The Electromagnetic Spectrum

1. The Electromagnetic Spectrum • Why are roses red and violets blue? • Why is the rainbow ROYGBIV? • What causes sunburn? • How fast is a speeding text? • X-rays? • What makes a remote control work? • What makes FM and AM different? • Is there really x ray vision? • What if we could see heat?

2. What is it? • The electromagnetic spectrum is the complete spectrum or continuum of light including radio waves, infrared, visible light, ultraviolet light, X-rays and gamma rays • An electromagnetic wave consists of electric and magnetic fields which vibrate, thus making waves.

5. Wavelength and Frequency • For any kind of wave there exists a simple relationship between wavelength and frequency. • The wavelength is measured as the distance between two successive crests in a wave. • The frequency is the number of wave crests that pass a given point in space each second. • Let’s Talk Frequency!

6. C = λν • The frequency (v) of a wave is the number of waves to cross a point in 1 second (units are Hertz – cycles/sec or sec-1) • λ is the wavelength- the distance from crest to crest on a wave

7. The product of wavelength and frequency always equals the speed of light. C = λν • Why does this make sense? • NOTE: c is a constant value= 3.00 x 108 m/s

8. Waves • Properties of waves include speed, frequency and wavelength • Speed (s), frequency (f) and wavelength (l) are related in the formula l x f = s • All light travels at a speed of 3 x 108 m/s in a vacuum

9. The speed of light! • The speed of light is the same for all seven forms of light. • It is 300,000 kilometers per second or 186,000 miles per second.

10. Wavelength, Frequency and Energy • Since all light travels at the same speed, wavelength and frequency have an indirect relationship. • Light with a short wavelength will have a high frequency • Light with a long wavelength will have a low frequency. • Light with short wavelengths has high energy • Light with long wavelengths has low energy

11. The Electromagnetic Spectrum • Radio Waves - communication • Microwaves – radar, weather prediction • Infrared- “heat waves” • Visible Light - detected by your eyes • Ultraviolet - causes sunburns • X-rays - penetrates tissue • Gamma Rays - most energetic

14. Radio waves • Low energy waves with long wavelengths • Includes FM, AM, radar and TV waves • Low frequency • Used in many devices such as remote control items, cell phones, wireless devices, etc.

15. MRI of the Brain

16. Radio(Low Frequency & Very High Frequency) • Emitted by • Astronomical Objects • Radio Station transmitters • Detected by • Ground based radio telescopes • Radios • By studying the radio waves originating from planets, comets, nebula astronomers can learn about their composition, structure, and motion.

17. Microwaves • Longer than radio, shorter than light and infrared • First used in radar, now used in communication, medicine and consumer use

18. Practical use for microwaves- besides mac and cheese! • Radar is an acronym for "radio detection and ranging". • Radar was developed to detect objects and determine their range (or position) by transmitting short bursts of microwaves. • The strength and origin of "echoes" received from objects that were hit by the microwaves is then recorded.

19. Invisible electromagnetic waves that are detected as heat Can be detected with special devices such as night goggles Used in heat lamps and remote controls Higher energy than microwaves but lower than visible light. In what situations might you see infrared as heat? How do we use infrared to view objects in space? Infrared waves

21. Infrared(Near and Thermal) • Emitted by • Sun and stars (Near) • TV Remote Controls • Food Warming Lights (Thermal) • Everything at room temp or above • Detected by • Infrared Cameras • TVs, VCRs, • Your skin

22. Night vision

23. Visible Light • The portion of the electromagnetic spectrum that human eyes can detect • ROY G BIV (red, orange, yellow, green, blue, indigo, violet) • Red is the lowest frequency and violet is the highest frequency • Why is the rainbow arranged this way? (think length of wavelengths.)

