Physics Pre-Instruction Quiz

Radiative Transfer

 
About Pre-Quizzes

Note to the student:  The following pre-quiz will not affect your grade.  It is for informational purposes only.

1. Why do we have seasons? For example, why is it colder in winter than in summer? Give a brief explanation.
 
 
 

2. You hold your hands near a light bulb, as shown. One hand is above, one hand is to the side, but both hands are the same distance from the bulb. The light bulb is switched on, and your hands feel heat. Which hand feels heat first?

                              

Give a brief explanation of your answer:
 

Results of this Pre-Quiz on Radiation

Question 1:   In a sample of 21 physics students, 3 or 4 of them invoked variations in the distance to the sun as the cause behind the seasons, and even the differences between the poles and equator.  Many more students replied that "the earth's tilt" accounted for the seasons, or drew a fairly accurate sketch of a tilted earth in orbit, but were unable to actually explain the process by which more solar energy was intercepted by a square meter of surface at one location than another, or one time of year than another.

Question 2:   In the light bulb question, about half the students thought the top hand would feel the heat first.  This was a more pervasive misconception than the seasons, probably because many had some formal instruction on seasons, and many have informal experience with candles, in which convective heat transfer is important.  In the first moments after the bulb is switched on, the only heat energy comes from radiation, and the two hands feel this instantly.
 

Implications for Teaching about Earth's Radiation Budget:

It is important that students go through exercises that enable them to understand how the differing altitude of the sun in the sky accounts for seasons, before trying to link the heating variations to sea level changes.  Likewise, students need to understand the essentials of radiative heat transfer (no medium is needed, and it travels fast) before trying to make extensions to earth processes.

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