Astronomy quiz question: same luminosity giant and main sequence star

Astronomy 210 Quiz 4, Spring Semester 2011
Cuesta College, San Luis Obispo, CA

A giant star has the same luminosity as a main sequence star. As the giant is larger, it will have a __________ than the main sequence star.
(A) cooler temperature.
(B) hotter temperature.
(C) smaller parallax angle.
(D) larger parallax angle.

Correct answer: (A)

The Stefan-Boltzmann law states that luminosity is proportional to size (that is, surface area) and temperature (T^4). Since these two stars have the same luminousity, then the larger star must be cooler than the smaller star.

Section 30674
(A) : 29 students
(B) : 4 students
(C) : 2 students
(D) : 4 students

"Success level": 78% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.60
Exam code: quiz04nK4n