• Light travels VERY FAST – around 300,000 kilometres per second.At this speed it cango around the world 8times in one second.
• 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.
• We see things because they reflect light into our eyes: Homework
• 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
• ShadowsShadows are places where light is “blocked”: Rays of light
• 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
• 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
In the17th century, two scientists had differentviews about the nature of light …… Light is particles No! Light is wavesIsaac Newton Christian Huygens1643 - 1727 1629 - 1695 14
I think light is a stream of tinyparticles, called Corpuscles … 15
• Corpuscular Theory of Light states that light consists of tiny particles that traveled in straight lines through space.
• 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
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
(source: Treatise on light, published by Huygens in1690) I think light is emitted as a series of waves in a medium he called “aether” (“aether” commonly also called “ether”) 19
states that light is a form of wave disturbance which starts from a vibrating body is transmitted through space at great speed.
Wave theoryof light? “No way!” Albert Einstein 1879 - 1955 21
states that light is a form of energy in discreet units called quanta. The word quantum means the smallest possible unit of energy.
states that light is composed of bundles of wave energy known as photons
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
Light is not particles,not waves, but BOTH! Louis de Broglie 25 1892 - 1987
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.