## 20170325

### Physics midterm question: Boeing E-6A tail cable antenna reception

Physics 205B Midterm 1, spring semester 2017
Cuesta College, San Luis Obispo, CA

An airplane has a horizontal receiving antenna trailing behind it[*]. It can fly over a transmitting antenna that is aligned horizontally east-west. Discuss whether the airplane will receive more signal while flying over the transmitting antenna in the north-south direction (as shown here), or while flying over the transmitting antenna in the east-west direction, or if there is a tie. Explain your reasoning using the properties of light and polarization.

[*] fas.org/nuke/guide/usa/c3i/e-6.htm.

• p:
Correct. Discusses/demonstrates that signal will be received by the airplane receiving antenna as it flies east-west over the transmitter, and no signal will be received as it flies north-south, because:
1. the east-west transmitter will emit a transverse wave straight upward that has the same east-west polarization as the antenna orientation (also along the north and south directions at ground level);
2. a receiving antenna will best pick up a transverse radio wave when its orientation matches the polarization of the radio wave, and pick up no signal when its orientation is perpendicular to the polarization of the radio wave.
• r:
As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. May have a "T" at the end of the cable trailing the aircraft, such that its receiving orientation is parallel to its wings instead of parallel to its fuselage.
• t:
Nearly correct, but argument has conceptual errors, or is incomplete. Typically only explanation for (1) is complete, but not (2).
• 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: midterm01AhC4
p: 16 students
r: 3 students
t: 5 students
v: 5 students
x: 1 student
y: 0 students
z: 0 student

A sample "p" response (from student 6969):