1. The Electromagnetic Spectrum and Light (Sections 18.1-18.3 only)
Chapter 18
The Electromagnetic Spectrum and Light
(Sections only)

2. 18.1 Electromagnetic Waves

3. What Are Electromagnetic Waves?
EM waves consist of changing electric fields and magnetic fields. EM waves carry energy from place to place.

4. How are EM waves produced?
When an electric field changes, so does the magnetic field. The changing magnetic field causes the electric field to change. When one field vibrates—so does the other. EM waves are produced when an electric charge vibrates or accelerates. In other words it is produced in constantly changing fields.

5. How are EM waves produced?
Electromagnetic waves are produced when an electric charge vibrates or accelerates.
See animation here
Back up link #3

6. How they travel
EM waves can travel through a vacuum, or empty space, as well as through matter. This is called electromagnetic radiation.

7. Did you know? The speed of light is constant in a vacuum.
Speed of light (c) = 3.00 x 108 m/s

8. Wavelength and Frequency
EM waves vary in wavelength and frequency despite traveling at the same speed. Speed of light (c) = wavelength x frequency

9. Quick Facts Speed: 3.0 x 108 m/sec (speed of light) Wavelength: varies
Frequency: varies
Travels in a straight line (need satellites to account for this problem)
Video Clip (3:28)

10. 18.2 Electromagnetic Spectrum

11. Electromagnetic Spectrum
Radio waves
Infrared rays
Visible light
Ultraviolet rays
X-rays
Gamma rays

12. Radio Waves AM (frequency is the same and amplitude changes)
FM (frequency changes and amplitude is the same)

13. Which is AM radio?

14. Television Waves
Same as radio but also sends pictures.

15. Microwaves
Waves of this frequency are absorbed by water and heat food.
Food is in motion and therefore creates heat

16. How is a cell phone like a microwave?

17. Get off the phone!
10950 watts is the same as 1.09 kWatts

18. Now tell me how a cell phone is like a microwave!!
If you talk on cellular phone more than 20 min. your brain temperature raises for up to 2 degrees.

19. Low wavelength, frequency & energy

20. Infrared Rays Used as a source of heat
Discover areas of heat differences
Can’t see but skin can sense.

21. A thermogram can be used to diagnose problems in a utility line.

22. More Thermograms
What color is showing cooler temperatures?

23. Visible Light The only part of the spectrum the human eye can see.
Each color of light corresponds to a different range of wavelengths.

24. How to remember order Red part of visible light it towards Infrared
Violet part of visible light is towards ultraviolet

25. Ultraviolet Rays Uses in health and medicine, and in agriculture.
helps your skin produce vitamin D
used to kill microorganisms
Treats jaundice in newborn
help plants grow.
Negative: Can cause skin
cancer and blindness in
humans

26. X-rays
Used in medicine, industry, and transportation to make pictures of the inside of solid objects.

27. I can see that!

28. Gamma Rays
Used in the medical field and in industrial situations as an inspection tool.
used to make pictures of the human brain
used in radiation therapy to kill cancer cells
used to check pipes by taking pictures to look for rusting, cracks, or other signs of damage.

29. Electromagnetic Spectrum You will make a chart similar to this but far more detailed.

30. Keep in mind
The electromagnetic spectrum can be expressed in terms of energy, wavelength, or frequency.
Frequency is measured in cycles per second (which is called a Hertz)
Wavelength is measured in meters
Energy is measured in electron volts.

31. Let’s compare them.

32. 18.3 Behavior of Light

33. How does light do that?
When light strikes a new medium, the light can be
Reflected
Absorbed
Transmitted.

34. Reflection
Regular – light waves hit a smooth surface

35. Reflection
Diffuse – light waves hit a rough surface and reflects light in many different directions.

36. Regular (same as Specular)

37. How does light do that? When light is transmitted, it can be Refracted
Polarized
Scattered.

38. Refraction
Light refracts (or bends) when it moves from one medium to another.
What are the 2 mediums shown here?

39. Polarization
A vertical polarizing filter blocks light that is horizontally polarized.

40. Polarization
A horizontal polarizing filter blocks light that is vertically polarized.

41. Polarization Put them together and almost ALL light is blocked out.
View Clip

42. Scattering Light is redirected as it goes thru a medium.
Blue, green, and yellow wavelengths of sunlight are heavily scattered in certain weather conditions.
What color is left?

43. The Color of the Sun

44. The “science” behind it
Description: at sunrise and sunset the sun is yellow, orange or red
Physical process: Rayleigh scattering by air molecules and fine dust particles.
Explanation: on clear days only the blue light is scattered away, on hazy days the yellow and the orange wavelengths are also scattered and only the red remains in the direct solar light.
Conclusion: Red sunsets suggest that there is dust in the air (pollution, haze over the ocean, volcanic activity, dust storms).

45. The Timing of the Sunset & Sunrise
We see the sun before it actually rises above the horizon and after it sets below the horizon.

46. Twilight

47. Flattening of the Sun’s Disk at Sunset
Green flash

48. Your thinking, “Ms. Lolich first the Hulk and now this?”
Green Flash?
Your thinking, “Ms. Lolich first the Hulk and now this?”

49. Green Flash They are usually seen at an unobstructed horizon, such a
Higher frequency light (green/blue) curves more than lower frequency light (red/orange), so green/blue rays from the upper limb of the setting sun remain visible after the red rays are obstructed by the curvature of the earths over the ocean.

50. Development of Green Flash

51. A larger than usual green flash in Santa Cruz

52. Stages of a green flash

53. Quiz: Regular or Diffuse?

54. As the wavelength decreases from the red end of the spectrum to the violet end, what happens to the frequency?
It remains constant.
It increases.
It decreases.
It is impossible to predict what will happen.

55. As the wavelength decreases from the red end of the spectrum to the violet end, what happens to the frequency?
It remains constant.
It increases.
It decreases.
It is impossible to predict what will happen.

56. The End