Cuesta College, San Luis Obispo, CA
An astronomy question on an online discussion board[*] was asked and answered:
??: Because the moon is already bright, is it not necessary to get a telescope with a wide diameter to be able to see small details on the moon?Discuss why this response is incorrect. Support your answer using the properties of telescopes and telescope powers.
Clv: Yes, so what you want is more magnification, and for that you need a lens or mirror with a longer focal length.
[*] answers.yahoo.com/question/index?qid=20150925202048AAO1s8p
Solution and grading rubric:
- p:
Correct. Discusses how focal length of a telescope's primary mirror or lens (along with the focal length of the eyepiece) determines the magnification, but is only important of "small details" are already able to be seen due to the resolving power of the telescope, which depends on the diameter of the primary mirror/lens. Also discusses how light-gathering power depends on the area of the primary mirror/lens (which by itself is less important due to the brightness of the moon). - r:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Correct and complete discussion of two of the three telescope parameters and powers. - t:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. Problems with either diagram or discussion. Discussion of only one of the three telescope parameters and powers is correct and complete. - v:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. - x:
Implementation/application of ideas, but credit given for effort rather than merit. Misconceptions or non-relevant concepts. - y:
Irrelevant discussion/effectively blank. - z:
Blank.
Section 70158
Exam code: midterm01sF1A
p: 22 students
r: 15 students
t: 3 students
v: 1 student
x: 0 students
y: 0 students
z: 1 student
A sample "p" response (from student 4338):
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