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Chapter 6: Electromagnetic Radiation
wavelength Visible light Ultraviolet radiation Amplitude Node
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Figure 7.1
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Short wavelength -->
high frequency high energy Long wavelength --> small frequency low energy
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Which has the longest wavelength?
Infrared Ultraviolet X-rays Radio waves
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Rank the following in order of increasing frequency: microwaves radiowaves X-rays blue light red light UV light IR light
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Long wavelength --> small frequency
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
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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
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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 = Planck’s constant = x J•s
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E = h • Relationships:
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Short wavelength light has:
High frequency and low energy High frequency and high energy Low frequency and low energy Low frequency and high energy
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Rank the following in order of increasing photon energy: microwaves radiowaves X-rays blue light red light UV light IR light
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E = h • n What is the energy of a WONY photon?
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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?
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What is the energy of a photon of 525 nm light?
3.79 x J 4.83 x J 3.67 x 1020 J 8.43 x 1023 J
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Can this light break C-C bonds with an energy of 346 kJ/mol?
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?
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Does 1200 nm light have enough energy to break C-C bonds?
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Where does light come from?
Excited solids emit a continuous spectrum of light Excited gas-phase atoms emit only specific wavelengths of light (“lines”)
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Light emitted by solids
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Light emitted by hydrogen gas
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