Astronomy quiz question: same size, but different temperature stars

Astronomy 210 Quiz 4, fall semester 2011
Cuesta College, San Luis Obispo, CA

[Version 1]
A(n) __________ has the same size as, but is cooler than a G0 supergiant.
(A) A5 supergiant.
(B) B0 main sequence star.
(C) M5 giant.
(D) G0 white dwarf.

Correct answer: (C).

Using an H-R diagram, the G0 white dwarf is much smaller than the G0 supergiant, and is the same temperature. The B0 main sequence star the same luminosity as the G0 supergiant, and is hotter than the G0 supergiant. The only stars that have the same size as a G0 supergiant are an A5 supergiant and an M5 giant. However, the A5 supergiant is hotter than the G0 supergiant, while the M5 giant is cooler than the G0 supergiant.

Section 70158
Exam code: quiz04sIZ3
(A) : 2 students
(B) : 8 students
(C) : 22 students
(D) : 5 students

Success level: 63% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.28

[Version 2]
A(n) __________ has the same size as, but is hotter than a G0 supergiant.
(A) A5 supergiant.
(B) B0 main sequence star.
(C) M5 giant.
(D) G0 white dwarf.

Correct answer: (A).

Using an H-R diagram, the G0 white dwarf is much smaller than the G0 supergiant, and is the same temperature. The B0 main sequence star the same luminosity as the G0 supergiant, and is hotter than the G0 supergiant. The only stars that have the same size as a G0 supergiant are an A5 supergiant and an M5 giant. However, the M5 giant is cooler than the G0 supergiant, while the A5 supergiant is hotter than the G0 supergiant.

Section 70160
Exam code: quiz04nuO6
(A) : 13 students
(B) : 5 students
(C) : 3 students
(D) : 3 students

Success level: 58% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.83