Avogadro's number: 6.02X10^23 ions per mole. The Faraday constant: 96,500 coulombs per mole. The charge on an electron: 1.6E-19 coulombs per electron.
Why this post? A small illustration. The background is this: A college physics exam, "cheat sheet" allowed. I brought my cheat sheet, but it had an omission that resulted in consternation during the exam. For a particular question, I _needed_ to use the fundamental charge on the electron. Sorry, I don't recall the exact question, maybe because it was over 40 years ago. But I clearly recall the process I used to address this particular problem because I had neglected to write down this fundamental constant on my cheat sheet. Panic! Woe! At least, initially. Then I thought about it. I did have some information that would allow me to calculate the charge of an electron. Yes, I was fairly certain that I knew the value: but I was in a bit of a panic at the time. How to verify? I happened to have two other important constants on my cheat sheet (but I was certain of them anyway). One was Avogadro's number, the number of atoms per mole of a substance: 6.02X10^23. And the other number, Faraday's constant, which gives the number of coulombs ( a measure of charge) per mole. Dividing Faraday's number by Avogadro's number gave me the charge on a single ion AKA electron: 1.6X10-19.
I used the calculation to solve that particular test question.
Why would anyone be interested in Faraday's constant, other than someone with a peculiar memory for odd physical constants?
Two industries come to mind. One is the electroplating industry. If we know the surface area of something we want to plate, and the thickness we wish, we can use Faraday's constant to calculate the current * time needed to get that thickness. Oh, yeah: Q (coulombs) = current * time. Why is this important? What if you're plating something expensive, like silver. Electroplaters made a shitpot of electroplated silver pieces for folks because it was relatively cheap: but they needed to very precisely manufacture the pieces, including the thickness of that precious silver layer...too thick and they lost money, too thin and the pieces wore out too soon. Faraday to the rescue.
Another industry: the infant electric utilities. They needed to know how much electricity they had delivered to each customer. If they diverted a small percentage of the delivered current to an electroplating cell, they could determine the amount of power consumed by weighing the amount of silver that had been plated.
In both cases, capitalism demanded it: and physics delivered.
While it might seem that physics and the real world have significantly parted ways lately, that's far from the truth. The LED light bulb is a great illustration (pun intended) of this. It is a story of many different disciplines. I will likely elaborate on this in another post.
Quiz time. Here's another useful "constant" I use regularly: .301030. What is it? No, it's not found in physics or chemistry.
Sunday, March 29, 2015
Kickoff of Dabblers Lair
For some time I've been thinking about a blog that describes my various tech-centric (mostly) activities. Done not in the vein of trumpeting the victories but as a process of taking a concept or thought and making it real. Or analyzing it and concluding it's impractical or impossible.
My interests have a broad range. Here is an incomplete list.
Machining, as a process of learning how to shape metals and plastics accurately, with few-to-none of those "oh s**t" moments when you figure out you just blew several days of machining.
Nitrogen vacancy centers (NV centers) in diamond. An elegant quantum-mechanical system that could find its way into applications like quantum computing, supersensitive magnetometers, MRI, etc. A system that is relatively easy to experiment with (I think), given a few items available off of Ebay, Amazon and Edmund Optics.
Mathematics. Example: I recently have become interested in the mini-Kossel type of 3D printer. It is elegant in its own way, because the XYZ movements are accomplished by combining 3 identical actuator mechanisms. Conventional XYZ printers use an XY table, with all its foibles, and a Z gantry, also with interesting issues. However, mathematical analysis of the Kossel has shown that its resolution depends on the current position of the printer head. I think the specifications shown for Kossel-based 3D printers are best-case and don't necessarily reflect what users will experience.
Chemistry. I ran across a reference to "magnesium oil", which is used as a topical source of dietary magnesium. If you browse the 'Net for health supplements you will find information which suggests that everyone is short of every element under the sun (literally). My interest was picqued because I was not aware of any benign organo-magnesium compounds. A lot of organo-metallic compounds do things like spontaneously combust in air (like diethyl zinc), or are horribly toxic, like methylmercury. So what is magnesium oil? Turns out it is a fairly concentrated solution of magnesium chloride. Applied topically, it is easily absorbed through. Turns out that it is easy to make using table salt (sodium chloride) and epsom salt (magnesium sulfate).
Here's how it is done. Make two saturated solutions of table salt and epsom salt. Mix the "right" volume of each one so each magnesium ion has two chloride ions available to it. This can be done by looking up the solubility constants for each, calculating the molarity of the resultant solutions and....the rest is left as an exercise for the student <heh>. Now throw the combined solution in your freezer and wait a day or so. The magnesium chloride crystallizes out of solution because its solubility greatly decreases at low temperature. Working quickly, strain out the crystals. Voila, magnesium chloride, which can be redissolved & used for "magnesium oil".
And on and on.
MK 3-29-15
My interests have a broad range. Here is an incomplete list.
Machining, as a process of learning how to shape metals and plastics accurately, with few-to-none of those "oh s**t" moments when you figure out you just blew several days of machining.
Nitrogen vacancy centers (NV centers) in diamond. An elegant quantum-mechanical system that could find its way into applications like quantum computing, supersensitive magnetometers, MRI, etc. A system that is relatively easy to experiment with (I think), given a few items available off of Ebay, Amazon and Edmund Optics.
Mathematics. Example: I recently have become interested in the mini-Kossel type of 3D printer. It is elegant in its own way, because the XYZ movements are accomplished by combining 3 identical actuator mechanisms. Conventional XYZ printers use an XY table, with all its foibles, and a Z gantry, also with interesting issues. However, mathematical analysis of the Kossel has shown that its resolution depends on the current position of the printer head. I think the specifications shown for Kossel-based 3D printers are best-case and don't necessarily reflect what users will experience.
Chemistry. I ran across a reference to "magnesium oil", which is used as a topical source of dietary magnesium. If you browse the 'Net for health supplements you will find information which suggests that everyone is short of every element under the sun (literally). My interest was picqued because I was not aware of any benign organo-magnesium compounds. A lot of organo-metallic compounds do things like spontaneously combust in air (like diethyl zinc), or are horribly toxic, like methylmercury. So what is magnesium oil? Turns out it is a fairly concentrated solution of magnesium chloride. Applied topically, it is easily absorbed through. Turns out that it is easy to make using table salt (sodium chloride) and epsom salt (magnesium sulfate).
Here's how it is done. Make two saturated solutions of table salt and epsom salt. Mix the "right" volume of each one so each magnesium ion has two chloride ions available to it. This can be done by looking up the solubility constants for each, calculating the molarity of the resultant solutions and....the rest is left as an exercise for the student <heh>. Now throw the combined solution in your freezer and wait a day or so. The magnesium chloride crystallizes out of solution because its solubility greatly decreases at low temperature. Working quickly, strain out the crystals. Voila, magnesium chloride, which can be redissolved & used for "magnesium oil".
And on and on.
MK 3-29-15
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