Download Preview of Period 3: Electromagnetic Waves – Radiant Energy II

Preview of Period 3: Electromagnetic
Waves – Radiant Energy II
3.1
Radiant Energy from the Sun
How is light reflected and transmitted?
What is polarized light?
3.2
Energy Transfer with Radiant Energy
How can electromagnetic waves transfer
energy and information?
3.3
Radio and Television Broadcasts
What is the difference between AM and FM
broadcasts?
3-1
Solar Cells and the Photoelectric Effect
Solar cells use the photoelectric effect to
produce electricity.
♦ When electrons absorb photons of
electromagnetic radiation, some electrons have
enough energy to escape from their atom and
form an electric current.
♦ Only photons with wavelengths equal to or
shorter than visible light have enough energy
per photon to produce a current.
3-3
Activity 3.1.d: Mirrors and Lenses
How does light reflect off of a plane mirror?
Light box
Mirror
♦ Place a sheet of white paper under the
mirror.
♦ Mark the position of the mirror on the paper
with a straight line.
♦ Draw lines on the paper showing the path of
the light beams at they strike the mirror and
reflect off the mirror.
♦ Use a protractor to compare the angle of
incidence and the angle of reflection of light
striking a mirror.
♦ How are these angles related?
How is light reflected from
concave and convex mirrors?
Focus
A Concave Mirror Focuses
Radiant Energy
A Convex Mirror Spreads
Radiant Energy
How is light transmitted through
concave and convex lenses?
Focus
A Concave Lens Focuses
Radiant Energy
A Convex Lens Spreads
Radiant Energy
An Atom Flourescing
Fluorescence is the absorption of radiant energy and the
re-emission of radiant energy at longer wavelengths.
Photon 1
Electron
Nucleus
Time 1: An ultraviolet light photon is
absorbed by an electron.
Photon 2
Time 3: The electron drops down one
one energy level and emits
one photon of visible light.
Time 2: The electron moves up
two energy levels.
Photon 3
Time 4: The electron drops down
one more energy level and
emits a second photon.
3-6
Information Transfer
Communication is the transfer of information
Transferring information requires …..
♦ a source of information (a person or device)
♦ a signal (the information)
♦ a receiver
♦ modulation (changing) of the signal
Encoding Information
♦ Information must be encoded for transfer.
♦ Encoding modulates the signal in a way
meaningful to the sender and receiver.
♦ Examples of encoded information:
Spoken and written language
Computer languages
Sign language
Morse Code
3-7
Signal to Noise ratio
SNR = average energy in the signal
average energy in the noise
A large signal to noise ratio is better
(Example)
If the average energy in the noise of a
signal is 250 joules and the average energy in
the signal is 750, what is the signal to noise
ratio?
SNR = average energy in the signal = 750 J = 3
average energy in the noise
250 J
3-8
Total Internal Reflection of Light in an
Optical Fiber
Lower Index
of Refraction
Higher Index
of Refraction
Wire
Many of these optical fibers are combined into a cable.
Electromagnetic Radiation Traveling in a
Coaxial Cable
Electromagnetic
Radiation
Coaxial Cable
Central
Wire
Metal
Sheath
3-9
Information Transfer
Radio and TV broadcasts use a carrier wave that is
modulated to encode information.
♦ AM modulates the amplitude (the height) of the
carrier wave.
♦ FM modulates the frequency of the carrier wave.
Amplitude Modulation – AM Radio
AM radio operates on the principle of encoding by modulating the amplitude of
the carrier wave. Figure 3.6 illustrates a carrier wave whose amplitude has been
modulated to encode the signal of a complex sound wave.
Amplitude Modulation
Frequency Modulation