 12
- 14. In the17th century, two scientists had different views about the nature of light …… Light is particles No! Light is waves Isaac Newton Christian Huygens 1643 - 1727 1629 - 1695 14
- 15. I think light is a stream of tiny particles, called Corpuscles … 15
- 16. • Corpuscular Theory of Light states that light consists of tiny particles that traveled in straight lines through space.
- 17. • Newton’s particle theory of light dominated optics during the 18th century. • Most scientists believed Newton’s particle theory of light because it had greater explanatory power. 17
- 18. 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
- 19. (source: Treatise on light, published by Huygens in 1690) I think light is emitted as a series of waves in a medium he called “aether” (“aether” commonly also called “ether”) 19
- 20. states that light is a form of wave disturbance which starts from a vibrating body is transmitted through space at great speed.
- 21. Wave theory of light? “No way!” Albert Einstein 1879 - 1955 21
- 22. states that light is a form of energy in discreet units called quanta. The word quantum means the smallest possible unit of energy.
- 23. states that light is composed of bundles of wave energy known as photons
- 24. The photoelectric effect is observed when light strikes a metal, and emits electrons. Einstein used the idea of photons (light consists of tiny particles) to explain results which demonstrate the photoelectric effect. 24
- 25. Light is not particles, not waves, but BOTH! Louis de Broglie 25 1892 - 1987
- 26. states that light can be both a particle and a wave. If light interacting with light, wave behavior tends to appear dominant and if light is interacting with matter, particle or photon behavior appears dominant.