Electromagnetic Radiation

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Electromagnetic Radiation
Electromagnetic Radiation or EMR is radiant
energy produced by accelerating particles.
There are many forms of EMR distinguished by
their wavelength, frequency and source. Visible
light is a very small portion of the
electromagnetic spectrum. All EMR travels at the
same speed (in a vacuum) the speed of light, c
3.00 x 108 m/s. EMR can be observed either
directly (from the source, i.e. a light bulb) or
indirectly (as reflected or transmitted
radiation, i.e. light reflecting off an object).
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Historically, three different models have been
used to explain the common properties of all
types of EMR. Particle model very simplistic,
but more popular EMR is a stream of tiny
particles, each having mass, momentum and the
ability to be electrically charged Wave model
put forth by Christiaan Huygens (1600s) EMR is a
stream of transverse waves. Unlike water waves,
EMR does not require a medium to move
through. This model became more popular after
Thomas Young and his double slit experiment which
showed that a beam of light shone through two
slits results in an interference pattern. (see
pg. 640) This meant light had to be a wave.
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Both the particle model and the wave model are
supported by scientific evidence, which led to a
third model Quantum model accepted model
today In 1900, Max Planck introduced the idea of
a quanta of energy. He suggested energy could
only be distributed in discrete packets or
values, it was not a continuous quantity. In
1905, Einstein used Plancks idea to propose that
light is emitted in quantized (discrete packets)
particles called photons. The quantum model of
light combines elements from both previous
models EMR is discrete bundles of energy where
each photon is a particle that has wave
characteristics.
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Maxwells Electromagnetic Theory In 1864 James
Clerk Maxwell provided a synthesis of all
electromagnetic phenomenon. This synthesis
included four equations, called Maxwells
Equations. Two of Maxwells equations suggested
that a changing electric field produces a
changing magnetic field and a changing magnetic
field produces a changing electric field and
?E??B??E??B?... He showed that once you started
up one of these waves it would self-propagate
continue on its own it was self-creating. He
predicted that a changing electric field would
initiate an electromagnetic wave.
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The changing magnetic field is always
perpendicular to the changing electric field and
both fields are perpendicular to the direction of
wave propagation.
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• Electric and magnetic fields created this way
• are always perpendicular to each other
• keep reversing direction
• hit maximums and minimums at the same time in
  phase
• involve an oscillating charge
• As the electric field increases, so does the
  magnetic field as one shrinks, so does the other

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• Maxwells Predictions
• EM waves are all created by accelerating/oscillati
  ng charges.
• The frequency of the EM wave will be the same as
  the frequency of the oscillation of the charge.
• All EM waves travel at 310 740 000 m/s (very
  close to the actual value of 3.00 x 108 m/s)
• All EM waves obey the universal wave equation,
  v f?, where f frequency in Hertz, ?
  wavelength in metres, and v c speed of light
  in a vacuum.
• Changing electric and magnetic fields and
  direction of propagation will always be
  perpendicular.
• All EM waves have the same properties as
  transverse waves interference, diffraction,
  refraction, and polarization.

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In 1887 Heinrich Hertz generated the first
observed EM waves, using a spark gap to create
the oscillating charge. He was able to
demonstrate many properties consistent with
properties of light (reflection, refraction,
diffraction, etc.) as well as show that his EM
waves traveled at the speed of light. In 1889,
the first radio transmission occurred across the
English Channel. In 1901, the first radio
transmission across the Atlantic Ocean
occurred. Production of EMR is one of the
greatest achievements of the 19th century
leading to many of the technologies we enjoy
today.
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• TYPES OF EMR
• AC Power created by AC current
• frequency 60 Hz wavelength 5 X 106 m very
  weak cause static in electronic devices
• Radio oscillating changes in wire or crystal
• frequency 104 109 Hz wavelength 10-1 104 m
• AM radio transmitted by modulating the amplitude
  of a carrier wave
• FM radio transmitted by modulating the frequency
  of a carrier wave
• includes TV, AM, FM, radar, cell phones,
  cordless phones
• easy to generate

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• Microwaves - oscillating charges in electronic
  devices
• frequency 109 1012 Hz wavelength 10-4 10-1
  m as f is increasing, ? is going down long
  range transmission of telecommunication info.
  cooking
• can be aimed at their destination
• Infrared - electron transitions within atoms
• frequency 1012 1014 Hz wavelength 10-6
  10-4m related to heat
• use to keep fries warm and to see in the dark

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• Visible electron transitions within atoms,
  higher energy big jumps inside the atom
• frequency 4 X 1014 8 X 10 14 Hz wavelength
• 350 700 nm
• light which we see (ROY G BIV)
• cause photochemical reactions eg. Film
• Ultraviolet even higher energy e- transitions
• frequency 1015 1017 Hz wavelength 10-9
  10-7 m
• just past violet on the visible spectrum
  cause photochemical reactions in skin pigment,
  fluorescence of some chemical substances.

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• X-rays rapid deceleration of high energy (high
  v) e-
• frequency 1017 1020 Hz wavelength 10-12
  10-9 m
• able to pass through less dense materials, i.e.
  flesh
• many medical uses, esp. imaging of bones
  teeth
• safe in low doses
• Gamma rays come from radioactive decay of atoms
• frequency 1020 1024 Hz wavelength 10-16
  10-12 m
• decay of nuclei, whether in natural
  radioactivity or
• man-made accelerators
• treatment for cancer in localized tumours
• dangerous radiation exposure is very dangerous