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Unformatted text preview: Excited Atoms Emit Light! Lithium Sodium Strontium Calcium So what is light? • Electromagnetic radiation, what we refer to as “light”, consists of oscillating electric and magnetic fields. How do we characterize electromagnetic radiation? Light is characterized by its wavelength… • The symbol for wavelength is the Greek letter “lambda” ( λ ). • A wavelength has a unit of length: μ m, mm, cm, m, km. …and by its frequency. • The symbol for frequency is the Greek letter “nu” ( ν ). • Frequency has units of inverse time: s1 . • Frequency is often reported in units of Hertz (Hz), where: s 1 Hz 11 = Relating Wavelength and Frequency • Wavelength and frequency are inversely related via the following equation: • In this equation, “c” is the speed of light. λ c ν = m/s 10 3.00 c 8 × = Relating Wavelength and Frequency • The inverse relationship between wavelength and frequency can be seen below: • The longer the wavelength, the lower the frequency. ↓ ⇒ ↑ ν λ The Electromagnetic Spectrum Increasing λ Increasing ν Radio Waves • AM radio ⇒ A mplitude M odulation – What is a typical wavelength of AM radio waves? • FM radio ⇒ F requency M odulation1 6 6 3 AM s 10 Hz 10 kHz 10 ν = = =1 8 8 2 FM s 10 Hz 10 MHz 10 ν = = = Atoms emit light at discrete wavelengths Sodium Strontium Interactions of Electromagnetic Radiation with Matter • 1900 Max Planck  Blackbody radiation – Solid objects (“blackbodies”) emit light when they are heated. A solid object glows read at 750 ° C and glows white at 1200 ° C. – Examples: Toaster and oven elements, incandescent light bulbs, the sun Blackbody Radiation • What is the temperature of the sun? Wien’s Law • Drawing upon the StefanBoltzmann Law, Wilhelm Wien (1893) determined the following relationship. • Where c 2 = 1.44 x 102 K • m • If λ max for the sun is 490 nm, what is its temperature? 2 max T 5 c λ = 5.88 x 10 K Interactions of Electromagnetic Radiation with Matter • 1900 Max Planck  Blackbody radiation – Planck was able to explain blackbody radiation if he assumed that atoms in a solid oscillated only at certain frequencies, with the energy given by the following expression: .... 4, 3, 2, 1, n nhν E = = Planck’s constant: h = 6.63 x 1034 Js n is a quantum number A Collection of Oscillators The Photoelectric Effect The Photoelectric Effect Interactions of Electromagnetic Radiation with Matter • 1905 Albert Einstein  Photoelectric Effect – Einstein developed a theory for light which could explain the photoelectric effect only if the energy of light came in fixed amounts called photons. – A photon is defined as a particle of electro magnetic energy....
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This note was uploaded on 04/09/2008 for the course CHEM 125 taught by Professor Bussell during the Fall '06 term at Western Washington.
 Fall '06
 Bussell
 Chemistry, Atom

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