3. Electromagnetic Waves

4. An Electromagnetic wave travels like a wave, but can interact with matter like a particle. It has a “dual nature”, behaving like a wave at times and behaving like particles (of NO mass!) at times. An Electromagnetic wave travels like a wave, but can interact with matter like a particle. It has a “dual nature”, behaving like a wave at times and behaving like particles (of NO mass!) at times.

5. When it is behaving like a particle, we call these massless bundles of energy photons.

6. Wave Behavior Electromagnetic waves reflect, refract, and diffract! diffract

7. Polarized waves If there are many waves and ALL the waves are vibrating in the same plane, they are said to be “polarized”

8. Polarized waves Electromagnetic waves are transverse waves and can be polarized. Longitudinal waves, like sound waves, cannot be polarized.

9. In a pure vacuum, all electromagnetic waves travel at the speed called “c”, which we call “the speed of light”, however the average speed slows down a little when it travels through substances such as water or glass as it interacts with the molecules. Albert Michelson is known for making an definitive measurement of the speed of light in the late 1800’s to early 1900’s, using a rotating mirror apparatus between 2 California mountains 22 miles apart. His value: 299,796 km/s. Accepted value today: 299,792 km/s He was the first American to win the Nobel Prize in physics. c = 3 x 10 8 m/s

10. As is true of ALL waves, Velocity = wavelength x frequency So, for electromagnetic waves, c = f

11. Now, you try one…. What is the frequency of purple light, which has a wavelength of 450 nm? 1 nanometer = 10 -9 m What is the frequency of purple light, which has a wavelength of 450 nm? 1 nanometer = 10 -9 m

12. Don’t just sit there! Get out a calculator and find the frequency. c = f c = 3 x 10 8 m/s  450 nm (1 nm = nanometer = 10 -9 m) What is f, the frequency? f = c ÷ f = 3 x 10 8 ÷ (450 x 10 -9 ) f = 6.67 x 10 14 Hz

13. How to make an electromagnetic wave: Something must be vibrating to produce a wave. What IS vibrating to produce an electromagnetic wave? A vibrating ( accelerating! ) electric charge creates a wavy electric field that produces a wavy magnetic field that produces an electric field that produces a magnetic field……… electric charge …

14. Electromagnetic waves Electromagnetic waves are transverse waves of intertwined electrical and magnetic fields.fields

15. “Visible Light” is only a VERY small part of the ELECTROMAGNETIC SPECTRUM. It is the only part of the EM spectrum that is VISIBLE to us. The entire spectrum, in order from long wavelength to small wavelength, is

16. Rattlesnakes May Inject Venom Under Xtreme Grumpiness

17. “ Light ”

18. Our color spectrum is only a very small part of the electromagnetic spectrum.

19. “Visible Light” is the part of the electromagnetic spectrum that is in RESONANCE with the rods and cones in our retinas.

20. All electromagnetic waves are the same kind of wave. Blue light is the same type of wave as X-rays. Their names (microwave, infrared, radio, etc.) are based only on a particular range of wavelengths (or frequency). All electromagnetic waves travel at the “speed of light” in a vacuum.

21. Radio waves : used by all TV and Radio stations and garage door openers, have very long wavelengths so that they are not easily blocked by objects like buildings. Frequencies: AM radio stations broadcast in kHz. FM stations broadcast in MHz. TV stations broadcast in Mhz. What is the wavelength of our public radio station, FM 90.1? (90.1 x 10 6 Hz) Using c = f, = ? = 3.3 m

22. Microwaves have an energy that is easily absorbed by water molecules. This is why they are used in “microwave ovens”. What happens is that when the water in your TV dinner absorbs the microwaves, it makes the water molecules vibrate faster. The energy of the microwaves is converted into heat. Cell phone calls, radar and “bluetooth” are all transmitted using microwaves. Some people are frightened that the waves coming in and out of their cell phones are short enough (energetic enough) to cook their brains. (They aren’t!)

23. Infrared : These waves have a shorter wavelength than microwaves, but is still longer than visible light. IR waves are used in remote controls for your TV Animals like the pit-viper have infra-red detectors so that they can find their prey in the dark. You have been warned !! Infrared radiation is associated with HEAT. Every object that emits heat is emitting IR. Our bodies can “feel” IR if the source is close enough and hot enough.

24. The Visible Spectrum The Visible Spectrum Roy G Biv : Red, Orange, Yellow, Green, Blue, Indigo, and Violet are the colors of visible light. Wavelength range from about 700 - 400 nm 1 Nanometer = 10 -9 m

25. Ultraviolet : These waves have very high energy and very short wave lengths- shorter than visible light. Too much exposure to UV can cause skin cancer- too little exposure and we don’t produce enough Vitamin D! UV is sometimes used to sterilize tools, glassware, and kill bacteria on food. Some animals like honey bees can see ultraviolet waves.

