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The Nature of Light

The Nature of Light. What is Light?. http://videos.howstuffworks.com/discovery/29406-assignment-discovery-electromagnetic-waves-and-light-video.htm A type of energy that travels as a wave Light does not require matter (medium) to travel

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The Nature of Light

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  1. The Nature of Light

  2. What is Light? • http://videos.howstuffworks.com/discovery/29406-assignment-discovery-electromagnetic-waves-and-light-video.htm • A type of energy that travels as a wave • Light does not require matter (medium) to travel • It is an Electromagnetic Wave (def) a wave that consists of changing electric and magnetic fields. • Vibrate at right angles to each other.

  3. Electric and Magnetic Fields • Electromagnetic Waves are changing electric and magnetic fields • An electric field surrounds every charged object. • Pulls oppositely charged objects towards it and repels like charged objects.

  4. Magnetic Fields • Surrounds every magnet • Iron filings form arcs.

  5. How are EM waves produced? • A electrically charged particle starts to vibrate. • When the particle vibrates, so does the electric field around it also vibrates. • When the electric field vibrates, a vibrating magnetic field is created. • This creates the Electromagnetic Wave that carries energy released by the original vibration of the particle. • Radiation(def) transfer of energy as electromagnetic waves.

  6. The Speed of Light • Scientist have not discovered anything that travels faster than the speed of light. • 300,000,000 m/s or 300,000 km/s • Light travels slower in air, glass and other types of matter. Why? • Why do you see lightening first then hear the thunder clap a few seconds later? • Light travels 880,000 times faster than sound! • If you could run at the speed of light, you could travel around the earth 7.5 times in 1s. • http://videos.howstuffworks.com/discovery/29407-assignment-discovery-speed-of-light-video.htm

  7. How fast is Light? Speed = Distance Time Time = Distance Speed The distance from earth to the moon is 384,000 km. Calculate the time it takes light to travel that distance. Time = 384,000 km = 1.28s 300,000 km/s

  8. Light from the Sun • It takes 8.3 min for light from the sun to reach us on earth. Earth is 350,000,000 km from the sun! • Only a small part of the total EM wave energy reaches the earth. • Most of the energy travels away in space.

  9. The Electromagnetic Spectrum • Electromagnetic Spectrum (def) all of the frequencies or wavelengths of electromagnetic radiation. • Visible and invisible light. • X rays, radio waves, microwaves. • All travel at the same speed in a vacuum • 300,000 km/s

  10. Radio Waves • A EM wave that has a long wavelength and low frequency. • Radio waves are broadcast. • Radio stations encode sound information into radio waves by varying either the wave’s amplitude or frequency. • This changing of amplitude or frequency is call modulation.

  11. Radio Waves • AM radio station- AM stands for amplitude modulation. • FM radio station – • FM stands for frequency modulation • AM radio waves are Longer than FM radio Waves. • AM waves travel further, but FM waves are less Affected by electrical Noise • http://videos.howstuffworks.com/science/radio-wave-videos-playlist.htm#video-29409

  12. Radio Waves and Television • Television waves are also carried by radio signals. • Short wavelengths and high frequency. • Some waves are transmitted to satellites and then carried over cables. Cable TV

  13. Microwaves • Short wavelength and high frequency. • Between 1mm and 30cm. • http://videos.howstuffworks.com/science/radio-wave-videos-playlist.htm#video-37744 • Cell phones use microwaves to send and receive communication

  14. Radar • Microwaves are used in radar. (Radio Detection and Ranging) • Police use a radar gun to send microwaves out that reflect off an object to record speed.

  15. Infrared Waves • Shorter wavelengths and higher speeds. • 700 nanometers and 1mm. • On a sunny day, your skin absorbs infrared waves and warms you up! • Almost all things give off infrared waves, buildings, trees, and you! • http://videos.howstuffworks.com/nasa/13514-ask-an-astronomer-infrared-explained-video.htm

  16. Visible Light • Very narrow range of wavelengths and frequencies, 400 nm and 700 nm. • White Light is light from the sun and is visible light of all wavelengths combined.

  17. Colors of Light

  18. Visible Spectrum • Roy G. BIV • Red, Orange, Green, Blue, Violet • The “I” stands for indigo (dark blue)

  19. Ultraviolet Light • Shorter wavelengths and higher frequencies than visible light. • 60 nm to 400 nm. • Bad Effects: • Too much can cause skin cancer, wrinkles and damage to your eyes. • Wear sun protection. SPF (sun protection factor) • Good Effects: • Ultra violet rays produce by ultraviolet lamps kill bacteria on food and surgical tools. • When exposed to light, skin cells produce vitamin D • Ricketts

  20. X Rays • Wavelengths between 0.001 nm and 60 nm • X Rays can pass through many materials. • One of the 100 greatest discoveries? • http://videos.howstuffworks.com/science-channel/29105-100-greatest-discoveries-discovery-of-x-rays-video.htm • How are X Rays used in everyday life?

