Planck's Equation for Blackbody Radiation
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Questions and Answers

What is used to express the time of day in solar energy calculations?

  • Mean Solar Time (MST)
  • Apparent Solar Time (AST) (correct)
  • Local Standard Time (LST)
  • Daylight Saving Time (DST)

    • What is the time when the sun crosses the meridian of the observer called?

  • Equation of Time (ET)
  • Longitude Correction Time
  • Mean Solar Noon
  • Local Solar Noon (correct)

    • What factor causes the Equation of Time (ET) variation throughout the year?

  • Earth's inner core temperature
  • Earth's orbital eccentricity (correct)
  • Earth's tilt angle
  • Earth's rotation speed

    • Why does Apparent Solar Time (AST) differ slightly from mean time kept by a clock?

    <p>Because of Earth's orbital velocity variations</p> Signup and view all the answers

    What must be used to convert Local Standard Time (LST) to Apparent Solar Time (AST)?

    <p>Longitude correction</p> Signup and view all the answers

    Which factor contributes to the non-uniform length of a day throughout the year?

    <p>Earth's axial tilt</p> Signup and view all the answers

    What is the significance of the plus sign in Eq (2.4) when calculating the sun-earth distance?

    <p>Indicates the sun-earth distance at aphelion position</p> Signup and view all the answers

    How is the mean sun-earth distance, 'a', defined?

    <p>Half the sum of perihelion and aphelion distances</p> Signup and view all the answers

    What is the approximate percentage difference between the longest and shortest sun-earth distances?

    <p>3.3%</p> Signup and view all the answers

    In which season is the sun higher in the sky according to common knowledge?

    <p>Summer</p> Signup and view all the answers

    How often does the earth move around the sun in an elliptical orbit?

    <p>Yearly</p> Signup and view all the answers

    What does the equation R = a(1 - e) represent?

    <p>Sun-earth distance at perihelion</p> Signup and view all the answers

    What is the name of the equation derived by Max Planck to describe the monochromatic emissive power of a blackbody?

    <p>Planck's equation for blackbody radiation</p> Signup and view all the answers

    What does the constant C1 represent in Planck's equation for blackbody radiation?

    <p>Constant related to radiation intensity</p> Signup and view all the answers

    How is the equation (2.34) modified when the surface is not in a vacuum or a gas?

    <p>By replacing C1 with C1/n^2</p> Signup and view all the answers

    What type of surfaces are often considered as diffuse reflectors in engineering calculations?

    <p>Rough surfaces</p> Signup and view all the answers

    What does Wien's displacement law provide?

    <p>The wavelength corresponding to the maximum of the distribution for blackbody radiation</p> Signup and view all the answers

    A real surface is both a diffuse emitter and a diffuse reflector. What does this imply about the radiosity of the surface?

    <p>It remains constant in all directions</p> Signup and view all the answers

    Which constant is used to calculate C2 in Planck's equation for blackbody radiation?

    <p>Boltzmann’s constant</p> Signup and view all the answers

    What is the equation used for a real surface to calculate the intensity of radiation from it?

    <p>$J = 2.43 \times I$</p> Signup and view all the answers

    What does C2 represent in Planck's equation for blackbody radiation?

    <p>Constant related to temperature</p> Signup and view all the answers

    In Example 2.10, what is the transmissivity of the glass used in the application for wavelengths 0.3 and 3.0 mm?

    <p>0.92</p> Signup and view all the answers

    What percentage of incident solar energy is transmitted through the glass for wavelengths between 0.3 and 3.0 mm?

    <p>94.61%</p> Signup and view all the answers

    Based on the provided text, what is the primary assumption made about the interior of the application mentioned in Example 2.10?

    <p>It is a blackbody at 373 K</p> Signup and view all the answers

    What is the total emissive power of the surface when the average emissive power over the entire wavelength is given as 0.4432?

    <p>25129.4 W/m2</p> Signup and view all the answers

    At a temperature of 2500 K, what is the computed value of Eb for the given surface?

    <p>0.63371 sT^4</p> Signup and view all the answers

    What is the average absorptivity of the surface when the spectral absorptivity values are 0.2 and 0.7 for different wavelengths?

    <p>0.383</p> Signup and view all the answers

    Based on the Kirchhoff's law, if a(T) = 0.383, what is the reflectivity (r) of the surface?

    <p>0.617</p> Signup and view all the answers

    At a temperature of 2500 K, what is the computed value of ε(T) based on Eq.(2.41) and the provided average absorptivity value?

    <p>0.383</p> Signup and view all the answers

    What law is used to obtain other properties of materials as demonstrated in Example 2.12?

    <p>Kirchhoff’s law Eq.(2.40)</p> Signup and view all the answers

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