Astronomy in-class activity: speed of light and look-back time

Astronomy 210 In-class activity 23 v.16.05.04, spring semester 2016
Cuesta College, San Luis Obispo, CA

Students find their assigned groups of three to four students, and work cooperatively on an in-class activity worksheet on the effect of the finite speed of light on look-back time.

Astronomy midterm question: same luminosity, but different temperature and size stars

Astronomy 210 Midterm 2, spring semester 2016
Cuesta College, San Luis Obispo, CA

An astronomy question on an online discussion board[*] was asked and answered:

??: If two stars have the same luminosity, is it always true that the star with the lower temperature must be bigger?
qcp: Yes, that's true. A cooler star means that it must be bigger to be of equal luminosity.

Discuss why this answer is correct, and how you know this. Explain using Wien's law, the Stefan-Boltzmann law and/or an H-R diagram.

[*] answers.yahoo.com/question/index?qid=20160402221522AAZkrDm.

Solution and grading rubric:

• p:
  Correct. Uses Wien's law, the Stefan-Boltzmann law and/or interprets H-R diagram to demonstrate how a cooler star must be bigger than a hotter star to have the same luminosity.
• r:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
• t:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least discussion demonstrates understanding of Wien's law, H-R diagram and/or the Stefan-Boltzmann law.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least attempts to use Wien's law, H-R diagram and/or the Stefan-Boltzmann law.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion not based on Wien's law, H-R diagram and/or the Stefan-Boltzmann law.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.

Grading distribution:
Section 30674
Exam code: midterm02n4s5
p: 12 students
r: 3 students
t: 3 students
v: 1 student
x: 2 students
y: 1 student
z: 0 students

A sample "p" response (from student 1503), using both the "box method" to fill in relative Stefan-Boltzmann law parameters, along with using the diagonal lines on an H-R diagram to compare size:
A sample "x" response (from student 1096), appealing to recent tragic events in pop culture:

Astronomy midterm question: red dwarf same size as white dwarf?

Astronomy 210 Midterm 2, spring semester 2016
Cuesta College, San Luis Obispo, CA

An astronomy question on an online discussion board[*] was asked and answered:

??: Can a red dwarf have the same size as a white dwarf?
Bpt: They can have the same size if the red dwarf was dimmer than the white dwarf.

Discuss why this answer is correct, and how you know this. Explain using Wien's law, the Stefan-Boltzmann law and/or an H-R diagram.

[*] answers.yahoo.com/question/index?qid=20160402083607AA27vRN.

Solution and grading rubric:

• p:
  Correct. Uses Wien's law, the Stefan-Boltzmann law and/or interprets H-R diagram to demonstrate how a red dwarf can be the same size as a white dwarf by recognizing that:
  1. from Wien's law, the red dwarf is cooler than the white dwarf;
  2. from the Stefan-Boltzmann law (or interpreting an H-R diagram), the lower temperature red dwarf must have a lower luminosity than a white dwarf of the same size.
• r:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
• t:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least discussion demonstrates understanding of Wien's law, H-R diagram and/or the Stefan-Boltzmann law.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least attempts to use Wien's law, H-R diagram and/or the Stefan-Boltzmann law.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion not based on Wien's law, H-R diagram and/or the Stefan-Boltzmann law.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.

Grading distribution:
Section 30676
Exam code: midterm02sLoX
p: 37 students
r: 8 students
t: 4 students
v: 3 students
x: 2 students
y: 0 students
z: 0 students

A sample "p" response (from student 0796), using the "box method" to fill in relative Stefan-Boltzmann law parameters:
A sample "p" response (from student 5713), using the diagonal lines on an H-R diagram to compare size:
A sample "p" response (from student 8041):

Astronomy midterm question: star cluster with white dwarfs?

Astronomy 210 Midterm 2, spring semester 2016
Cuesta College, San Luis Obispo, CA

Discuss which H-R diagram is more likely to be a star cluster with type II supernovae (which are deliberately not shown). Explain using the properties of mass and stellar lifetimes, evolution of stars, and star cluster ages.

Solution and grading rubric:

• p:
  Correct. Understands that:
  1. stars in the same cluster are all born at the same time, but massive stars evolve faster than medium-mass stars, which evolve faster than low-mass stars (the "house party" analogy);
  2. medium-mass stars end their main-sequence lifetimes by becoming giants, planetary nebulae, and then white dwarfs;
  3. such that for medium-mass stars to have reached their end stage, massive stars have already gone through all their stages and have exploded as type II supernovae (and no longer appear on an H-R diagram), while low-mass stars have just begun their main-sequence life as red dwarfs.
• r:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
• t:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. Typically at least understands correlation between mass and main-sequence lifetimes.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Garbled discussion of properties and evolution of stars.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion other than that of the properties and evolution of stars.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.

Grading distribution:
Section 30676
Exam code: midterm02n4s5
p: 3 students
r: 6 students
t: 10 students
v: 3 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response (from student 1503) discussing the "house party model":
Another sample "p" response (from student 1758):

Astronomy midterm question: star cluster with type II supernovae?

Astronomy 210 Midterm 2, spring semester 2016
Cuesta College, San Luis Obispo, CA

Discuss which H-R diagram is more likely to be a star cluster with type II supernovae (which are deliberately not shown). Explain using the properties of mass and stellar lifetimes, evolution of stars, and star cluster ages.

