3 Modulating Radio Waves Modulation - variation of amplitude or frequency when waves are broadcastAM – amplitude modulationCarries audio for T.V. BroadcastsLonger wavelength so can bend around hillsFM – frequency modulationCarries video for T.V. Broadcasts
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 fieldswhich propagate through space, forming anelectromagnetic 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/secSpeed 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 ModelHow can you model the path of light through air?Light is presented as a ray that travels in a straight pathRay 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.NaturalArtificial - man madeIncandescence - the vibration of entire atoms.luminescence involves only the electrons.Luminous source
10 16.1 Sources of lightIncandescent 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 lampLaserTV screenLEDs (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 lightDo “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] candelapage 436 # 1-6
15 ExplainingCommon 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 seeRed, Orange, Yellow, Green, Blue, Indigo, & Violet.Largest to Smallest Wavelength.
17 SpectrumEach 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 QuizTest your understanding of subtraction
22 Color by subtraction of light Answer1. (Red + Blue) - Blue = Red2. Red = red3. Blue - Blue = Black
23 Color by subtraction of light Quick QuizTest your understanding of subtraction