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Blackbody Radiation

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Blackbody Radiation Answer Key

Instructions: Read each question carefully. Choose the answer that best fits the question. Short answer response questions must be responded to in complete sentences. If the question involves calculations, you must show all your math work.

Planck's law relates to the radiation that which of the following emits in thermal equilibrium at a specific temperature?
  1. ideal gas
  2. infinite light source
  3. black body
What is a blackbody?
  • A blackbody an idealized physical body that absorbs all incident electromagnetic radiation and re-emits it, such as a star.
The total energy radiated per unit surface area of a black body across all wavelengths per unit time is called                    .
  1. irradiance
  2. radiant exitance
  3. flux intensity
  4. black body spectrum
According to the Stefan-Boltzmann Law, the radiant exitance or emissive power is directly proportional to the fourth power of the black body's                          .
  1. kinetic energy
  2. mass
  3. thermodynamic temperature
  4. specific heat
Explain blackbody radiation.
  • Blackbody radiation refers to the electromagnetic radiation emitted by an object or system which absorbs all radiation incident upon it, and then, re-radiates that energy. Blackbody radiation is determined by the temperature alone.
For “grey body” radiation represented by the equation, [math]j^"*"=epsilon sigma T^4[/math], what is the value of emissivity, [math]epsilon [/math]?
  1. less than one
  2. equal to one
  3. greater than one
Explain the significance of the Rayleigh-Jeans Law.
  • Although found to be an inaccurate description of nature, the Rayleigh-Jeans Law was an important step in our understanding of the equilibrium radiation emitted by a hot object because an experimental comparison of the Rayleigh-Jeans Law and the quantum Planck radiation formula confirmed the relationship in Planck’s constant.
Explain Wein’s Displacement Law.
  • Wien's displacement law states that the wavelength of the peak of a blackbody’s radiation curve gives a measure of that blackbody’s temperature.
How do modern physicists use Wein's Displacement Law?
  • Wein’s Displacement Law is useful for the determining the temperatures of any radiant object whose temperature is far above that of its surroundings, such as the temperature of distant stars.

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