Gas station without pumps

2012 October 2

Chapter 14 done

Filed under: home school — gasstationwithoutpumps @ 16:21
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We’re a week behind already, because we did not get any of the Chapter 14 homework done during the trip to Boulder, but we did finally get Chapter 14 done today. The twelve problems I assigned for Chapter 14 (plus one program) were too many, because they were almost all just plug-in-numbers-and-turn-the-crank exercises (despite having been given “P” for problem rather than “X” for exercise). I was rather tired last night and this morning when I did the problems, and I made a huge number of copying errors: copying the charge of an electron wrong (and using it for all the exercises that needed charge of proton or electron), copying the wrong line from a problem, copying numbers wrong from my calculator to the paper, … .  I don’t think I’ve ever had so many wrong answers. On only one problem when my son and I compared answers did we get different results that stemmed from his error rather than mine (and that was also a clerical error, not a conceptual one).

There was one problem that wasn’t just an exercise, though my son treated it as one.  That problem is 14P40 part c:

The electric field at a location C points north, and the magnitude is 1×106 N/C.  Give numerical answers to the following questions:

(c) where should you place a proton and an electron, at equal distances from C, to produce this field.

Locus of positions for electron with C at origin. The proton would be symmetrically located at (x,-y) for an electron located at (x,y). Locus plotted by Wolfram Alpha command “plot y/(x^2+y^2)^(3/2)=347.2E12”

The trivial answer places an electron to the north and a proton to the south, and students just compute the distance. But there are an infinite number of solutions and the locus of the solutions is an interesting one.  I don’t know whether the authors were thinking of this infinite set of solutions, or if they had only considered the trivial solution.

Since C is equidistant from the proton and electron, it must be on the perpendicular bisector of the line segment between them. Since the field points north, and we’re on the perpendicular bisector, the electron must be due north of the proton. If we do a 2D plot, putting C at the origin and the electron at (x,y), we get a formula of the form y/(x^2+y^2)^{3/2}=347.2E12, which we can ask Wolfram Alpha to plot for us. Note: I’m deliberately not providing the derivation for the number, so that students have to do some work before copying this answer!

The trivial solution is the one on the y-axis (not the origin). I had not expected to see the lower part of the curve, where the locus approaches the origin, but it makes sense. If we look at the formula in polar coordinates, we get r = \sqrt{\sin(\theta)/347.2E12}, where r is the distance from C to the electron (and to the proton), and θ is the angle from the horizontal axis (angle north of east). This parameterization also makes it easier to find where the x value is maximized by taking the derivative of \cos(\theta)\sqrt{\sin(\theta)/347.2E12} with respect to θ, and setting it to 0. I get the maximal value for x as about 3.33E-08 m, at about 35.26°.

For very small angles, the electron and proton need to be very close together, though the solutions with them too close together are bogus, because classical electrostatics breaks down once quantum effects become significant.

The polar plot made by giving Wolfram Alpha “polar plot r=sqrt(sin(theta) / 347.2e12)” is cleaner and faster than solving for the x,y values directly.

For next week, we’ll have to read Chapter 15. I should have some problems selected before this weekend.

2012 September 17

Chapter 14 homework

Filed under: home school — gasstationwithoutpumps @ 16:05
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We’re already almost a week behind in physics, having intended to finish Chapter 13 last week, and instead finishing up the homework for tomorrow. We’ve both read Chapter 14, which is a short chapter on electric fields, so we should be able to get back on schedule, finish Chapter 14 by next week (except that my son and I will be visiting my Dad in Boulder Saturday through Tuesday, which will cut into our physics time, so it is highly probable that the schedule will slip again).

Chapter 14 homework—due 2012 Sept 25

14P23, 14P24, 14P40, 14P43, 14P47, 14P51, 14P52, 14P53, 14P70, 14P73, 14P75, 14P76
Computational problem: 14P78

2012 August 31

Physics C: E&M curriculum for year and Chapter 13 homework

Filed under: home school — gasstationwithoutpumps @ 14:28
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I’ll be homeschooling my son in calculus-based physics again this year, using the Matter and Interactions book.  The school  year has started for him, so now I have to put together a schedule for finishing the book this year. I want him prepared  for the AP Physics C: Electricity and Magnetism test in May. We never got around to Chapter 13 last year on thermodynamics, so I’ll tack that onto the beginning of this year’s schedule.

It looks like I have 34 Tuesdays to cover 568 pages, which is about 17 pages a week.  Assuming that each chapter’s length is roughly proportional to how much time it takes to cover it, I’m planning on

Chapter pages weeks Finish by
13 41 2 Sept 11
14 31 2 Sept 25
15 44 3 Oct 16
16 36 2 Oct 30
17 46 3 Nov 20
18 41 2 Dec 4
19 42 3 Jan 1
20 42 2 Jan 15
21 63 4 Feb 12
22 50 3 Feb 26
23 38 2 Mar 12
24 55 4 Apr 9
25 40 2 Apr 23

Chapter 13 homework—due 2012 Sept 11

13P19, 13P20, 13P22, 13P26, 13P27, 13P28, 13P32

We should probably go over the first three problems on 2012 Sept 4 and do a gas pressure lab of some sort (probably pressure and temperature measurements).  I bought some physics toys last spring that may be suitable for the lab.


