Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problems 18.21, 18.31
[10 points.] An ideal emf source is connected in series to two light bulbs, one of which is much brighter than the other. Which light bulb has the greater resistance? Explain your reasoning using the properties of currents and potential differences, and Kirchhoff's rules and Ohm's law. Solution and grading rubric:
- p = 10/10:
Correct. Uses Ohm's law and power relations (P = I*delta(V) and/or I^2/R), along with recognizing that the same amount of current must pass through both these light bulbs in series to conclude that the bright light bulb has the greater resistance. - 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. - t = 6/10:
Nearly correct, but argument has conceptual errors, or is incomplete. - 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: 6 students
r: 2 students
t: 3 students
v: 2 students
x: 0 students
y: 0 students
z: 0 students
A sample "p" response (from student 6886):
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