Cuesta College, San Luis Obispo, CA
Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 25.1
A radio antenna receives a destructive interference signal from two transmitters that broadcast in phase at the same wavelength. Discuss why the radio antenna will still receive a destructive interference signal if both of the two transmitters are each moved one-half of a wavelength farther away from their current distances from the radio antenna. Explain your reasoning by using the properties of waves and interference.
Solution and grading rubric:
Correct. Recognizes that (a) the two waves from in phase sources interfere destructively, so the path length difference ∆l = (m + 1/2)∙λ, and (b) demonstrates by either drawings or explicit math how extending both paths by half a wavelength will not affect the path length difference, thus the interference will still be destructive as stated.
As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. Typically recognizes that ∆l will not be affected by moving both transmitters by half a wavelength, but does not explicitly demonstrate how this is so.
Nearly correct, but argument has conceptual errors, or is incomplete.
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner.
Implementation/application of ideas, but credit given for effort rather than merit.
Irrelevant discussion/effectively blank.
Sections 30882, 30883
Exam code: midterm01b0w7
p: 14 students
r: 14 students
t: 11 students
v: 1 student
x: 1 student
y: 0 students
z: 0 students
A sample "p" response (from student 5297):
Another sample "p" response (from student 3420):