METR 104:
Our Dynamic Weather

(Lecture w/Lab)
Pre-class Quiz #6:
for on-Line Reading #6
Dr. Dave Dempsey
Dept. of Geosciences
SFSU, Fall 2012

This is a "preview" version of Pre-class Quiz #6, which is based on on-line Reading Assignment #6. The "preview" version is suitable for printing and leisurely inspection before you submit your answers to the the interactive or "live" version—that is, the real thing. When you feel ready to submit your answers, go to iLearn's METR 104 "Pre-class Quizzes" section, select the interactive version, and follow its instructions.

Responses must be submitted by 1:05 p.m. Wednesday, Nov. 28. (If you leave the interactive version before submitting your answers, you can save answers already entered by clicking on the "Save without submitting" button at the bottom of the quiz page, and you can return later. In any case, be sure to submit your responses by the deadline by clicking on the "Submit all and finish" button at the bottom of the quiz page.)

You will have two chances to get each question correct. (If you want to resubmit your answers, you will have to wait at least 10 minutes after the first submission.)

Description: The nine questions below (all are multiple choice) address points made about water vapor and clouds in On-line Reading Assignment #6.

The Questions:


(1) Multiple Choice. Changes of State or Phase of Water. Which of the following changes of state or phase of water adds water vapor to the air? (Select the one correct answer.)

  1. condensation and melting
  2. evaporation and sublimation
  3. freezing and deposition

(2) Multiple Choice. The Capacity of Air to Hold Water Vapor. There is an upper limit to the amount of water vapor that can be present in the air. When that limit is reached, we say that the air is saturated with water vapor because the air can't "hold" any more.

What determines the upper limit to, or the maximum amount of , water vapor that air can "hold"? (Choose the one [best] correct answer.)

  1. The amount of water vapor actually present in the air.
  2. The temperature of the air.
  3. The air pressure.
  4. The dew point temperature.

(3) Multiple Choice. Relative Humidity. Humidity is a broad term referring to the amount of water vapor in the air. One particular, more specific measure of humidity is relative humidity. How is relative humidity defined? (Choose the one correct answer.)

  1. The amount of water vapor in the air.
  2. The amount of water vapor in the air relative to (that is, expressed as a fraction or percentage of) the amount of other gases in the air.
  3. The amount of water vapor in the air relative to (that is, expressed as a fraction or percentage of) the amount of water vapor needed to saturate the air.
  4. The amount of water vapor in the air relative to (that is, expressed as a fraction or percentage of) the dew point temperature.

(4) Multiple Choice. Relative Humidity: Dependence on Temperature. What happens to the relative humidity when air warms up (for example, inside a heated house or apartment on a cold winter day)?

(Assume that the actual amount of water vapor present in the air does not change by, say, evaporation of liquid water into it.) (Choose the one correct answer.)

  1. The relative humidity goes up.
  2. The relative humdity doesn't change.
  3. The relative humidity goes down.

(5) Multiple Choice: Dew Point Temperature. Humidity is a broad term referring to the amount of water vapor in the air. One particular, more specific measure of humidity is dew-point temperature, which is defined as the temperature to which air must be cooled to saturate it.

What determines the dew-point temperature of a "parcel" (small blob) of air? (Choose the one [best] correct answer.)

  1. The parcel's temperature.
  2. The parcel's pressure.
  3. The water vapor content of the parcel.
  4. The parcel's direction and speed of motion.

(6) Multiple Choice. Pressure Variation with Increasing Altitude. As you (or a rising "parcel" of air) go higher in the atmosphere, what happens to the atmospheric pressure on you (or the parcel)? (Choose the one correct answer.)

  1. The pressure increases.
  2. The pressure decreases.
  3. The pressure doesn't change.
  4. The pressure decreases at first, then stops changing for a while in the lower stratosphere, then increases with increasing altitude in the stratosphere.

(7) Multiple Choice. Adiabatic Temperature Changes. What happens to the temperature of an air "parcel" when the pressure on the parcel decreases and (as a result) the parcel expands? (Choose the one correct answer.)

  1. The parcel warms.
  2. The parcel cools.
  3. The parcel's temperature doesn't change.

(8) Multiple Choice. Cloud Formation. What must happen for a cloud to form in the atmosphere? (Choose the one correct answer.)

  1. Air must gain more water vapor by evaporation.
  2. Air must warm sufficiently.
  3. Air must cool below its dew point temperature.
  4. The dew point temperature must rise sufficiently.

(9) Multiple Choice. Clouds along Fronts. Why do clouds tend to form along fronts? (Choose the one best answer.)

  1. Air is forced to rise along fronts, and it cools adiabatically enough for clouds to form.
  2. Cold fronts are areas of large cold air advection.
  3. Fronts are places where a lot of evaporation occurs.
  4. Fronts are often places with very active weather.

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