# "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

## About "The Wave Model and History of Light"

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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.

Slide2Lasers

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.

Slide12Rainbow

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

Slide23Wave... 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

Slide32MagneticResonance Imaging

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

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

Slide41X-RayImaging

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