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Astronomy clicker question: protostar to main sequence evolution

Astronomy 10, Spring Semester 2007
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal Q9.5

Students were asked the following clicker question (Classroom Performance System, einstruction.com) in the middle of their learning cycle:

[0.3 points.] How is it possible for the luminosity of a protostar to remain (approximately) constant as it becomes a main sequence star?
(A) Its surface temperature gets hotter as its size gets smaller.
(B) Its surface temperature gets cooler as its size gets smaller.
(C) Its surface temperature gets hotter as its size gets larger.
(D) Its surface temperature gets cooler as its size gets larger.

Correct answer: (A).

The evolutionary track of a protostar as it becomes a main sequence star can be approximated as a horizontal path from right-to-left across an H-R diagram, which means that its luminosity remains constant while its surface temperature increases. From the Stefan-Boltzmann law, constant luminosity means that size must decrease while temperature increases.

Student responses
Section 4136
(A) : 19 students
(B) : 2 students
(C) : 7 students
(D) : 1 student

Student responses
Section 5076
(A) : 7 students
(B) : 0 students
(C) : 13 students
(D) : 1 student

1 comment:

Patrick M. Len said...

Astronomy 10, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Student responses
Section 4160
(A) : 14 students
(B) : 2 students
(C) : 4 students
(D) : 9 students

Section 5166
(A) : 24 students
(B) : 4 students
(C) : 9 students
(D) : 2 students