1 EM Waves Intro

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Transcript 1 EM Waves Intro

Warm - Up
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
Electromagnetic Radiation
(EM Waves)
Faraday and Ampere’s Laws
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
Moving Charges
Why we need antennae
Sources of radiation
Radio Antennae
X-Ray Machines
Standard wave properties
 Amplitude
 Wavelength
 Frequency
Light Speed
The speed of light is a universal
It is independent of the frame of
299,792,458 m/s (in a vacuum)
Found experimentally confirmed
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
Rate at which light is emitted from a
source (measured in lumens [lm])
Illuminance – illumination of a
surface (lm/m2 = lux)
Inverse square relationship
Double the distance from a light
source, and you decrease by ¼ the
Particle nature of light
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
Photo electric effect
Einstein thought light could be
Called light quanta: photons
Photon energy depends on the
frequency of the photon
h = Planck’s Constant = 6.6 x 10-34 J s
 F = frequency
Work 16.1 – Pg 389
7, 10-12, 16,
20,21, 31-33, 41)
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
See P 374