1. Chapter 22—The Nature of Light
Material on the Final Exam

2. Section 1—What is Light? Objectives
How is light an electromagnetic wave?
Explain how you could calculate distances traveled by light using the speed of light
Explain why light from the sun is important

3. Light: An Electromagnetic Wave
Light travels as a wave
Light does not need matter to travel
Light is an electromagnetic wave
Electromagnetic waves are waves that consist of electric and magnetic fields that vibrate at right angles to each other

4. Electromagnetic Wave

5. Electric and Magnetic Fields
An electric field surrounds every charged object
A magnetic field surrounds every magnet

6. How EM Waves are Produced
Produced by the vibration of an electrically charged particle
Creates electric field
Field starts vibrating
Creates magnetic field
Carries energy

8. The speed of light Fastest thing known to science In a vacuum
300,000,000 m/s
300,000 km/s
Slows down in matter
Faster than sound

9. The speed of light
We can use the speed of light to find how far it travels
Formula
SI units for speed: m/s
SI units for distance: m
SI units for time: s
Speed = distance
time

10. Math Practice Math Practice You try!
The distance from Earth to the moon is 384,000 km. Calculate the time it takes for light to travel that distance.
You try!
The distance from the sun to Venus is 108,000,000 km. Calculate the time it takes for light to travel that distance.

11. Math Practice Math Practice You try!
It takes 2595 seconds (43 min) for light from the sun to reach Jupiter. How far away is Jupiter?
You try!
The alpha centauri system has two stars. If it takes 11470s for light to reach one star to the other, how far apart are they?

12. Light from the Sun Light is a major energy source for our planet
Plants use it to make food
Animals eat these plants
Fossil fuels store solar energy from the past

13. Section 1—What is Light? Objectives
How is light an electromagnetic wave?
Explain how you could calculate distances traveled by light using the speed of light
Explain why light from the sun is important

14. Section 2—The electromagnetic Spectrum
Objectives
Identify the two ways that EM waves differ from each other
Describe some uses for radio waves and microwaves
List examples of how infrared waves and visible light are important in your life
Explain how ultraviolet light, X rays, and gamma rays can be both harmful and helpful

15. Characteristics of EM waves
Light is only a teeny part of all EM waves
The electromagnetic spectrum is the entire range of EM waves
Divided by wavelength and frequency

17. Radio Waves Longest wavelengths (30+ cm) Lowest frequencies
Used for broadcasting radio signals
Modify frequency or amplitude (height) of wave
AM and FM radio

18. Radio Waves FM versus AM Radio AM has longer wavelengths
AM bounce off atmosphere
FM less affected by electrical “noise”
Why FM sounds better

19. Radio waves and Television
TV signals carried by radio waves
Shorter wavelengths than radio
Higher frequencies than radio
Change frequency and amplitude
Sent to satellites to amplify signal

20. Microwaves
Shorter wavelengths (1mm-30cm) and higher frequencies than radio
Microwave ovens, Radar and communication

21. Radar From microwaves Radio detection and ranging
Finds speed and location of object
Sends waves that bounce off items

22. Infrared Waves
Shorter wavelengths (700 nm to 1mm) and higher frequencies than microwaves
“Warm” feeling on sunny day
Heat
Invisible for us, but can be detected--thermogram

24. Visible Spectrum
Narrow range of wavelengths and frequencies that humans can see
White light is the combination of all colors of light

25. Ultraviolet Light
Shorter wavelengths (60-400nm) and higher frequencies than visible light
Both good and bad for your body

26. Ultraviolet Light Good Effects Bad Effects Kill bacteria on food
Sterilize surgical tools
Helps body make vitamin D
Helps with calcium absorption
Bad Effects
Sunburn
Skin cancer, wrinkles, eye damage
Protected by ozone, clothing and sunscreen

27. X rays and Gamma Rays X rays Gamma rays .001nm-60nm wavelength
Medical field
Kill cells
Lead aprons
Airport security
Gamma rays
Shortest wavelengths (<0.1nm) and highest frequency
Penetrate almost all materials
Treat cancer
Kill cells
Kill bacteria on food