24. 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)

25. Herschel’s Experiment • Herschel’s Experiment • Discovered Invisible Light • In 1800, Herschel places his control thermometer just outside the red end of the spectrum • Result: The outside thermometer registered the highest temperature

27. Ultraviolet • Ultraviolet (UV) light has shorter wavelengths than visible light. • Though these waves are invisible to the human eye, some insects, like bumblebees, can see them • Emitted by • Tanning booths (A) • The sun (A) • Black light bulbs (B) • UV lamps • Detected by • Space based UV detectors • UV Cameras • Flying insects (flies)

28. X-Rays • High energy waves • When you get an X-ray taken at the hospital, X-ray sensitive film is put on one side of your body, and X-rays are shot through you. • Because your bones are dense and absorb more X-rays then your skin does, dark silhouettes of your bones are left on the X-ray film while your skin appears transparent • Used in medicine, industry and astronomy • Can cause cancer

30. Chandra X-ray Observatory • Chandra is designed to observe X-rays from high energy regions of the universe, such as the remnants of exploded stars. • The most sophisticated observatory built to date. • Deployed by the Space Shuttle Columbia on July 23, 1999, Chandra X-ray Observatory

31. Gamma rays • Photons with energies billions of times greater than visible light. • Blocked from Earth’s surface by the atmosphere. • Occur naturally from stellar objects like neutron (dead) stars • Gamma-ray bursts (from dead or dying stars) can release more energy in 10 seconds than the Sun will emit in its entire 10 billion-year lifetime! • Gamma rays are also man made for use in medicine

32. 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

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

35. Using the EM waves to view galaxies Animation—View a Galaxy at different wavelengths Viewing other astronomical objects- what makes each different?

36. Brief SUMMARY • A. All electromagnetic waves travel at the same speed. (300,000,000 meters/second in a vacuum. • B. They all have different wavelength and different frequencies. • Long wavelength-lowest frequency • Short wavelength highest frequency • The higher the frequency the higher the energy. • Checkpoint- interactive!

38. Time to think….. • 1. What is the relationship between frequency and wavelength? • 2. What is meant by ‘spectrum’? • 3. What does ROY G BIV mean?

39. Now, let’s really think • 4. Can you actually see x-rays? • Support your answer. • 5. Which color is more energetic, red or yellow? • 6. Which type of wave travels faster, gamma or radio? • 7. Why are microwaves more dangerous than radio waves?

40. Think about it…. • You have just been involved in a traffic incident that leaves you stranded on the side of the road. Which part of the electromagnetic spectrum would be of the most use to you and why?

41. Atoms and Light • The movement of electrons inside of atoms produces light and other electromagnetic radiation. • Sunlight produces every color in the rainbow but… • Each element gives off only certain frequencies of light, called spectral lines. In effect each element has its own signature of spectral lines allowing us to identify which element we have or what stars are made of.

42. Below is a picture of the spectral lines given off by hydrogen. Note there are 3 different frequencies.

43. The emission spectra makes it possible to identify inaccessible substances. Most of our knowledge of the universe comes from studying the emission spectra of stars. • Below is the spectra of a few more elements. Helium

44. Neon • Argon

45. In a star, there are many elements present. The way we can tell which are there is to look at the spectrum of the star. • From spectral lines astronomers can determine not only the element, but the temperature and density of that element in the star • Emission lines can also tell us about the magnetic field of the star. The width of the line can tell us how fast the material is moving

46. If the lines shift back and forth, it means that the star may be orbiting another star - the spectrum will give the information to estimate the mass and size of the star system and the companion star.

47. Around a compact object (black hole, neutron star), the material is heated to the point it gives off X-rays, and the material falls onto the black hole or neutron star. By looking at the spectrum of X-rays being emitted by that object and its surrounding disk, we can learn about these objects.

48. Examples from Space!

49. Think about it…. • You have just been involved in a traffic incident that leaves you stranded on the side of the road. Which part of the electromagnetic spectrum would be of the most use to you and why?

50. Answers • 1. Frequency and wavelength are properties of waves and since speed is constant for em waves, as frequency increases, wavelength decreases. • 2. Spectrum is a continuum of all electromagnetic waves • 3, ROY G BIV is the difference colors of the visible light in order of longest wavelength to shortest wavelength. • 4. X-rays can not be seen, only the waves in the visible light portion are visible. • 5. Yellow is higher energy than red because it has a shorter wavelength and higher frequency. • 6. Both travel at the same speed, 300,000 km/s (all em waves travel at the same speed) • 7. Microwaves have a higher frequency than radio and carry more energy.