Chem 125 - 2 - Chapter 12

Chem 125 - 2 - Chapter 12 - Excited Atoms Emit Light!...

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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 ( ). A wavelength has a unit of length: m, mm, cm, m, km. and by its frequency. The symbol for frequency is the Greek letter nu ( ). Frequency has units of inverse time: s-1 . Frequency is often reported in units of Hertz (Hz), where: s 1 Hz 1-1 = Relating Wavelength and Frequency Wavelength and frequency are inversely related via the following equation: In this equation, c is the speed of light. c = 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. The Electromagnetic Spectrum Increasing Increasing Radio Waves AM radio A mplitude M odulation What is a typical wavelength of AM radio waves? FM radio F requency M odulation-1 6 6 3 AM s 10 Hz 10 kHz 10 = = =-1 8 8 2 FM s 10 Hz 10 MHz 10 = = = 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? Wiens Law Drawing upon the Stefan-Boltzmann Law, Wilhelm Wien (1893) determined the following relationship. Where c 2 = 1.44 x 10-2 K m If max for the sun is 490 nm, what is its temperature? 2 max T 5 c = 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 nh E = = Plancks constant: h = 6.63 x 10-34 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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Chem 125 - 2 - Chapter 12 - Excited Atoms Emit Light!...

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