26. Even shorter wavelength: X-Rays have so much energy and such a short wavelength that they can go right through you. They also mess with your DNA… that’s bad However, they cannot get through bone as easily as they can get through muscle. This is because your bones contain so much Calcium.

27. The very shortest, highest frequency: Gamma rays These are nasty ones. They have very high energy and will even go through metals if they are not thick layers. Some radioactive materials produce gamma rays (on Earth) as do super nova explosions and pulsars (out in space). Gamma rays and X-Rays can cause cancer, but gamma rays can also be used to destroy cancer cells: this is radiation therapy.

29. Light and Colors

30. Light vs Pigments If light passes through a substance, the substance is said to be

31. Light vs Pigments If light passes through a substance, the substance is said to be transparent.

32. Light vs Pigments If light passes through a substance, the substance is said to be transparent. If light partially passes through a substance, it is said to be

33. Light vs Pigments If light passes through a substance, the substance is said to be transparent If light partially passes through a substance, it is said to be translucent.

34. Light vs Pigments If light passes through a substance, the substance is said to be transparent. If light partially passes through a substance, it is said to be translucent. If light will not pass through a substance, it is said to be

35. Light vs Pigments If light passes through a substance, the substance is said to be transparent. If light partially passes through a substance, it is said to be translucent. If light will not pass through a substance, it is said to be opaque.

36. An object that produces light is

37. LUMINOUS

38. An object that produces light is LUMINOUS An object that reflects light is

39. An object that produces light is LUMINOUS An object that reflects light is ILLUMINATED

40. Isaac Newton was the first to show that white light consists of every color light mixed together. He sent white light through a prism, which produced a rainbow of colors and then through a second prism, where it recombined to produce white light again. All the colors, on atop the other, combine to produce white light.

42. The Primary colors of VISIBLE LIGHT The three primary colors of light are red, green, and blue.primary colors Adding two primary colors of light produces the secondary colors of light. Green plus blue produces cyan. Blue plus red produces magenta. Red plus green produces yellow. Red plus green plus blue produces white.

43. Two colors of light are complementary if they produce white when added together. The complementary pairs are: Green and magenta Red and cyan Blue and yellow

44. Pigments are chemicals that are used to produce different colors of paint or dyes. The primary pigments absorb ONE primary color and reflect the other two primary colors back to our eyes. The primary pigments are the same as the secondary colors.primary pigments Cyan pigment absorbs red and reflects back blue and green.Cyan pigment absorbs red and reflects back blue and green. Magenta pigment absorbs green and reflects blue and red.Magenta pigment absorbs green and reflects blue and red. Yellow pigment absorbs blue and reflects red and green.Yellow pigment absorbs blue and reflects red and green.

45. Why does red brick look red?? What color will a green apple appear to be when viewed in red light or green light or blue light or ….??? We SEE the color of objects when light from some light source reflects off them. We only see the colors that reflected. All other frequencies from the light source that are not seen must have been absorbed by the object.

47. The sky is blue because the atmospheric molecules are in resonance with blue light. The sky is blue because the atmospheric molecules are in resonance with blue light. When white light comes from the sun, the blue waves are absorbed and reemitted in all directions by the air molecules. So the sky will look blue and the sun will have “lost” a little of its blue waves so that it will look slightly yellow (red and green). This is called “Rayleigh scattering”.

48. The sunrises and sunsets look yellow and orange and red because the white light from the sun has to pass through so much more of the atmosphere to reach our eyes as we look towards the sun at the horizon. Because of that, virtually all of the blue light will have been scattered by the air molecules, leaving only red and green for us to see.

49. The oceans look blue-green because the ocean waters (with algae and other microorganisms and impurities) absorb red light and only reflect back to our eyes the blue and green of the spectrum.

50. Green Flash

52. Polarization If the vibrations of a wave are back and forth in one plane, the wave is said to be polarized.polarized A single vibrating electron produces a single polarized wave. But a light source usually has millions of electrons vibrating in all directions so that the waves are not polarized. Only transverse waves can be polarized. Longitudinal waves, like sound, cannot be polarized.

53. Polarization A polarizer is a type of material that allows only waves vibrating in one plane (its polarizing axis) to pass through, so that it produces polarized light waves.

54. Polarization What if light goes through two polarizing filters? If their polarizing axis are aligned, light will pass through both filters. However, if the polarizing axis are perpendicular, no light will pass through.

55. Materials that rotate the orientation of light (the plane in which it is vibrating) as it passes through are said to be optically active. If an optically active substance is placed between 2 crossed polarizing filters, some light will pass completely through since the polarized waves from the first filter will have been rotated before they strike the second filter.