1. The Electromagnetic Spectrum and Light

2. Electromagnetic Waves
Electromagnetic waves- transverse waves consisting of changing electric and magnetic fields
Carry ENERGY from place to place
Different from mechanical waves…how?

3. How are EM Waves produced?
An electric field exerts forces on charged particles
Electric fields are produced by
charged particles
changing magnetic fields
A magnetic field produces magnetic forces
Magnetic fields are produced by
magnets
changing electric fields
vibrating charges

4. How do EM waves travel?
As the two fields regenerate each other, their E travels in the form of a wave.
EM waves DON’T need a medium!!!
Can travel through a vacuum (=empty space) OR through matter
EM radiation – the transfer of E by EM waves traveling through matter or across space.

5. What is faster…speed of sound or light?
Light travels much faster than sound. For example:
Thunder and lightning start at the same time, but we will see the lightning first.
2) When a starting pistol is fired we see the smoke first and then hear the bang.

6. Speed of Light
First accurate estimations were in 1926 when Albert Michelson completed his experiment in California.

7. Speed of Light c = 3.00 x 108 m/s Or 300,000,000 m/s
Light (and all EM waves) travel the same speed in a vacuum…
c = 3.00 x 108 m/s
Or 300,000,000 m/s
(compared to ~ 340 m/s)
That’s 8 times around the earth in 1 second!!!!

8. l and frequency EM waves vary in l and frequency c = l * frequency
Since the speed of light (c) is always x 108 m/s, you can always calculate l from frequency and vice versa.

9. Wave or Particle???
EM radiation sometimes behaves like a wave, and sometimes like a stream of particles.
There is evidence for both theories...
That’s called wave-particle duality
In some experiments, the wave model works best.
In other experiments, the particle model works best.
Thus, we use both

10. Electromagnetic
Radiation
Light
Photons

11. Wave… Double Slit Experiment Interference is a property of waves!
Pass light through two slits and an interference pattern is observed
Interference is a property of waves!

13. Particle… Photons- particles of light
Photoelectric Effect
Light shown on a metal can cause electrons to be emitted from the metal
Photons- particles of light
The greater the frequency of an EM wave, the more E each of its photons has

15. Intensity
Intensity- the rate at which a wave’s energy flows through a given unit of area…basically, it is brightness of light.
As you leave the source of light, does intensity increase or decrease?

16. Farther from the source, the photons spread out over a larger area, and intensity decreases.

17. The Electromagnetic Spectrum

18. The Waves of the Spectrum
What happens when you put a prism in front of a window?

19. The EM Spectrum
EM spectrum- the full range of frequencies of EM radiation
How many different types of EM waves can you think of?
EM Spectrum includes:
Radio waves
Infrared rays
Visible light
UV rays
X-rays
Gamma Rays

22. Television
Shorter than radio, also used to carry messages (pictures & sound) to our TV sets.
We can sense the TV waves around us with our televisions.

23. Microwave Emitted by: Detected by Gas clouds collapsing into stars
Microwave Ovens
Radar Stations
Cell Phones
Detected by
Microwave Telescopes
Food (heated)
Cell phones
Radar (systems)

24. Infrared (Heat or Thermal) Are you a source of infrared? YES you are!
Emitted by
Sun and stars (Near)
TV Remote Controls
Food Warming Lights (Thermal)
*Everything at room temperature or above,=HEAT
Detected by
Infrared Cameras
TVs, VCRs,
Your skin

25. Visible Each color is a different size wave
Visible Each color is a different size wave. Red the longest & violet the shortest
Emitted by
The sun and other astronomical objects
Laser pointers
Light bulbs
Detected by
Cameras
Human eyes
Plants (red light)
Telescopes
RoyG.Biv

26. Ultraviolet Sunburn / black light
He can get skin cancer!
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)

27. X-ray Emitted by Detected by Astronomical objects X-ray machines
CAT scan machines
Radioactive minerals
Airport luggage scanners
Detected by
Space based X-ray detectors
X-ray film

28. Gamma Ray (Short electromagnetic waves but more energetic)
Emitted by
Radioactive materials
Exploding nuclear weapons
Solar flares
Detected by Geiger counters
Gamma detectors and astronomical satellites
Medical imaging detectors

29. COSMIC Rays (The highest energy waves and the deadliest)
Cosmic rays come from deep space and can pass through the Earth.

30. Behavior of Light

31. Light and Materials
When you are looking at things, anything, what you are really seeing is light.
We can’t see through walls because light doesn’t pass through walls.

