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Electromagnetic%20Radiation

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Title: Electromagnetic%20Radiation


1
Chapter 6 Electromagnetic Radiation
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Short wavelength --gt high frequency high
energy
  • Long wavelength --gt
  • small frequency
  • low energy

5
The electromagnetic spectrum.
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Which has the longest wavelength?
  1. Infrared
  2. Ultraviolet
  3. X-rays
  4. Radio waves

8
  • Rank the following in order of increasing
    frequency
  •  
  • microwaves
  • radiowaves
  • X-rays
  • blue light
  • red light
  • UV light
  • IR light

9
  • Waves have a frequency
  • Use the Greek letter nu, ?, for frequency, and
    units are cycles per sec
  • All radiation ? ? c
  • c velocity of light 3.00 x 108 m/sec
  • Long wavelength ?small frequency
  • Short wavelength ?high frequency

10
The Wave Nature of Light
  • The product of the frequency, n (waves/sec) and
    the wavelength, l (m/wave) would give the speed
    of the wave in m/s.
  • So, given the frequency of light, its wavelength
    can be calculated, or vice versa.

11
The Wave Nature of Light
  • What is the wavelength of yellow light with a
    frequency of 5.09 x 1014 s-1? (Note s-1,
    commonly referred to as Hertz (Hz) is defined as
    cycles or waves per second.)
  • If c nl, then rearranging, we obtain l c/n

12
The Wave Nature of Light
  • What is the frequency of violet light with a
    wavelength of 408 nm?
  • If c nl, then rearranging, we obtain n c/l.

13
  • What is the wavelength of WONY?
  • What is the wavelength of cell phone radiation?
    Frequency 850 MHz
  • What is the wavelength of a microwave oven?
    Frequency 2.45 GHz

14
Quantization of Energy
Light acts as if it consists of particles called
PHOTONS, with discrete energy.
  • Energy of radiation is proportional to frequency

E h ?
h Plancks constant 6.6262 x 10-34 Js
15
E h ?
Relationships
16
Short wavelength light has
  1. High frequency and low energy
  2. High frequency and high energy
  3. Low frequency and low energy
  4. Low frequency and high energy

17
  • Rank the following in order of increasing photon
    energy
  •  
  • microwaves
  • radiowaves
  • X-rays
  • blue light
  • red light
  • UV light
  • IR light

18
Energy of Radiation
  • What is the frequency of UV light with a
    wavelength of 230 nm?
  • What is the energy of 1 photon of UV light with
    wavelength 230 nm?

19
What is the energy of a photon of 525 nm light?
  1. 3.79 x 10-19 J
  2. 4.83 x 10-22 J
  3. 3.67 x 1020 J
  4. 8.43 x 1023 J

20
Radio Wave Energy
  • What is the energy of a photon corresponding to
    radio waves of frequency 1.255 x 10 6 s-1?

21
  • What is the energy of a mole of 230 nm photons?
  • Can this light break C-C bonds with an energy of
    346 kJ/mol?

22
  • Does 1200 nm light have enough energy to break
    C-C bonds?

23
Where does light come from?
  • Excited solids emit a continuous spectrum of
    light
  • Excited gas-phase atoms emit only specific
    wavelengths of light (lines)

24
Light emitted by solids
25
Light emitted by hydrogen gas
26
The Bohr Model of Hydrogen Atom
  • Light absorbed or emitted is from electrons
    moving between energy levels
  • Only certain energies are observed
  • Therefore, only certain energy levels exist
  • This is the Quanitization of energy levels

27
Emission spectra of gaseous atoms
  • Excited atoms emit light of only certain
    wavelengths
  • The wavelengths of emitted light depend on the
    element.

28
Line spectra of atoms
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Energy Adsorption/Emission
30
  • For H, the energy levels correspond to

Constant 2.18 x 10-18 J
Energy level diagram
31
Each line corresponds to a transition
  • Example n3 ? n 2

32
Explanation of line spectra
Balmer series
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