2012 July 26

Editing Wikipedia for scientists

Filed under: Uncategorized — gasstationwithoutpumps @ 09:28
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Today I got an e-mail message for an interesting workshop associated with the European Conference on Computational Biology. I don’t have the funding to go to Basel this year (I didn’t even go to ISMB in Long Beach), but I agree with Alex Bateman and Daniel Mietchen that it is important for scientists to become Wikipedia editors.  I’ve done a little Wikipedia editing, though not as much as I feel I should. The effort is only internally rewarding—there are no bonus points in academia for writing and editing Wikipedia articles, though they probably have more influence than regular encyclopedias, textbooks, and research monographs combined.

One problem with editing Wikipedia is that it requires fairly frequent visits to undo damage done by ignorant editors, which greatly reduces the internal reward.  Having carefully crafted explanations deleted or mangled repeatedly makes one much less willing to put in the effort to do create them.

===== Call for Participation ======

Editing Wikipedia for scientists
Sunday, 9 September 2012, Basel, Switzerland



We cordially invite you to follow the tutorial “Editing Wikipedia for scientists” held as pre-conference event to ECCB’12 on 9 September 2012 in Basel, Switzerland.

Wikipedia has become an essential repository of scientific information. If anyone is looking for information about your subject area the chances are that a Google search will direct them to the Wikipedia article first. If you would like to get involved in improving Wikipedia content for your subject but never found out how then come to the ECCB Wikipedia tutorial. We’ll show you the basics of editing, as well as telling you how to avoid the common mistakes:

Many people look at Wikipedia as their first port of call for information. Therefore, we believe that it is important for scientists to feel comfortable in editing Wikipedia to ensure it is factually accurate and up to date in their own area of expertise.

Looking forward to seeing you in Basel!

Alex Bateman, Wellcome Trust Sanger Institute, UK.
Daniel Mietchen, EvoMRI Communications.

PS: Please note that you can register for the ECCB tutorials and workshops also without participating to the main conference. Early registration deadline is 1 August 2012.

ECCB’12 – European Conference on Computational Biology 2012
9-12 September 2012, Basel Switzerland

—- Stay informed:
ECCB12 mailing list

2012 July 10

Genetics “Why Do We Have to Learn This Stuff?”

Filed under: Uncategorized — gasstationwithoutpumps @ 21:01
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Rosemary Redfield (Department of Zoology, Life Sciences Institute, University of British Columbia, Vancouver, British Columbia, Canada) has recently published an article in Public Library of Science Biology:  “Why Do We Have to Learn This Stuff?”—A New Genetics for 21st Century Students.

The article outlines problems she sees with the disconnect between the traditional undergrad genetics courses and what biology students really need to learn about genetics.  She also outlines a new course that she thinks should replace the traditional genetics class.  (She does not say whether she has convinced her colleagues at UBC of the wisdom of such a change.)

After outlining the syllabus for the new course, she admits that she expects some pushback:

This radical a change will encounter lots of obstacles. For many geneticists the most upsetting change will be the demotion of genetic analysis from its reigning place in the curriculum. Genetic analysis used to be the most powerful tool for understanding how organisms work, and thus the best skill we could give our students, but its research role has been largely supplanted by molecular methods.

Here, stripped of all the explanation and justification that Prof. Redfield provides, is the core of her proposed curriculum:

Box 4. Suggested Syllabus for a 21st Century Genetics Course

  • Personal genomics
  • Natural genetic variation in populations (humans and others)
  • Structure and function of genes and chromosomes
  • Genetic variation arises by mutation
  • Genetic variation and evolution (selection for function, phylogeny, homologs, gene families)
  • How genes affect phenotypes: pathways, regulatory interactions, heterozygosity, dominance effects (several classes)
  • Genetic variation also arises by chromosome reassortment and homologous recombination
  • Mitosis and meiosis: mechanisms and genetic consequences (several classes)
  • Mating: mechanisms and genetic consequences
  • Linkage and sex linkage
  • Genetic analysis: investigating gene action using inheritance of simple (“Mendelian”) alleles and phenotypes in crosses and pedigrees (several classes)
  • Organelle genetics
  • Epigenetic inheritance
  • Genome structure, function and evolution; causes and consequences of chromosomal changes (several classes)
  • Phenotypic effects of natural genetic differences, heritability
  • Genome-wide association studies and related studies linking genes to phenotypes (several classes)
  • Genetics of cancer; inheritance of alleles affecting risk

I rather like the idea of starting genetics from a population view, rather than a Mendelian analysis of phenotypes, but I think that personal genomics should come a bit later.

Of course, I’ve never taken a genetics class, so I don’t really know which parts of it are essential (or even what is in the standard course). One concept that does seem to be important in reading papers about genomics is the notion of chromosomal distance in centimorgans.  That seems to still be there in the middle of the class (in the lectures on linkage).

I’m curious what people who teach genetics courses or require them as prereqs for their classes think of this shift in emphasis of genetics courses.  What would it gain? What would it lose? Has this sort of change to the course already been tried?

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