CHAPTER 6

CHAPTER 6 - WavesofLight ElectromagneticRadiation...

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Waves of Light Electromagnetic Radiation Not all radiation is equal Prisms break sunlight into spectrum of colors Colors identified by numerical value (wavelength) 
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Electromagnetic Radiation
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Electromagnetic Radiation Wave traveling  through space Electric field Magnetic field
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Electromagnetic Radiation Wavelength (Greek lambda,  λ ) distance between corresponding points on adjacent waves Expressed in units of length:  nanometers (nm)
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Wave Nature of Light
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Relation between  υ  and  λ   As  υ  (frequency) increases λ  (wavelength) decreases As  υ   decreases λ  increases Frequency =  υ  = c/ λ c= speed of light   3.00 x 10 8  meters/second  or 186,000 miles/second λ   and  υ  are inversely related
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Fig. 2.6 Electromagnetic Spectrum
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Electromagnetic Radiation
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Electromagnetic Radiation The red light in a laser pointer comes from a diode laser  that has a wavelength of about 630 nm. What is the  frequency of the light? c  = 3.00 x 10 8  m/s –1
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Light as a Particle In the early 20th century, several  discoveries led to a particle model of light. Photons: “particles” of light Energy of a photon: E = h  ν h = “Planck’s Constant”= 6.626 x 10 –34  J s
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Planck’s Equation Energy, E = h  υ  = hc /  λ E is the energy of a single photon c = 3.00 x 10 8  m/sec h, Planck’s constant = 6.63 x 10 -34  joule sec Joule is a unit of energy Energy is directly proportional to  υ  (frequency)  and inversely  proportional to  λ  (wavelength) As      , E  As      , E 
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Electromagnetic Spectrum Energy (J)
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The Energy and Frequency of Quanta Radiation λ ν E Photon E mol (m) (s -1 ) (J) (kJ/mol) Radio Wave 10 3.0x 10 7 2.0 x 10 -26 1.2x10 -5 -22 30 -3 21
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Photon Energy A laser emits red light with wavelength of 630 nm (1 nm = 10 –9  m) What is the energy of a photon at this Wavelength?
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Photoelectric Effect Particulate Nature of Light Shine light on metal  (cathode) Electrons emitted Detect number of  electrons and kinetic  energies  Current flow used to  monitor light  intensity.
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Photoelectric Effect
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Photoelectric Effect Binding Energy - energy holding an  electron to a metal. Threshold frequency,  ν o  - minimum frequency  of light needed to emit an electron. For frequencies below the threshold frequency,  no electrons are emitted. For frequencies above the threshold 
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CHAPTER 6 - WavesofLight ElectromagneticRadiation...

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