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Unit 4: Optics. Our eyes work like a camera, recording exactly what they are pointed at. Agree/ Disagree??. Perception is NOT reality. WHAT IS LIGHT ???. SOLAR CELLS. SOLAR COOKER. SOLAR WATER HEATER. Two Properties of Light. #1 - Light is a form of energy. It’s the only form we can see
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Our eyes work like a camera, recording exactly what they are pointed at. Agree/ Disagree??
Two Properties of Light • #1 - Light is a form of energy. • It’s the only form we can see • #2 Light Travels in Straight Lines
DISPERSION of Light http://www.youtube.com/watch?v=7Fl0GZsBhGo http://www.youtube.com/watch?v=9eEyTw4wylk
DISPERSION OF LIGHT • Electromagnetic waves can move through empty space but can be absorbed by matter. • These waves also carry other forms of energy such as radio and TV signals, microwaves, ultraviolet waves, X-rays and many others. http://www.chronicle.su/wp-content/uploads/prism.jpg
Electromagnetic waves can move through empty space but can be absorbed by matter. • These waves also carry other forms of energy such as radio and TV signals, microwaves, ultraviolet waves, X-rays and many others.
Electromagnetic Waves • Electromagnetic waves can move through empty space but can be absorbed by matter. • These waves also carry other forms of energy such as radio and TV signals, microwaves, ultraviolet waves, X-rays and many others.
Each type of electromagnetic wave has a distinct wavelength (the distance from one peak to the next). • It is the wavelength that determines the type of electromagnetic wave or the colour of visible light.
How do we see light sources? • Light travels from a source to our eyes. • We can see sources in a dark room. Method #1
How do we see things that are not sources of light? Light bounces off and some reaches our eyes. Method #2 • If there is no light we cannot see anything!
When we view an object, light travels in a straight line from the object to our eye. Scientists use an arrow called a ray to represent the path light is travelling. A Ray
TWO BASIC PROPERTIES OF LIGHT • Property No. 2 • Light travels in a straight line If you stand in front of a movie screen, part of the view will be blocked. This is because light will not bend around you to reach the screen.
Transmission • When light strikes an object, three things can happen: • Transmission: This is the process in which light passed through an object and keeps travelling (e.g. a clear window, tracing paper). Objects that transmit light are called transparent or translucent.
Reflection: This is the process of light “bouncing off” an object (e.g. a mirror, a piece of white paper).
#3 - Absorbtion • #3 Absorption: This is the process in which light is retained by an object and converted to heat. • A black shirt gets very hot in the sun because it absorbs all forms of visible light and does not reflect any back. • The characters on this page are recognized by your eye since they do not reflect light back. This lack of light is recognized by the brain as the “colour” black. • Objects that reflect or absorb light are called opaque.
Property Two Light Travels in a Straight Line • Until light strikes something, it will continue to travel in a straight line. • If light strikes a clear substance, like water or a window, it will pass through them. These media are transparent. • Other media let light through diffusely. These media are called translucent. Wax paper is translucent. • Finally some materials will not allow any light to pass through. These materials are called opaque. Examples include books
Practice • Label the following objects as transparent, translucent or opaque • Baseball, 2. Window, 3. Mirror, 4. Aquarium Label the following as examples of transmission, reflection or absorbtion. • Looking through Binoculars • Hiding behind a tree • Look at the surface of a lake
Practice • Label the following objects as transparent, translucent or opaque • Baseball, 2. Window, 3. Mirror, 4. Aquarium Opaque Transparent Opaque Translucent Label the following as examples of transmission, reflection or absorbtion. • Looking through Binoculars (transmission) • Hiding behind a tree (Absorbtion) • Look at the surface of a lake (Transmission/Reflection)
