2. Electromagnetic Spectrum
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3. Modulating Radio Waves
Modulation - variation of amplitude or frequency when waves are broadcast
AM – amplitude modulation
Carries audio for T.V. Broadcasts
Longer wavelength so can bend around hills
FM – frequency modulation
Carries video for T.V. Broadcasts

4. LIGHT

5. Chap 16 Light models Illumination – inverse square law
Nature of light phenomena

6. 16.1 Illumination What do you know about light? What is light ?
How can you model light beam?
How do you know your model of light is correct?
How can you see things around you?
Light source

7. 16.1 LIGHT: What Is It?
Light is a range of electromagnetic radiation that can be detected by the human eye.
It is as changing electric and magnetic fields
which propagate through space, forming an
electromagnetic wave.
Light is a transverse wave.
EM radiation has a dual nature as both particles and waves.
Speed in vacuum is 300,000 km/sec or 186,000 mi/sec
Speed in other materials - slower in Air, Water, Glass, and etc

8. Ray model of light helps us to study how light interact with matter.
16.1: Light Model
How can you model the path of light through air?
Light is presented as a ray that travels in a straight path
Ray model of light helps us to study how light interact with matter.

9. 16.1 Sources of light Luminous source
Rays of light come from sources of light.
2 types of light sources.
Natural
Artificial - man made
Incandescence - the vibration of entire atoms.
luminescence involves only the electrons.
Luminous source

10. 16.1 Sources of light
Incandescent light is produced when atoms are heated and release some of their thermal vibration as EM radiation.
Example: the sun, fire and light bulbs.
Depending on how hot the material is, the photon released have different energies, and therefore, different colors.

11. 16.1 Sources of light Example: Fluorescent lamp Laser TV screen
luminescence is produced when an electron releases some of its energy to EM radiation, not an entire atom.
Example: Fluorescent lamp
Laser
TV screen
LEDs (light-emitting diodes)
computer monitors,
chemical reactions as Halloween light sticks and fire-flies, radioactivity as in luminous paints

12. Illuminated sources are visible to you because …
16.1 Sources of light
Do “Light and Matter” WS page 1-2

13. 16.1 How can we calculate light?
Luminous flux (P) – the rate at which light energy [lm]
Example: 100 W incandescent bulb emits app lm.
illuminance (E) – a measure of how much luminous flux is spread over a given area. [Lx]
Inverse-square law

14. 16.1 How can we calculate light?
Luminous intensity (I) – the luminous flux that falls on 1 square meter of the inside of 1 m radius sphere. [Cd] candela
page 436 # 1-6

15. Explaining
Common candle emits light with roughly 1 cd luminous intensity. A 25 W compact fluorescent light bulb puts out around 1700 lumens; if that light is radiated equally in all directions, it will have an intensity of around 135 cd. Focused into a 20° beam, it will have an intensity of around 18 000 cd.

16. Electromagnetic Spectrum
Visible Spectrum – Light we can see
Red, Orange, Yellow, Green, Blue, Indigo, & Violet.
Largest to Smallest Wavelength.

17. Spectrum
Each different color of light refracts at different angle.
This uneven refraction causes the white light to be spread into spectrum.

18. Color by addition of light
The white light formed from colored light in variety of way.
Complementary colors - two colors of light that can be combined to make white light.

19. Color by addition of light
Complementary colors

20. Color by subtraction of light
Objects can reflect and transmit light.
Also they can absorb light.
A object not only depends on wavelength present in light that illuminates the object, but also depends on what wavelengths are observed and what wavelengths are reflected.

21. Color by subtraction of light
Quick Quiz
Test your understanding of subtraction

22. Color by subtraction of light
Answer
1. (Red + Blue) - Blue = Red
2. Red = red
3. Blue - Blue = Black

23. Color by subtraction of light
Quick Quiz
Test your understanding of subtraction

24. Color by subtraction of light

25. Polarization of light
The polarization of light is described by specifying the orientation of the wave's electric field at a point in space over one period of the oscillation.

26. 16.2 Polarization
A light wave that is vibrating in more than one plane is referred to as unpolarized light.

27. The electric field may be oriented in a single direction (linear polarization)
Polarized light waves are light waves in which the vibrations occur in a single plane.

28. 6. Liquid crystal display
Light source
Observation
1. Incandescent light
2. Fluorescent light
3. Mirrored surface
4. White paper
5. Black paper
6. Liquid crystal display
7. Two polarizing filter

29. Doppler effect in light: Redshift and Blueshift
Doppler’s shift is of great use in astronomy.
A light source moving away from the observer would provide
It is called Redshift.

30. Doppler effect in light: Redshift and Blueshift
When the light source is moving toward the observer, then
It is called Blueshift

32. How You See
Retina –
Lens refracts light to converge on the retina. Nerves transmit the image
Rods –
Nerve cells in the retina. Very sensitive to light & dark
Cones –
Nerve cells help to see light/color