Ch12 notes part 1 - CH301 Chapter 1 Notes: Part 1:....

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CH301 Chapter 1 Notes: Part 1:. Electromagnetic Radiation . A form of energy our eyes only detect a tiny portions of; various modern detectors ‘see’ a much wider range. Isaac Newton sent white light through a prism - noted its a mix of many different colors. Light behaves in many experiments as if it were a wave . Waves have known properties. Properties of Waves - specifically Light Waves have three linked components: Specifically for electromagnetic waves : Wavelength λ, speed c frequency ν For electromagnetic radiation, c = ν λ c = speed of light = 3 x 10 8 m/s What is ‘waving’? (Fig 12.1) The strength ( amplitude) of both Electrical and Magnetic Fields varies: There are two waves, one at right angles to the other, both traveling in the same direction. The Electromagnetic Spectrum (Fig 12.3) “Light” is just a tiny section of the entire E-M spectrum. Extends in both directions. Example: What is the frequency of green light, wavelength 520 nm? The Electromagnetic Spectrum: what you need to know: (Fig 12.2, 12.3) In addition to being able to use c = νλ , you should be able to determine for different given types of electromagnetic radiation: Which has the longer (bigger) wavelength? Which has the shorter (smaller) wavelength? Which has the highest (greatest, largest) frequency? Which has the lowest (smallest) frequency? Know the Visible range: 400nm-700nm (0.4-0.7 μ m) Know the names of the others (not the wavelength ranges) Know the order: (inc. wavelength) : Gamma rays, X rays, UV, Visible, IR, Microwave, Radio Know the short wavelength (higher frequency) end of the visible is BLUER Know the long wavelength (lower frequency) end of the visible is REDDER Blackbody Radiation (Fig 12.4) All objects above absolute zero emit some E-M radiation. ‘Blackbody’ - an object that can absorb or emit any wavelength of light with equal efficiency. Blackbodies emit radiation over all wavelengths but the relative amounts of each wavelength will vary depending on the temperature. At room temperature very little radiation is emitted at very high or low wavelengths, most will be emitted in the infrared. What happens to the coil on your electric stove, or a light bulb wire as you turn on the power.? Hot objects appear to glow (incandescence). As temperature increases: we sense more heat (IR) coming from the object. The object glows dull red, then orange, then yellow, then white. The distribution is a series of lopsided curves of emitted energy intensity vs. wavelength. For each temperature, there is a peak. How does the peak and the distribution change as T increases? How does the area under the peak change as T increases?
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Blackbody Radiation and the UV Catastrophe Theoreticians could NOT reproduce this experimental data. The classical mechanics model worked poorly at long wavelengths AND predicted infinite values at short wavelengths! “The ultraviolet catastrophe” : Any body above absolute zero would be emitting
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Ch12 notes part 1 - CH301 Chapter 1 Notes: Part 1:....

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