All of us love a rainbow, and a double rainbow is even more exciting. This is pchem* in action!
You may have noticed that rainbows only appear with the sun at your back. Why?
Rainbows are angle-dependent. The light coming from behind you hits water drops of a particular size and at a particular angle so that they are diffracted (bent) inside the drop. This can occur in a clockwise or counter clockwise manner. The clockwise path through the drop to your eye and the counter-clockwise path occur at slightly different angles. This creates the two rainbows.
The different wavelengths of light from red to blue also travel at slightly different angles (just like through a prism), and this creates the spread of colors in each rainbow.
Have you ever seen a triple or higher-numbered set of rainbows?
Some will brag and say they have. But this is extremely improbable. If their eyes were sensitive enough to see this higher-order diffraction, then they would be blinded by the bright sunlight needed to produce the rainbow in the first place. The probability of light traveling multiple circles within the water drops to create second- (and higher-) order diffraction effects is very slim compared to the single pass rainbows that we are all familiar with.
Post links to your favorite rainbow images in the comment section.
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*Pchem (Physical Chemistry) is the study of the physical properties of the universe.
Homework serves several purposes in academic pursuits. It guides the students through a subset of material the professor deems important. It forshadows the examination. It serves as a scaffold for the student to assist the building of their body of knowledge in the topic.
It should not be “busy work” because this wastes valuable student time. It should not create a protracted grading burden on the professor, because immediate feedback is best for the student when learning new material.
Therefore, I am exploring the following with positive initial results. I use multiple choice homework problems, because these are automatically graded online by the Blackboard learning system. These assignments fullfil the purposes of forshadowing the exam, and guide the student through the appropriate material.
The negative aspect of this is the natural focus of the student on “which letter is the correct answer”. I do NOT care about which letter they check. I want them struggling with the problems, building their body of knowledge, and internalizing the concepts and theories.
Therefore, I have changed the grading rubric to punish simply getting the correct letters in one setting. The only way to achieve a perfect score on the homework is to do the following:
1. Take the homework exam multiple times over several days showing improvement towards the eventual score of 100%.
One can EASILY fake this, which is why it will only be 5 to 10% of the weighted average of a given course. But instead of faking this apparent activity, consider actively using the process that I am encouraging.
So to my students, I give the following advice:
- As soon as the homework test is made available, log in and take it cold. Give your best guess on the vocabulary. Estimate the numerical answers. Do your best to ace the test “cold” without knowing the material.
- Then, download the pdf version of the homework test. Over the next few days, work the problems in your “problems composition book” (hint, make one of these). Work similar problems from the back of the text. Work similar problems from the Internet. Evaluate why the right answers are right.
- Log back into Blackboard. Take the homework test again. If you do not make 100%, then work the ones that confuse you. Ask about them in class. Get with your study group. If you are convinced your answers are right, perhaps there is an error in the homework test. Ask about it in class.
- Finally, you should be able to achieve a 100% on the homework test, AND THE RECORD OF YOUR MULTIPLE TESTS ON BLACKBOARD will be evidence that you deserve a 100% for PARTICIPATING in the homework assignment.
I welcome your constructive input.
Here is my personal analysis of the Fukushima Daiichi 1 explosion that occurred March 12, 2011. It is possible that the cooling water level in the spent fuel storage pool dropped enough to expose the fuel elements. This could generate hydrogen gas, and is a potential source of the explosion. Hat tip to the Nuclear Energy Institute for providing an image of the reactor design and secondary containment area.
I have created a Prezi to walk you through my thoughts.
I welcome your thoughts in the comments area.
Thanks for watching, and keep praying for the Japanese people as they continue to battle the after effects of this earthquake.
This week in pchem we are discussing the energy minimization techniques that are used in computational chemistry. The students will build a mock energy function that models the dihedral rotation of 1,2-dichloroethane. Then three methods (The Monte Carlo Method, Newton minimization, and Metropolis simulated annealing) will be employed to solve for the preferred (lowest energy) dihedral angle (a).
A performance plot will also be generated that shows the lowest energy and its root mean squared deviation RMSD from the known minimum structure (a = 180 degrees). This plot clearly shows Newton’s propensity to get stuck in local minima. It also clearly shows that the Monte Carlo method will always find the global minimum, but with increasing inefficiency. And finally, the Metropolis simulated annealing technique is found to be flexible enough to accurately locate the minimum energy structure every time provided that the step size and temperatures are “tuned”.
Stay “tuned” for a planned video of the spreadsheet in action.
You can participate! Download the Rosetta@home screen saver, and solve protein folding problems in your sleep. (I have no official connection to the Rosetta at home folks, but their work is great! http://boinc.bakerlab.org/rosetta/)
WordPress is issuing a challenge (to drive traffic of course), and I am going to go for it. Here are the pchem4u blog plans for the 2011 calendar year.
When moving into our new chemistry building, my graduate student uncovered a relic made in the 1930’s. It was a cast-iron Du Nuoy ring tensiometer, but we didn’t know that. We guessed that it had something to do with surface tension, and he did a literature search. Up popped a 1930’s paper by Harkins and Jordan on the ring method for determining surface tension.