ERTH 535:
Planetary Climate Change
(Spring 2018)
Pre-class Quiz #1:
Laws of Radiation
Dr. Dave Dempsey
Dept. of Earth & Climate Sci.,
SFSU

This is a "preview" version of Pre-class Quiz #1. The preview version is suitable for printing and leisurely inspection before you submit your answers to the interactive or "live" version—that is, the real thing. When you feel ready to submit your answers, go to iLearn's ERTH 535 "Pre-class Quiz" section, select the interactive version, and follow its instructions.

(Responses must be submitted via iLearn by 12:00 p.m. on Friday, Feb. 9.

Note: the candidate answers to each question below might not appear in the same order on iLearn as they do here, so be careful when transferring answers from this preview version to iLearn.)

Description: The questions below are based on Reading Assignment #2. They address aspects of radiation relevant to understanding the earth's planetary energy budget.

Questions:


(1) Multiple Choice. The inverse-square law describes how the radiative energy flux (that is, the radiative energy intensity) from a "point" source of radiation, such as a light bulb, the sun, or the earth, varies with distance from the source. What does this law say? (Pick the one best answer.)

  1. The radiative energy flux from a "point" source decreases steadily with distance from the source.
  2. The radiative energy flux from a "point" source is conserved once the radiation leaves the source.
  3. The radiative energy flux from a "point" source decreases with (in particular, is inversely proportional to) the square of the distance from the source.
  4. The radiative energy flux from a "point" source increases linearly with (i.e., is proportional to) distance from the source.

(2) Multiple Answer. What factor(s) affect the insolation measured on a horizontal surface at the top of the earth's atmosphere at a particular place and time? (Choose all correct answers—there might be more than one.)

  1. the latitude of the place
  2. the time of year
  3. the time of day
  4. the distance between the earth and the sun
  5. the rate at which the sun emits radiative energy

(3) Multiple Choice. What is the solar constant? (Pick the one correct answer.)

  1. The rate at which the sun produces radiative energy.
  2. The idea that the radiative output of the sun is roughly constant over time.
  3. The rate at which solar radiative energy passes through a unit of horizontal area at the "top" of the earth's atmosphere at the earth's mean distance from the sun.
  4. The rate at which solar radiative energy passes through a unit of area directly facing the sun at the "top" of the earth's atmosphere at the earth's mean distance from the sun.

(4) Multiple Choice. How is albedo, the reflectivity of an object (including, for example, the earth as a whole), defined? (Pick the one correct answer.)

  1. The fraction (or percentage) of radiative energy striking a surface that the surface reflects.
  2. The fraction (or percentage) of radiative energy striking a surface that the surface absorbs.
  3. The fraction (or percentage) of radiative energy striking a surface that passes through the surface unaffected.
  4. The fraction (or percentage) of radiative energy coming from a surface that the surface itself emits.

(5) Multiple Choice. The Stefan-Boltzmann Law is one of the basic laws of radiation. What does it say? (Pick the one correct answer.)

  1. The single wavelength of radiation that a blackbody emits the most intensely is inversely proportional to the blackbody's absolute temperature.
  2. The flux of radiative energy emitted by a blackbody (and most other objects) is proportional to the blackbody's absolute temperature.
  3. The flux of radiative energy emitted by a blackbody (and most other objects) is proportional to the blackbody's absolute temperature raised to the fourth power.
  4. Blackbodies (and most other objects) emit some wavelengths of radiative energy more intensely than others.
  5. The flux of radiative energy emitted by a "point source" (e.g., a light bulb, the sun, or the earth, sort of) is inversely proportional to the square of the distance from the source.

(6) Multiple Choice. How is the effective radiating temperature of a planet defined? (Pick the one best answer.)

  1. The single temperature that the planet would have to have to emit radiative energy to space at the same total rate as the entire planet is observed to radiate.
  2. The temperature that a true blackbody would have to have to emit radiative energy to space with the same average intensity as the planet is observed to radiate.
  3. The minimum temperature that the planet must have to emit radiative energy effectively.
  4. The global average temperature of the planet.

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