Cuesta College, San Luis Obispo, CA
A red supergiant can have the same luminosity as a white main-sequence star if the red supergiant is:
(A) cooler and smaller.
(B) cooler and larger.
(C) hotter and smaller.
(D) hotter and larger.
Correct answer (highlight to unhide): (B)
From Wien's law, the red supergiant is cooler than the white main-sequence star. In order to have the same luminosity, from the Stefan-Boltzmann law, the red supergiant must be larger in size to compensate for its lower temperature, compared to the white main-sequence star, which must be smaller in size to compensate for its higher temperature.
The entries for the "box method" of comparing relative Stefan-Boltzmann parameters are listed below.
| Lum. | = | size | × | Temp.4 | |
| Red s.g. | = | ↑ | ↓ | ||
| White m.s. | = | ↓ | ↑ |
Section 70158
Exam code: quiz05GieH
(A) : 6 students
(B) : 23 students
(C) : 13 students
(D) : 5 students
Success level: 52% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.64
Section 70160
Exam code: quiz05Nuhl
(A) : 4 students
(B) : 14 students
(C) : 7 students
(D) : 2 students
Success level: 56% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 1.00
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