20100602

Physics final exam question: virtual image from converging lens

Physics 205B Final Exam, Spring Semester 2010
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Multiple-Choice Question 23.7

[10 points.] An object is placed to the left of a converging lens, producing a virtual image. Determine whether this image is upright or inverted, and whether this image is enlarged or diminished. Explain your answer using equations and/or diagrams.

Solution and grading rubric:
  • p = 10/10:
    Correct. Explains how a converging lens will always create an upright, enlarged virtual image of an object placed to the left it using equations and/or ray tracing diagrams.
  • r = 8/10:
    As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. Discussion based on recollection of facts, but with no explicit equations or diagrams.
  • t = 6/10:
    Nearly correct, but argument has conceptual errors, or is incomplete. Discussion of a real image using equations and/or ray tracing diagrams.
  • v = 4/10:
    Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner.
  • x = 2/10:
    Implementation/application of ideas, but credit given for effort rather than merit.
  • y = 1/10:
    Irrelevant discussion/effectively blank.
  • z = 0/10:
    Blank.

Grading distribution:
Section 31988
p: 4 students
r: 2 students
t: 3 students
v: 3 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 1930):

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