Cuesta College, San Luis Obispo, CA
An astronomy question on an online discussion board[*] was asked and answered:
Pdg: Your friend asks, "Of all the stars we can see in the sky tonight, which is the largest one?" You search all over the sky--should you point to a star that is bright and red, or dim and orange? (Assuming they are equally far away.)Discuss why this answer is correct, and how you know this. Explain using Wien's law, the Stefan-Boltzmann law and/or an H-R diagram.
Thms: Bright and red.
[*] answers.yahoo.com/question/index?qid=20130919144534AAHf3r4.
Solution and grading rubric:
- p:
Correct. Uses Wien's law, the Stefan-Boltzmann law and/or interprets H-R diagram to show specifically how the "bright and red" star is cooler and more luminous, and thus must be larger in size than the "dim and orange" star, which is hotter and less luminous. - r:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. - t: Contains right ideas, but discussion is unclear/incomplete or contains major errors.
- v:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least attempts to use Wien's law, H-R diagram and/or the Stefan-Boltzman law. - x:
Implementation/application of ideas, but credit given for effort rather than merit. Discussion not based on Wien's law, H-R diagram and/or the Stefan-Boltzman law. - y:
Irrelevant discussion/effectively blank. - z:
Blank.
Section 70158
Exam code: midterm02sL4g
p: 19 students
r: 8 students
t: 13 students
v: 7 students
x: 1 student
y: 0 students
z: 0 students
A sample "p" response (from student 6933) using an H-R diagram (provided on the exam):
Another sample "p" response (from student 0483) using a "box-method" analysis of the Stefan-Boltzmann law:
Yet another sample "p" response (from student 2729), using both an H-R diagram and a Stefan-Boltzmann law "box":
A sample "x" response (from student 0126):
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