Electromagnetic Electromagnetic SpectrumSpectrum

© 2000 Microsoft Clip Gallery

Modulating Radio Modulating Radio WavesWaves

Modulation - variation of amplitude or frequency when waves are

broadcastAM – amplitude modulation

Carries audio for T.V. BroadcastsLonger wavelength so can bend

around hillsFM – frequency modulation

Carries video for T.V. Broadcasts

LIGHTLIGHT

Chap 16Light modelsIllumination – inverse square lawNature of light phenomena

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

16.116.1 LIGHT: What Is It?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

16.1: Light Model16.1: Light Model

How can you model the path of light through How can you model the path of light through air?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.

16.1 Sources of light 16.1 Sources of light

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

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.

16.1 Sources of light 16.1 Sources of light

Example: Fluorescent lampLaser

TV screenLEDs (light-emitting diodes)

computer monitors, chemical reactions as Halloween light sticks

and fire-flies, radioactivity as in luminous paints

luminescence is produced when an electron releases some of its energy to EM radiation, not an entire atom.

16.1 Sources of light 16.1 Sources of light

Illuminated sources are visible to you Illuminated sources are visible to you because …because …

Do “Light and Matter” WS page 1-2

16.1 Sources of light 16.1 Sources of light

16.1 How can we calculate 16.1 How can we calculate light?light?

Luminous flux (P) – the rate at which light energy [lm]

Example: 100 W incandescent bulb emits app. 1750 lm.

illuminance (E) – a measure of how much luminous flux is spread

over a given area. [Lx]Inverse-square law

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

16.1 How can we calculate 16.1 How can we calculate light?light?

2

4rE

PI

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.

Electromagnetic Electromagnetic SpectrumSpectrum Visible Spectrum – Light we can

see Red, Orange, Yellow, Green,

Blue, Indigo, & Violet.Largest to Smallest Wavelength.

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

Spectrum

Color by addition of Color by addition of light 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.

Complementary colors

Color by addition of Color by addition of light light

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.

Color by subtraction of light

Quick QuizTest your understanding of

subtraction

Color by subtraction of light

Answer1. (Red + Blue) - Blue = Red2. Red = red 3. Blue - Blue = Black

Color by subtraction of light

Quick QuizTest your understanding of

subtraction

Color by subtraction of light

Polarization of lightThe 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.

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

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.

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

Doppler effect in light:Doppler effect in light:

Redshift and BlueshiftDoppler’s shift is of great use in

astronomy. A light source moving away from

the observer would provide .

It is called Redshift.

Doppler effect in light: Redshift and Blueshift

• When the light source is moving toward the observer, then

It is called Blueshift

How You SeeHow You SeeRetina –

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