32. We see things because they reflect light into our eyes:
Homework

33. Light and Materials, ctd.
How light behaves when it strikes an object depends on many factors, including the material the object is made of
Materials can be translucent, transparent, or opaque.

34. Transparent objects- Translucent- Opaque- No scattering
Color transmitted is color you see and all other colors are absorbed
Translucent-
Light is scattered and transmitted some
Opaque-
Light is either totally reflected or absorbed
Color of opaque objects is color it reflects

35. Interactions of Light
When light strikes a new medium, the light can be reflected, absorbed, or transmitted.
When light is transmitted, it can be refracted, polarized, or scattered.

36. Reflection Mirror Reflection from a mirror: Normal Angle of incidence
Incident ray
Reflected ray
Angle of incidence
Angle of reflection
Mirror

37. Angle of incidence = Angle of reflection
The Law of Reflection
Angle of incidence = Angle of reflection
The same !!!

38. Clear vs. Diffuse Reflection
Smooth, shiny surfaces have a specular reflection:
Rough, dull surfaces have a diffuse reflection
Diffuse reflection is when light is scattered in different directions

39. Using mirrors
Two examples:
2) A car headlight
1) A periscope

40. Refraction
The bending of light waves as they pass from one medium to another
Results in mirages, which are false or distorted images

41. Inferior Mirages:
formed when the air near the ground is very warm compared to the air just above it.

42. Polarized
Polarized light is light that all vibrate in the same plane (or direction!)

43. Scattering Light is redirected as it passes through a medium.
This is responsible for our red sunsets!

44. Color

45. We can demonstrate this by splitting white light with a prism
White light- not a single color; it is made up of a mixture of the seven colors of the rainbow
We can demonstrate this by splitting white light with a prism
This is how rainbows are formed: sunlight is “split up” by raindrops .

46. Red
Orange
Yellow
Green
Blue
Indigo
Violet

47. Adding Colors
White light can be split up to make separate colors. These colours can be added together again
The primary colors of light are red, blue and green:
Adding blue and red makes magenta (purple)
Adding blue and green makes cyan (light blue)
Adding red and green makes yellow
Adding all three makes white again

48. Only red light is reflected
Seeing Color
The color an object appears depends on the colors of light it reflects
For example, a red book only reflects red light:
Homework
White light
Only red light is reflected

49. A white hat would reflect all seven colors:
A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue):
Purple light
A white hat would reflect all seven colors:
White
light

51. Testing
Color Blind Tests

52. Optical Illusions

65. Which circle in the middle is bigger?

66. Do you see gray areas in between the squares
Do you see gray areas in between the squares? Now where did they come from?

67. If you continue to focus on the sign in the centre of the image you will notice that the circle of violet circles will soon disappear completely, and you will see only the green spot (which is actually violet)

68. LIGHT & ITS USES: Lenses
Convex lenses
Thicker in the center than edges.
Lens that converges (brings together) light rays.
Forms real images and virtual images depending on position of the object
The images formed are upside down

69. LIGHT & ITS USES: Lenses
Focal Point
Object
Convex Lenses
Ray Tracing
Two rays usually define an image
Ray #1: Light ray comes from top of object; travels parallel to optic axis; bends thru focal point.
© 2000 D. L. Power
Lens

70. LIGHT & ITS USES: Lenses
Ray #1
Convex Lenses
Ray Tracing
Two rays define an image
Ray 2: Light ray comes from top of object & travels through center of lens.
© 2000 D. L. Power
Ray #2

71. LIGHT & ITS USES: Lenses
© 2000 D. L. Power
Concave lenses –
Lens that is thicker at the edges and thinner in the center.
Diverges light rays
All images are upright and reduced

72. Vision Retina Rods Cones The eye is a convex lens
Lens refracts light to converge on the retina and then nerves transmit the image
Rods
Nerve cells in the retina. Very sensitive to light & dark
Cones
Nerve cells help to see light/color

73. PARTS OF EYE CONTINUED…
Rods – responsible for black and white vision and detection of motion.
Cones – Seeing in color and visual acuity. We have three types of cones: cones that see red, cones that see blue, and cones that see green.

74. How You See
Near Sighted – Eyeball is too long and image focuses in front of the retina
Far Sighted – Eyeball is too short so image is focused behind the retina.

75. LIGHT & USES: Optical Instruments
LASERS
Holography – Use of Lasers to create 3-D images
Fiber Optics – Light energy transferred through long, flexible fibers of glass/plastic
Uses – Communications, medicine, t.v. transmission, data processing.

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