  21. Gamma Rays • Wavelengths shorter than 0.1 nm • Can penetrate most materials very easily. • Used to kill cancer cells (tumors) • Side effect – may also kill some healthy cells • Used to kill bacteria in food.

  22. Interactions of Light Waves • Why do a cat’s/dog’s eyes glow in the dark when a light shines on them? • They have a special layer of cells in the back of their eyes that reflects light. • Reflection (def) the bouncing back of a ray of light, sound, or heat when the ray hits a surface that it does not go through • http://videos.howstuffworks.com/discovery/30016-assignment-discovery-reflection-and-refraction-video.htm

  23. The Law of Reflection • Light reflects off surfaces in the same way a ball bounces of surfaces. • If you bounce a ball straight up and down, it will bounce straight up. • If you bounce the ball at an angle, it will bounce away at an angle. • Law of Reflection states that the angle of incidence is equal to the angle of reflection

  24. Types of Reflection • Regular reflection- When light reflects of a very smooth surface, the light reflects all at the same angle. • Mirrors, water, shiny metals • Diffuse reflection- When light hits a surface that is not smooth, the light reflects at many different angles.

  25. Light Source or Reflection? • If you view a TV in a sunny room, you see the cabinet and the image on the screen. • If you view a TV in a totally dark room, you just see the image on the TV. • The light passes directly into your eyes. • Flames, light bulbs, and the sun. • Luminous(def)-Objects that produce visible light.

  26. Absorption • Absorption(def) the transfer of light energy to particles of matter. • As a beam of light shines through air, particles in the air absorb some of the energy from the light. • As a result the beam becomes dim

  27. Scattering of Light • Scattering(def) interaction of light with matter that causes the light to change its energy, direction of motion or both. • Because light scatters out of the light beam, the beam becomes dimmer.

  28. Refraction • Refraction(def) the bending of a wave as the wave passes between two substances in which the speed of the wave differs. • Speed of light varies depending on the material it passes through

  29. Refraction and Optical illusions • When you look at an object the light reflecting off the object travels in a straight line form the object to your eye. • Your brain interprets light as traveling in a straight line. • But when looking at an object underwater, the light reflected does not travel in a straight line. It refracts!

  30. Refraction and Color Separation • White light is composed of all the wavelengths of visible light. • When white light is passed through a prism, it is refracted twice. Violet has the shortest wavelength and Red has the shortest.

  31. Diffraction • Diffraction(def) a change in the direction of the wave when the wave finds an obstacle or an edge, such as an opening. • Greatest amount of diffraction occurs when the barrier or opening is the same size or smaller than the wavelength.

  32. Interference • Interference(def) the combination of two or more waves that results in a single wave. • Constructive interference- the wave has greater amplitude than the individual wave. • Destructive interference- the wave has smaller amplitude than the individual wave. Constructive interference, bright bands Destructive interference, the dark bands are formed, no light wave

  33. Light and Color • Light and Matter • When light strikes any form of matter, it can interact with the matter in three different ways: • Transmission(def) the passing of light or other form of energy through matter.

  34. Light and Color

  35. Why does the sun feel warm on my clothing?

  36. Types of Matter • Transparent(def) describes matter that allows light to pass through with little interference. • Translucent(def) describes matter that transmits light but does not transmit an image. • Opaque(def) describes an object that is not transparent or translucent

  37. Colors of Objects • How is an object’s color determined? • The color that an object appears to be is determined by the wavelengths of light that reach your eyes. • Light reaches your eye after being reflected off an object. • Your brain interprets the signals from your eyes as color

  38. When white light strikes an object, some colors of light are absorbed, and some are reflected.Only the light that is reflected reaches your eyes and is detected.

  39. What light is reflected off these objects?

  40. Colors of Transparent and Translucent Objects • Works differently than colors of opaque objects. • Determined by the color of light that is transmitted through the material. The other colors are absorbed. • Clear glass or plastic transmits all colors in white light. It appears clear. • Green bottles transmit green light. All other colors were absorbed.

  41. Mixing Colors of Light • What colors do I mix together to get white light? • Combine all the colors of light! • Or, just combine red, blue, and green (primary colors)

  42. Color Addition • Combining colors of light is called coloraddition. • When two primary colors of light are added together, you see a secondary color of light. • Cyan (blue + green), Magenta (blue + red), Yellow (red + green)

  43. Color TV • Uses color addition of the primary colors of light. • Groups of tiny red, green, and blue dots. • Each dot glows as it is hit by an electric beam. • http://videos.howstuffworks.com/science-channel/37745-deconstructed-plasma-tvs-video.htm

  44. Mixing Colors of Pigment • Have you ever been in Art class and tried to mix red, blue, and green to make white paint? • You can’t because paint contains pigment. • Pigment (def) substance that gives another substance or a mixture its color. • What pigments are found in nature? • Chlorophyll • Melanin (gives your skin its color)

  45. Color Subtraction • Primary pigments are Yellow, Cyan, and Magenta. • Mixing primary pigments together is called Color Subtraction.

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