28. Section 2—The electromagnetic Spectrum
Objectives
Identify the two ways that EM waves differ from each other
Describe some uses for radio waves and microwaves
List examples of how infrared waves and visible light are important in your life
Explain how ultraviolet light, X rays, and gamma rays can be both harmful and helpful

29. Section 3—Interactions of Light Waves
Objectives
Describe how reflection allows you to see things
Describe absorption and scattering
Explain how refraction can create optical illusions
Explain how refraction can separate white light into colors
Compare constructive and destructive interference of light

30. Reflection Reflection is when light waves bounce off an object
EX: mirror
The Law of Reflection states that the angle of incidence is equal to the angle of reflection
The angle it comes in is the same angle it goes out

32. Types of Reflection
Regular Reflection is when all light beams are reflected at the same angle
Smooth surfaces
Diffuse Reflection is when light beams reflect at many different angles
Not smooth

33. Light Source or Reflection?
Luminous objects produce visible light
Light source
Illuminated objects are visible objects that are not a light source
Due to the light around it (reflection

34. Absorption and Scattering
Absorption is the transfer of energy carried by light waves to particles of matter
Air absorbs some energy
Why a flashlight dims
Farther the light source, the more light that gets absorbed

35. Absorption and Scattering
Scattering is an interaction of light with matter that causes light to change direction
All directions
See objects outside beam
WHY THE SKY IS BLUE!

36. Refraction
Refraction is the bending of a wave as it passes at an angle from one substance to another

37. Refraction Why does refraction happen
Light travels at different speeds when it goes through different things

38. Refraction When light switches materials, it speeds up or slows down
This changes the angle

39. Diffraction
Diffraction is the bending of waves around barriers or through openings
Depends on wave size
Depends on barrier size

40. Diffraction and Wavelength
Small wavelength for light!
Does not bend much unless opening is even smaller
Why light does not bend around corners

41. Interference
Interference is a wave interaction that happens when two or waves overlap
Can brighten: constructive
Can dim: destructive

42. Constructive v. destructive interference

43. Section 3—Interactions of Light Waves
Objectives
Describe how reflection allows you to see things
Describe absorption and scattering
Explain how refraction can create optical illusions
Explain how refraction can separate white light into colors
Compare constructive and destructive interference of light

44. Section 4—Light and Color
Objectives
Name and describe the three ways light interacts with matter
Explain how the color of an object is determined
Describe color addition and color subtraction

45. Light and Matter When light strikes objects, it can be Reflected
Absorbed
Transmitted

46. Reflection, Absorption,Transmission
Reflection is when light bounces off an object
Absorption is when light energy is transferred to matter
Transmission is the passing of light through matter

47. Types of Matter
Transparent matter is matter through which visible light is easily transmitted
Ex: glass, plastic wrap

48. Types of Matter
Translucent matter transmits light but also scatters it
Ex: frosted glass, wax paper

49. Types of Matter
Opaque matter is matter that does not transmit any light
Ex: Aluminum foil, a book, wood

50. Colors of Objects
Color is about the reflection of light off materials that hits your eyes

51. Colors of objects Translucent objects Opaque objects
The colors you see are the colors that are transmitted
Opaque objects
The colors you see are the colors that are reflected
White = ALL colors reflected
Black = ALL colors absorbed

52. Mixing colors of light Only need 3 colors to make white light
Red
Green
Blue
Called primary colors of light

53. Color addition Combining colors of light is called color addition
Mixing two primary light colors makes secondary light colors

54. Colored Television
Television has color because each “dot” has a group of red, green, and blue dots
Different combinations give us color

55. Mixing colors of pigment
A pigment is a material that gives a substance its color by absorbing some color of light and reflecting others
Primary pigments
Magenta
Yellow
Cyan

56. Color subtraction
Mixing pigments results in more colors being absorbed or taken away—color subtraction

57. Section 4—Light and Color
Objectives
Name and describe the three ways light interacts with matter
Explain how the color of an object is determined
Describe color addition and color subtraction