Electromagnetic Radiation

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Electromagnetic Radiation
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Definitions

• Electromagnetic Radiation is energy with wavelike
  characteristics
• Moves at a speed of 3.0 x 108 m/s

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• Wavelength (?) is the distance between identical
  points on successive waves meters
• Frequency (?) is the waves passing per second
  unit is the Hertz (Hz)

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• Each type of radiant energy has its own
  characteristic frequency and wavelength
• Short wavelength then high frequency
• Long wavelength then low frequency

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EM Equation

• c ??
• Yellow light given off by a sodium lamp has a
  wavelength of 589 nm. What is its frequency?
• Radiation of high frequency has more energy than
  that with low frequency

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Quantum Theory

• Rules that govern the gain and loss of energy
  from an object

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Max Planck

• Said energy comes in chunks called quantum
• Energy of the quantum depends on the frequency
• ?E h?
• Plancks constant (h) is 6.63x10-34 J-s

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Energy Lost or Gained

• Total energy lost or gained is a multiple of the
  quantum
• ?Etot nh?
  
  n number of quantum

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Example 1

• Calculate the smallest increment of energy that
  an object can absorb from yellow light with a
  wavelength of 589 nm.

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Example 2

• A laser emits light pulses of frequency of
  4.69x1014 Hz and deposits 1.3x10-2 J on energy
  each pulse. How many quantum of energy is this?

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Photoelectric Effect

• Light shining on certain metals emit electrons
• A minimum frequency of light is necessary
• Albert Einstein explained this effect with
  quantum theory

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• Quantum of light is called a photon
  Ephoton h?
• When photons are absorbed by a metal, energy is
  transferred to the electrons
• If sufficient energy, the electron can overcome
  the attractive forces holding it in the atom and
  escape

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• Amount of energy depends on the freq.
• If freq is too low, not enough energy for
  electron to escape
• If freq is higher than what is needed for
  electron to escape, the extra energy is converted
  into kinetic energy making the electron move
  faster

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• Total energy of photon energy required to free
  electron kinetic energy
• h? EB EK

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Example

• Potassium metal must absorb a wavelength of 540
  nm (green) or shorter in order to emit an
  electron. What will be the kinetic energy of an
  electron if it absorbs 380 nm (UV) light?