Posted in Education, Physical Chemistry, Science Education, Spectroscopy

What is pchem?

Pchem is short for Physical Chemistry. It is hated by all. It is SO bad (the audience asks, “How bad is it?”), that it has it’s own bumper sticker!
Why is pchem so mistreated?
Like a scientific tax accountant, a P-chemist worries about the energetic balance sheet, the gains and losses of energy, the ratio of usable to unusable energy. We pull the thread through all states of matter – liquid, solid, gas, plasma, elastic, plastic, glass, etc.
My favorite subsection of pchem is symmetry and spectroscopy. Spectroscopy is the study of light interacting with matter. And symmetry is used to decipher these interactions. There is no better example of the mathematical beauty of our universe than the unexpected explanatory power of group theory as it applies to absorption and emission of light.
Fireworks, hair dye, crayons, ink, glow sticks, lightning bugs, and all the rest can be understood through pchem – specifically my field of spectroscopy.
There is much more to pchem. If you have made it this far, then you are truly curious. Therefore, I give you the table of contents to a typical pchem textbook. (You will have to “Look Inside” at the Amazon site to view the TOC.)
And, I ask you to share and subscribe to this blog. Comment below with suggestions for posts.
Posted in Education, Spectroscopy, UV-VIS-NIR

What makes a rainbow?

All of us love a rainbow, and a double rainbow is even more exciting. This is pchem* in action!

A double rainbow photographed in Karlsruhe on July 22, 2011. Leonardo Weiss

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.