Transcript 1 EM Waves Intro

Warm - Up
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1. How was Spring Break? What did
you do?
2. The School store uses a new
pricing system. A vest costs $20,
socks: $25, a tie: $15 and a blouse
costs $30. Under this system, how
much would a pair of underwear
cost?
Electromagnetic Radiation
(EM Waves)
Faraday and Ampere’s Laws
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Electricity and magnetism operate
via ‘fields’
Ampere-Maxwell law: A changing
Electric field creates a Magnetic field
Faraday’s Law: A changing Magnetic
field creates an Electric field
The created field is perpendicular to
the original field.
How are EM Waves created
Ways to create EM Radiation
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Moving Charges
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Why we need antennae
Sources of radiation
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Microwaves
Radio Antennae
Stars
X-Ray Machines
Uses?
Properties
Standard wave properties
 Amplitude
 Wavelength
 Frequency
Light Speed
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The speed of light is a universal
constant,
It is independent of the frame of
reference.
299,792,458 m/s (in a vacuum)
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Found experimentally confirmed
mathmatically
3 * 108 m/s is good enough
Written as ‘c’
Electromagnetic spectrum
All travel at the same speed but, EM
waves are differentiated by
wavelength, frequency, energy
Flux
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Rate at which light is emitted from a
source (measured in lumens [lm])
Illuminance – illumination of a
surface (lm/m2 = lux)
Illumination
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Inverse square relationship
Double the distance from a light
source, and you decrease by ¼ the
illumination
Particle nature of light
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The wave model of light fails when
we shine light on zinc, which causes
a release of photoelectrons.
Increasing the intensity of the light
does not always cause more
electrons to be released,
Emission depends on frequency
(color)
Photo electric effect
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Einstein thought light could be
quantized
Called light quanta: photons
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Photon energy depends on the
frequency of the photon
E=h*f
h = Planck’s Constant = 6.6 x 10-34 J s
 F = frequency
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Work 16.1 – Pg 389
P389
(1-4,
7, 10-12, 16,
20,21, 31-33, 41)
Homework
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Draw an EM spectrum
Need to have: Wavelength (units
labeled), type of wave, frequency,
examples drawn and labeled, also
which end is low energy, which is
high.
See P 374