Astronomy quiz question: changing apparent and absolute magnitudes

Astronomy 210 Quiz 4, spring semester 2013
Cuesta College, San Luis Obispo, CA

[Version 1] Mirfak is a star that has an apparent magnitude of m = +1.8, and an absolute magnitude M_V of –5.1. If Mirfak were moved to 10 parsecs away from Earth, its __________ would get dimmer.
(A) apparent magnitude m.
(B) absolute magnitude M_V.
(C) (Both of the above choices.)
(D) (None of the above choices.)

Correct answer: (D)

Mirfak appears to be +1.8 as seen from its true distance from Earth, but when placed at the "fair" distance of 10 parsecs away, it becomes much brighter (−5.1). Thus Mirfak was brought much closer to Earth when moved to 10 parsecs, and was located much farther than 10 parsecs away from Earth. When moved to 10 parsecs away from Earth, its apparent magnitude m would get brighter, while its absolute magnitude M_V would remain the same.

Section 30674
Exam code: quiz04Ni7E
(A) : 17 students
(B) : 2 students
(C) : 1 student
(D) : 8 students

Success level: 32% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.63

[Version 2] Wezen is a star that has an apparent magnitude of m = +1.8, and an absolute magnitude M_V of –6.9. If Wezen were moved to 10 parsecs away from Earth, its __________ would get brighter.
(A) apparent magnitude m.
(B) absolute magnitude M_V.
(C) (Both of the above choices.)
(D) (None of the above choices.)

Correct answer: (A)

Wezen appears to be +1.8 as seen from its true distance from Earth, but when placed at the "fair" distance of 10 parsecs away, it becomes much brighter (−6.9). Thus Wezen was brought much closer to Earth when moved to 10 parsecs, and was located much farther than 10 parsecs away from Earth. When moved to 10 parsecs away from Earth, its apparent magnitude m would get brighter, while its absolute magnitude M_V would remain the same.

Section 30676
Exam code: quiz04sGf6
(A) : 17 students
(B) : 10 students
(C) : 5 students
(D) : 9 students
No response: 1 student

Success level: 46% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.27