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Light and the Electromagnetic Spectrum

Light and the Electromagnetic Spectrum. Light. Our primary source of light is the sun . Light travels in straight lines at a speed of 186,000miles per second . *Light waves travel faster than sound waves!

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Light and the Electromagnetic Spectrum

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  1. Light and the Electromagnetic Spectrum

  2. Light • Our primary source of light is the sun. • Light travels in straight lines at a speed of 186,000miles per second. • *Light waves travel fasterthan sound waves! • Light energy from the sun travels through space , reaches earth, and some of it turns to heat energy and warms the earth’s air. • Light from the sun also travels to the cells of green plants (producers) and is stored as energy. • When light reaches an object, it is absorbed, reflected, or passes through it.

  3. Sensing Light • Humans have two light detectors. • Do you know what they are called?

  4. How many sources of Light can you list and explain? • SUN=warms air, water, and land. • Fire=provides heat, light, and cooking fuel. • Lightning= • Firefly= • Flashlight= • Light bulb= • Laser beams= • Optical telephone fibers= *Trafficlights= *AIMS: Primarily Physics: Light Sources Activity

  5. Think Pair Write(Talk with a partner and write your answer in your notebook) • 1. A person will see a flash of lightning before they hear the thunder that goes with it because? • 2.Can you draw a long wavelength and a short wavelength next to it? • 3.What scientific tools are used to study light? • 4. Can you contrast objects that are transparent, translucent, and opaque?

  6. “Just Passing Through:” What happens when light strikes glass? Or waxed paper? Or a book? • If light travels through an object it is =transparent • If light is blocked by an object and a dark shadow is cast it is= opaque. • If some light passes through but not all and a light shadow is present it is=translucent. *AIMS:Primarily Physics: Just Passing Through Activity

  7. What happens when light hits these objects? • Glass of water • School bus window • Notebook paper • Waxed paper • Plastic wrap • Tissue paper • Cardboard • Textbook • Hand lens…

  8. Transparent objects: • The windows on a school bus, • A clear empty glass, • A clear window pane, • The lenses of some eyeglasses, • Clear plastic wrap, • The glass on a clock, • A hand lens, • Colored glass… • ALL of these are transparent. Yes, we can see through them because light passes through each of them.

  9. Translucent objects • Thin tissue paper, • Waxed paper, • Tinted car windows, • Frosted glass, • Clouds, • All of these materials are translucent and allow some light to pass but the light cannot be clearly seen through.

  10. Opaque objects: • Heavy weight paper, • Cardboard • Aluminum foil, • Mirror, bricks, buildings, • Your eyelids and hands, • Solid wood door, • All of these objects are opaque because light cannot pass through them at all. • They cast a dark shadow.

  11. Light Phenomenon Isaac Newton (1642-1727) believed light consisted of particles By 1900 most scientists believed that light behaved as a wave.

  12. Light is Particles and Waves Albert Einstein returned to the idea that light existed as particles. He proposed that light could be described as quanta of energy that behave as if they were particles. Light quanta are called photons.

  13. Waves (C = λν) The frequency (v) of a wave is the number of waves to cross a point in 1 second λ is the wavelength- the distance from crest to crest on a wave

  14. Triangular Prism

  15. The Electromagnetic Spectrum The electromagnetic spectrum represents the range of energy from low energy, low frequency radio waves with long wavelengths up to high energy, high frequency gamma waves with small wavelengths.

  16. Visible Light Visible light is a small portion of this spectrum. This is the only part of this energy range that our eyes can detect. What we see is a rainbow of colors. RedOrangeYellowGreenBlueIndigoViolet ROY G BIV

  17. Our Eyes The human eye is most sensitive to yellow- green It is no coincidence that this wavelength falls within the range of wavelengths at which the Sun emits most of its electromagnetic energy—our eyes have evolved to take greatest advantage of the available light.

  18. Colors The colors we see in objects are the colors that are reflected, all other colors are absorbed. A red t-shirt appears red because red is reflected to our eyes and the other colors are absorbed. When all colors are being reflected we see white light (white isn’t really a color)

  19. Colors When all wavelengths of light are being absorbed we see black (black also, isn’t really a color)

  20. Why the Sky is Blue Ultraviolet light from the sun is absorbed by the protective layer of the ozone gas. Visible frequencies of violet light is scattered. Although the violet light is scattered more, our eyes are only sensitive to blue. That’s why we see a blue sky.

  21. Blue Sky

  22. Why Water is Greenish Blue Water is transparent to almost all the visible frequencies of light. The color is actually the reflected color of the sky Red is absorbed by the molecules in the water

  23. Don’t’ forget…longest waves (radio) ..to shortest waves (Gamma)

  24. Radio Waves Have the ______ wavelengths, the ______ frequencies, and the ______ energies Examples of radio waves are AM/FM radio and broadcast television

  25. Microwaves EM waves with ______ wavelengths, higher frequencies, and _____ energy than other radio waves Radar – radio detection and ranging. Used to control air traffic at airports, analyze ________ conditions and measure the speed of a moving vehicle Radar led to the invention of ________ ovens Cell phones – radio transmitter and receiver that uses ________

  26. Infrared Light Type of EM wave most often associated with ______ Sometimes referred to as _____ rays You can feel it as warmth coming from the sun, a fire, or a radiator Infrared lamps are used to provide ______ in bathrooms and to keep food warm after its been cooked Some animals can see in _____ light

  27. Visible Light The part of the EM spectrum that _____ eyes can see. Longest wavelengths are _____ all the way to violet ROY G BIV Red, Orange, Yellow, Green, Blue, Indigo, Violet

  28. Ultra-Violet Light Has more energy than _____ light The waves in this range can ______ your skin and eyes Sun block and UV-protection sunglasses are designed to filter out the _______ frequencies UV light can be used to sterilize medical instruments and food by _____ harmful bacteria UV light causes skin cells to _______ vitamin D which is essential to good health UV light is ______ to some animals. Bees and some other insects

  29. X-rays Has a very ______ frequency and ______ Pass easily through soft tissues of the body, but are absorbed by the _____ The _______ pass through exposing the film where there is no bone When getting x-rays other parts of the body are covered with a _____ vest to block the x-rays

  30. Gamma-Rays ________ frequencies and energies of any ___ waves Produced by some radioactive substances as well as the ____ and other _____ Gamma rays can penetrate the soft and the hard tissues of the body, killing normal cells and causing cancer cells to develop Gamma rays can also be used to kill _____ cells and _____ tumors

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