20120210

Physics quiz question: reception from electric dipole antenna

Physics 205B Quiz 1, spring semester 2012
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Multiple-Choice Question 22.1

"KJ4AED And His Portable 40m Antenna"
Greg Cohoon
flic.kr/p/6PMS1H

A radio station is located due south of your location. It uses an electric dipole antenna oriented horizontally north-south. In order to maximize reception of this broadcast at your location, you need to orient an electric dipole receiving antenna:
(A) vertically.
(B) horizontally north-south.
(C) horizontally east-west.
(D) (No reception is possible using an electric dipole antenna.)

Correct answer (highlight to unhide): (D)

An electric dipole antenna will broadcast most effectively in all directions perpendicular to its orientation, which for this horizontal north-south antenna would be to the east and to the west of its location (as well as directly overhead, or anywhere in the sky along an east-to-west line). There would be zero signal broadcast to the north and to the south of the antenna, as those locations would be looking at the antenna end-on, and there would be no detectable transverse oscillations.

Section 30882
Exam code: quiz01pL2r
(A) : 2 students
(B) : 2 students
(C) : 4 students
(D) : 21 students

Success level: 72%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.83

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