## 20160327

### Physics midterm question: reception from an electric dipole antenna

Physics 205B Midterm 1, spring semester 2016
Cuesta College, San Luis Obispo, CA

A radio transmitter broadcasts using a horizontal electric dipole antenna mounted along the north-south direction. A Physics 205B student holding a vertical receiver is located to the west of the transmitter, and walks to the south of the transmitter. Discuss whether the signal (if any) received by the Physics 205B student will increase, decrease, or not change as she walks from west to south. Explain your reasoning using the properties of light and polarization.

• p:
Correct. Discusses/demonstrates that no signal will be received by the Physics 205B student's vertical receiving antenna as she walks from west of to the south of the horizontal north-south transmitting antenna because:
1. her vertical antenna cannot receive a horizontally polarized radio signal emitted by the transmitting antenna to the west, and;
2. the transmitting antenna does not broadcast any signal to the south, along its antenna axis.
• r:
As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. Typically only explanation for (1) is complete, but not (2).
• t:
Nearly correct, but argument has conceptual errors, or is incomplete. Typically only explanation for (2) is complete, but not (1).
• v:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some garbled attempt at applying the properties of light (radio waves) and polarization.
• x:
Implementation/application of ideas, but credit given for effort rather than merit. No clear attempt at applying the properties of light (radio waves) and polarization.
• y:
Irrelevant discussion/effectively blank.
• z:
Blank.
Sections 30882, 30883
Exam code: midterm01rx1C
p: 25 students
r: 8 students
t: 8 students
v: 2 students
x: 0 students
y: 0 students
z: 0 student

A sample "p" response (from student 2468):

A sample "t" response (from student 0558):