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ELECTROMAGNETIC SPECTRUM

ELECTROMAGNETIC SPECTRUM. Electromagnetic Radiation. Definition: Radiant energy emitted by all matter whose temperature is greater than absolute zero (0° K). Best known as VISIBLE LIGHT but includes radio waves and ultraviolet waves too. Light and the EM Spectrum.

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ELECTROMAGNETIC SPECTRUM

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  1. ELECTROMAGNETIC SPECTRUM

  2. Electromagnetic Radiation • Definition: Radiant energy emitted by all matter whose temperature is greater than absolute zero (0° K). • Best known as VISIBLE LIGHT but includes radio waves and ultraviolet waves too.

  3. Light and the EM Spectrum • The terms light, radiation, and electromagnetic wave can all be used to explain the same concept. • Light comes in many forms. • x-rays, visible light, radio waves, etc. are all the same phenomena • By using these different wavelengths, astronomers are able to gain a lot of information on various objects Jupiter seen at different wavelengths of light tells you different things.

  4. Light and EM Radiation • Electromagnetic Radiation can travel through empty space (without a medium). • They travel as vibrations in electrical and magnetic fields • All forms of EM radiation travel at the SAME SPEED. • Speed of Light = 300,000 Km/sec • Speed of Sound = 340 m/sec (.340 km/sec) Click here Animation: Interaction of vibrating charges

  5. Light as Waves • One way to think about light is as a traveling wave • A wave is just a disturbance in some medium (water, air, space) • A wave travels through a medium but does not transport material • A wave can carry both energy and information

  6. Wave Terminology • Wavelength - distance between two like points on the wave • Amplitude - the height of the wave compared to undisturbed state • Period - the amount of time required for one wavelength to pass • Frequency - the number of waves passing in a given amount of time

  7. Electromagnetic Spectrum • Electromagnetic Spectrum—name for the range of electromagnetic waves when placed in order of increasing frequency • Click here (Animation—Size of EMwaves)

  8. The Electromagnetic Spectrum • Human eyes see the visible part of the spectrum • Longer wavelengths includesinfrared light, microwaves, and radio • Shorter wavelengthsincludesultraviolet light, X-rays, and gamma rays • All of these are forms of electromagnetic radiation

  9. RADIO WAVES • A. Have the longest wavelengths and lowest frequencies of all the electromagnetic waves. • B. A radio picks up radio waves through an antenna and converts it to sound waves. • C. Each radio station in an area broadcasts at a different frequency. # on radio dial tells frequency.

  10. MRI of the Brain • MRI (MAGNETIC RESONACE IMAGING) • Uses Short wave radio waves with a magnet to create an image

  11. Radio Waves • FM=Frequency modulation—waves travel in a straight line & through the ionosphere--lose reception when you travel out of range. • AM=Amplitude modulation—waves bounce off ionosphere can pick up stations from different cities.

  12. MICROWAVES • Microwaves—have the shortest wavelengths and the highest frequency of the radio waves. • Used in microwave ovens. • Waves transfer energy to the water in the food causing them to vibrate which in turn transfers energy in the form of heat to the food. • Used by cell phones and pagers. • RADAR (Radio Detection and Ranging) • Used to find the speed of an object by sending out radio waves and measuring the time it takes them to return.

  13. INFRARED RAYS • Infrared= LONGER than the color red • Shorter wavelength and higher frequency than microwaves. • You can feel the longest ones as warmth on your skin • Heat lamps give off infrared waves. • Warm objects give off more heat energy than cool objects.

  14. INFRARED RAYS Thermogram—a picture that shows regions of different temperatures in the body.

  15. Wavelengths of Light - Visible • What we see as white light is actually made up of a continuum of components • We break white light into red, orange, yellow, green, blue, indigo, and violet (ROY G BIV) • Red is the LONGEST • Violet is the SHORTEST • Visible light is the Smallest section of the EM Spectrum

  16. ULTRAVIOLET RADIATION • Referred to as UV rays • Shorter wavelength and higher frequency than visible light • Carry more energy than visible light • Used to kill bacteria. (Sterilization of equipment) • Causes your skin to produce vitamin D (good for teeth and bones) • Used to treat jaundice ( in some new born babies. • Too much can cause skin cancer. • Use sun block to protect against (UV rays)

  17. XRAY RADIATION • Shorter wavelength and higher frequency than UV-rays • Carry a great amount of energy • Can penetrate most matter. • Bones and teethabsorb x-rays. (The light part of an x-ray image indicates a place where the x-ray was absorbed) • Too much exposure can cause cancer • (lead vest at dentist protects organs from unnecessary exposure)

  18. GAMMA RADIATION • Shorter wavelength and higher frequency than X-rays • Carry the greatest amount of energy and penetrate the most. • Used in radiation treatment to kill cancer cells. • Can be very harmful if not used correctly.

  19. EM Spectrum in Astronomy • If we could only observe in visible light, our knowledge of the universe would be greatly limited • By looking at objects at different wavelengths, we get a different view and lots more information • Some objects are only visible at certain wavelengths

  20. The Sun at Different Wavelengths Visible Ultraviolet X-ray X-ray

  21. TELESCOPES • Invented by Dutch lens maker in 1608 • Galileo: designed small 30X scope • Observed the moon and “began” the modern age of Astronomy where measurement was more important than philosophy

  22. General types of Telescopes • Refracting (objective is a glass lens) • Reflecting (objective is a mirror) • Newtonian • Cassegrain

  23. Problems with Earth-based telescopes • Earth’s atmosphere reflects certain wavelengths • x-rays, gamma rays and most UV light is not transmitted by our atmosphere • Earth’s atmosphere blurs images • the bending of light by the atmosphere depends on the temperature of the “air” • “twinkling of stars” (Caused by movement of air) • “Light pollution” • Solution? Put the telescope in space.

  24. Advantages of Space Telescopes • Can collect EM wavelengths that do not penetrate the Earth’s atmosphere • Gamma rays • X-rays • Most Ultraviolet waves • Can collect all EM radiation without disruption from Earth’s atmosphere • Images MUCH sharper

  25. Disadvantages of space-based telescopes • Expensive to launch and maintain • Difficult to repair • Short lifetime

  26. HUBBLE SPACE TELESCOPE • Launched in 1990 • Mirror error fixed ‘93 • 15 yr life expectancy • Going on year 20!! • 96 minutes for 1 orbit around Earth

  27. HUBBLE IMAGES

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