Intro to light - Flame Test

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Intro to light - Flame Test

• Can be used to identify elements.
• Energy (heat) is used to excite electrons in an
  atom.
• Electrons temporarily move from ground state
  (where they prefer to be) to excited state (a
  high energy level).
• As electron returns to ground state, atom emits
  energy in the form of light.

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Gulp!!!
Burp!!
Photon
Shake!!
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Electromagnetic Radiation(light)

• Produced by changing electric and magnetic fields
• Can be thought of as both a particle and a wave
  (wave-particle duality)
• Does NOT require a medium
• Transverse

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HOMEWORK
Mechanical waves
Electromagnetic waves
Read pgs. 500, 532, 533
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Electromagnetic Waves

• Homework Assignment
• Read pg. 500, 532, 533
• Make a double bubble map to compare and contrast
  electromagnetic waves to mechanical waves.

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Light as a Wave

• When we treat light as a wave, it has the
  properties of any other wave
• Wavelength
• Frequency
• Speed
• These properties are related just like they are
  with mechanical waves.
• What is the formula?

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Electromagnetic RADiation

• The Sun is the source of EM radiation on Earth
• Speed remains the same all EM waves travel at
  the speed of light
• 3.00 x 108 m/s

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Practice Problems

• What is the wavelength of an electromagnetic wave
  that has a frequency of 4.03x1014 Hz?
• 2. What is the frequency of an electromagnetic
  wave that has a wavelength of 3 m?

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Electromagnetic Spectrum

• When we think of light as a wave, we discover
  that electromagnetic radiation (light) can come
  in many forms. These forms depend on the
  wavelength and frequency of the light.
• Electromagnetic waves of different
  frequency/wavelength fall onto different places
  on the electromagnetic spectrum.

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Electromagnetic Spectrum
Left to Right wavelength decreases, frequency
increases
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Electromagnetic Spectrum
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Radio Waves

• Used in radio and television transmission.

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microWaves

• Used in microwave appliances
• Radar waves are also
• a form of microwaves

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Infared waves

• Show the amount of thermal energy (heat) a
  particular object has.
• Heat or Night Vision

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Visible Light waves

• Waves our eyes are capable of seeing

R O Y G B I V
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Ultraviolet Waves

• First potentially harmful form of EM radiation
• Overexposure can lead to skin cancer

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X-Rays

• Used in the medical field to look inside the
  human body

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Gamma Rays

• Highest energy form of EM radiation
• Hardest radiation to be protected from
• Used in treatment of cancer (radiationtreatment)

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What is giving off radiation?

• By studying and displaying the em radiation given
  off by stars, scientists can determine the
  chemical composition of those stars among other
  things.

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Spectrum/Spectra

• Spectrum ? to made a display out of something
• In astronomy, we display radiation using
  spectroscopes (bend light to see various
  wavelengths being emitted)
• Each element produces a set of characteristic
  emission lines

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• From spectral lines astronomers can determine not
  only the element, but the temperature and density
  of that element in the star. The spectral line
  also can tell us about any magnetic field of the
  star. The width of the line can tell us how fast
  the material is moving. We can learn about winds
  in stars from this. If the lines shift back and
  forth we can learn that the star may be orbiting
  another star. We can estimate the mass and size
  of the star from this. If the lines grow and fade
  in strength we can learn about the physical
  changes in the star. Spectral information can
  also tell us about material around stars. This
  material may be falling onto the star from a
  doughnut-shaped disk around the star called an
  accretion disk. These disks often form around a
  neutron star or black hole. The light from the
  stuff between the stars allows astronomers to
  study the interstellar medium (ISM). This tells
  us what type of stuff fills the space between the
  stars. Space is not empty! There is lots of gas
  and dust between the stars. Spectroscopy is one
  of the fundamental tools which scientists use to
  study the Universe.

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Spectra

• Continuous
• A luminous solid or liquid emits a continuous
  spectrum of all wavelengths. It has no lines in
  it.

• Discrete

Emission When hot gas is emitted its own light
Absorbtion When light from a brigher source is
shone through it
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Signatures of elements
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Sun Spectrum