"The Wave Model and History of Light"
In Grade 8 Science Unit 2 on Optics, students will study the wave model of light and how various properties of light can be understood through this model. Chapter 4 of
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Slide1Grade 8 Science Unit 2: Optics Grade 8 Science Unit 2: Optics Chapter 4 : Many properties of light can be understood using a wave model of light.
Slide3The History of Light The History of Light Pythagoras A Greek philosopher Believed that beams of light were made of tiny particles. The eyes detected these particles and could see the object.
Slide4Albert Michelson First person to measure the speed of light (3 x 10 m/s) 8
Slide5Speed: Light vs. Sound Speed: Light vs. Sound Light 1 000 000 000 km/h Sound 1 200 km/h
Slide6Thunder & Lightning
Slide7Both the lightning strike and the roar of thunder happen at the same time. You see the lightning first. If you multiply the time in seconds between the strike and the roar by the speed of sound, you will find the approximate distance.
Slide8Orion's BeltThe light takes thousands of years to reach our eyes
Slide9Light Technologies Include... Light Technologies Include... Microscope Telescope Periscope Binoculars Fibre optics Camera
Slide10Prescription contact lenses Laser Movie projectors Overhead projectors
Slide11LightLight Light: a form of energy that can be detected by the human eye. Visible light: a mixture of all the colors of the rainbow.
Slide13Properties of Visible Light... Properties of Visible Light... 1. Light travels in a straight line. ( rectilinear propagation )
Slide142. Light reflects (reflection ) Mirror Dust
Slide153. Light refracts (Refraction ) “The Bent Stick Effect”
Slide164. Light Disperses( dispersion ) Light separates into its constituent colors.
Slide175. Light travels through avacuum (does not require a medium; no particles involved)
Slide186. Travels through objects todifferent degrees
Slide19Visible Light Spectrum Visible Light Spectrum Can be seen due to the dispersion of light through a prism.
Slide20The constituent colors ofwhite light are: Red Orange Yellow Green Blue Indigo Violet ROY G BIV **Red has the smallest refraction and violet has the greatest.
Slide21When a laseris shone through a prism, the light will refract but disperse. Why? A laser light is one color only!
Slide22The Wave Model The Wave Model Explains that light is a type of wave that travels through empty space and transfers energy from one place to another
Slide23A Wave... A Wave... * A Peak is also called the crest .
Slide24Frequency: the number of repetitive motions that occur during a given time. Ex. The number of wavelengths that pass a point in 1 second. Measured in Hertz
Slide25Amplitude: the height of a wave crest or depth of a wave trough as measured from the rest position. crest height = trough depth The larger the amplitude, the greater the energy transported.
Slide26Wavelength: the distance from crest to crest, trough to trough or the distance covered by one complete crest and one complete trough. Measured in meters Longer wavelengths refract the least.
Slide27Frequency and Wavelength Frequency and Wavelength High frequency waves have short wavelengths Low frequency waves have short wavelengths
Slide29Electromagnetic Radiation Electromagnetic Radiation The transmission of energy in the form of waves that extend from the longest radio waves to the shortest gamma rays.
Slide31Types of Electromagnetic Radiation Types of Electromagnetic Radiation 1. Radio waves : the longest wavelength and lowest energy and frequency. Can be used to help us see the inside of our bodies to diagnose illness. Ex. MRI
Slide332. Microwaves : have the shortest wavelength and the highest frequency of all radio waves. Ex. Microwave ovens, telecommunication satellites, radio telescopes, radar (remote sensing)
Slide34How a Microwave WorksMicrowave ovens use a specific frequency that is strongly absorbed by water molecules in food.
Slide353. Infrared Waves : longer wavelength and lower energy and frequency. Infrared means below red Also called heat radiation Ex. Remote controls, computer, heat lamps, motion sensors
Slide36Infrared RadiationLANDSAT Image of Fire
Slide374. Visible Light Spectrum Can be continually detected by our eyes.
Slide385. Ultraviolet Waves : shorter wavelength and higher energy and frequency. Very energetic Have the ability to kill bacteria in food and water and medical supplies. Ex. Sun, detect fingerprints
Slide406. X-Rays : have a shorter wavelength, and higher energy and frequency than UV. Used to photograph teeth, bones and the inside of machines, security screening
Slide427. Gamma Rays : have the highest energy and frequency and the shortest wavelength. Result from nuclear reactions. Produced by the hottest regions of the universe.
Slide43GammaRays: Nuclear Explosion Gamma Rays: Medical Treatment
Slide44Electromagnetic Radiation... A Safety Concern? Electromagnetic Radiation... A Safety Concern? Generally, higher energy electromagnetic radiation is more harmful to humans. The Earth’s atmosphere is able to protect us from some of the more dangerous electromagnetic radiation present in space, making the Earth a safe place for humans. Changes to present conditions may comprise our safety.
Slide45Positive and Negative Effects to Exposure to Electromagnetic Radiation Positive and Negative Effects to Exposure to Electromagnetic Radiation X-Rays Ultraviolet Radio Waves Positive Effects Medical detection Used to treat jaundice in babies Improved tele- communication Negative Effects Over- exposure can lead to cancer Skin cancer Uncertain of long-term exposure