Download Electromagnetic Radiation

2/2/2015
Electromagnetic
Radiation
Ch 4 Intro & 4.1
Electromagnetic Radiation
(EMR)
• A form of energy
emitted by charged
particles that exhibits
a wave-like behavior
as it travels through
space
• This energy is created
by moving electric
and magnetic fields
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EMR is a wave
• Waves have a wavelength and frequency, and
these are used to classify the 7 types of EMR.
These waves
travel at
3.0 x 108 m/s
More later
when we get
to the math
The Wave-Particle Duality
• Many experiments
show EMR as having
properties of an
actual particle (called
a photon).
• EMR acts as both at
times, but we will
focus here on its
wave properties
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What does an EM wave look
like?
• Any moving charge (ex. electron moving around
a proton) has an electric field, and this electric
field induces a magnetic field perpendicular to
the magnetic field (Faraday’s Law of Induction).
The Electromagnetic Spectrum
The arrangement of electromagnetic waves from lowest
to highest frequency (know these in order)
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1. Radio Waves
• Lowest frequency,
longest wavelength
(>30 cm) EMR
• Because they easily
travel around objects
they are used to
transmit information
long distances
• Aren’t significantly
distorted by the
atmosphere
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Uses of Radio Waves
• The Federal
Communications
Commission (FCC)
licenses portions of the
radio (& microwave)
spectrum throughout
the US for TV, radio,
wireless internet, cell
phones, etc.
• SETI
2. Microwaves
• 30cm – 1mm
wavelength
• These can penetrate
weather disturbances,
making the useful in
the transfer of
information.
• Ex. Data transmission,
satellite
communication, cell
phone signaling
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The Microwave Oven
• EM waves are emitted
at a frequency of 2.45
GHz.
• The electric field of
these waves applies a
force to polar water
molecules, accelerating
them.
• As liquid H2O molecules
collide, they transfer KE
Radar
• An object detection
system that uses
microwaves to
determine an objects
position, altitude,
speed, etc.
• Its usage was a major
reason the Allies won
WWII.
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Doppler Radar
3. Infrared Light
• 1mm – 700 nm
• Includes most
thermal radiation
emitted by objects
• Ex. Hot coals
• The majority of our
energy from the sun
is in this form
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Thermal Imaging
• Converts infrared
light into visible light
to amplify images in
low-light situations
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4. Visible Light
• 700 - 380 nm
• Consists of all EMR
visible to the human
eye
• Know ROY G BIV
(longest to shortest
wavelengths of light)
• More later
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5. Ultraviolet Light
• 380 – 10 nm
• Most UV rays produced by the sun are blocked
by atmospheric gases (ozone primarily), though
the ones that get through cause suntans,
sunburn, & skin cancer
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What is the ozone layer?
• It is a layer of high*
concentrations of O3
that filters out most
types of UV light
• UV-A: filters little
• UV-B: filters a lot
• UV-C: filters all
• *6 ppm vs 0.6 ppm
Where is the Ozone Layer
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What causes the hole?
• CFC’s used as aerosol propellants & refrigerants
are known to break down atmospheric ozone
UV light damages DNA
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How’s it doing?
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UV light’s damaging properties
can be useful
6. X Rays
• 10 nm – 0.01 nm
• High-energy rays
produced by electrons
famous for their ability
to penetrate many
materials.
• Many uses, though
carcinogenic
• CT scans attributed
to 0.4% of cancers
• 40% lifetime risk w/o
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7. Gamma Rays
• <0.01 nm
• These highest energy
waves come from
nuclear reactions
• Ex. Radioactive
decay
• Ex. Stars
• They can kill cells,
which is why they are
used in cancer
radiation treatments
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Math Time!
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Electromagnetic radiation propagates through space as a
wave moving at the speed of light.
c = νλ
c = speed of light, a constant (3.00 x 108 m/s)
ν = frequency, in units of hertz (hz, sec-1)
λ = wavelength, in meters
The energy (E ) of electromagnetic radiation is directly
proportional to the frequency (ν) of the radiation.
E = hν
hν
E = Energy, in units of Joules (kg·m2/s2)
h = Planck’s constant (6.626 x 1010-34 J·s)
ν = frequency, in units of hertz (hz
(hz,, sec-1)
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