Solution and grading rubric:

• p:
  Correct. Understands that:
  1. stars in the same cluster are all born at the same time, but massive stars evolve faster than medium-mass stars, which evolve faster than low-mass stars (the "house party" analogy);
  2. massive stars end their main-sequence lifetimes by becoming supergiants, then explode as type II supernovae;
  3. such that for massive stars to have reached their end stage, medium-mass have just begun their main-sequence life, while low-mass stars have not yet begun their main-sequence life as red dwarfs.
• r:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
• t:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors. Typically at least understands correlation between mass and main-sequence lifetimes.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Garbled discussion of properties and evolution of stars.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. Discussion other than that of the properties and evolution of stars.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.

Grading distribution:
Section 30676
Exam code: midterm02sLoX
p: 11 students
r: 15 students
t: 23 students
v: 3 students
x: 1 student
y: 0 students
z: 0 students

A sample "p" response (from student 7074) discussing the "house party model":

Physics quiz archive: magnetism, induction

Physics 205B Quiz 6, spring semester 2016
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz06eL3k



Sections 30882, 30883 results

0- 6 :	*   [low = 6]
7-12 :	*****
13-18 :	*********************   [mean = 17.0 +/- 5.1]
19-24 :	**********
25-30 :	*   [high = 27]

Astronomy quiz archive: stellar evolution

Astronomy 210 Quiz 6, spring semester 2016
Cuesta College, San Luis Obispo, CA

Section 30674, version 1
Exam code: quiz06s7ll


Section 30674

0- 8.0 :
8.5-16.0 :	***** [low = 12.0]
16.5-24.0 :	***** [mean = 23.4 +/- 6.2]
24.5-32.0 :	********
32.5-40.0 :	** [high = 33.0]

Section 30676, version 1
Exam code: quiz06nUm6


Section 30676

0- 8.0 :
8.5-16.0 :	******* [low = 8.5]
16.5-24.0 :	************
24.5-32.0 :	****************** [mean = 25.7 +/- 6.2]
32.5-40.0 :	*********** [high = 40.0]

Physics quiz archive: circuits (2)

Physics 205B Quiz 5, spring semester 2016
Cuesta College, San Luis Obispo, CA
Sections 30882, 30883, version 1
Exam code: quiz05Tt1p



Sections 30882, 30883 results

0- 6 :
7-12 :	*** [low = 12]
13-18 :	**************
19-24 :	************* [mean = 20.8 +/- 5.0]
25-30 :	******** [high = 30]

Astronomy quiz archive: sun/spectra/star properties

Astronomy 210 Quiz 5, spring semester 2016
Cuesta College, San Luis Obispo, CA

Section 30674, version 1
Exam code: quiz05nUL7


Section 30674

0- 8.0   :
8.5-16.0 :	*** [low = 12.0]
16.5-24.0 :	*******
24.5-32.0 :	** [mean = 25.9 +/- 8.8]
32.5-40.0 :	******* [high = 40.0]

Section 30676, version 1
Exam code: quiz05sPrB


Section 30676

0- 8.0 :	* [low = 8.0]
8.5-16.0 :	****
16.5-24.0 :	************
24.5-32.0 :	******************* [mean = 27.5 +/- 7.3]
32.5-40.0 :	*************** [high = 40.0]

Physics midterm problem: comparing total electric field magnitudes

Physics 205B Midterm 1, spring semester 2016
Cuesta College, San Luis Obispo, CA

Two point charges are held at fixed locations. A +5 nC charge is at the origin, and a second –1 nC charge is at x = +4 cm. Discuss why the magnitude of the electric field at x = +2 cm is less than the magnitude of the electric field at x = +3 cm. Show your work and explain your reasoning using properties of electric forces, fields, and vector superposition.

Solution and grading rubric:

• p:
  Correct. Discusses/demonstrates that the (total) electric field magnitude would be greater at x = +3 cm than at x = +2 cm by:
  1. evaluating the individual electric field magnitudes E₁ and E₂ created by the source charges Q₁ and Q₂ at each location (four separate terms), and;
  2. discussing how for each location the individual electric field magnitudes add together, as they both point in the same direction to the right (away from Q₁ = +5 nC, and in towards Q₂ = −1 nC), and;
  3. either completely evaluating the total electric field magnitude at each location, or comparing their values in terms of in common relative terms of k, nC, and cm².
• r:
  As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. May have a minor computational error, but at least conclusion is consistent with result.
• t:
  Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. At least some attempt at evaluating electric fields created by each source charge at both locations and vector superposition.
• v:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Some garbled attempt at applying electric forces, fields, and vector superposition.
• x:
  Implementation/application of ideas, but credit given for effort rather than merit. No clear attempt at applying electric forces, fields, and vector superposition.
• y:
  Irrelevant discussion/effectively blank.
• z:
  Blank.
  

Grading distribution:
Sections 30882, 30883
Exam code: midterm01rx1C
p: 22 students
r: 7 students
t: 8 students
v: 4 students
x: 2 student
y: 0 students
z: 0 students

A sample "p" response (from student 0001), explicitly evaluating the electric field magnitudes:
A sample "p" response (from student 0720), eliminating common factors:>