American readers of this blog can be forgiven for considering Benjamin Franklin (1706-1790) primarily as a statesman. Admittedly he did some minor things along this line: helping draft the United States’ Declaration of Independence and serving as the ambassador to France where he secured support for the American War of Independence. Franklin was even the country’s Postmaster General at a time when the postal service was important, not delivering mostly junk-mail. But the show’s writers know what Sheldon knows, that Benjamin Franklin was a major physicist.
Franklin’s interest in electricity began with electrocuting turkeys for his friends’ amusement, but after once shocking himself unconscious he concentrated on more scientific endeavors. In tonight’s episode, Sheldon enumerated three of Franklin’s inventions: Using the principles of thermodynamics, Franklin invented the “Franklin stove”, which transfers more warm air to a room than an ordinary fireplace, while still satisfying the important detail that the poisonous exhaust exit the chimney. Using the principles of optics, Franklin made “bifocal lenses”, which contain glass with its upper and lower parts ground with different curvatures so that they bend light at steeper or narrower angles. Such different focusing powers allow the wearer of spectacles to focus on either near or far work without changing glasses–while efficiently allowing us the rest of us to identify people over the age of 43. Franklin’s “flexible urinary catheter” is an invention best left to the websites that focus on such things specifically.
Electrocuted turkeys notwithstanding, Franklin’s most significant scientific work was in the field of electricity. In Franklin’s time, two distinct forms of electricity were known and identified as two separate fluids: vitreous and resinous, named after the material it came from. Vitreous electricity can be produced by rubbing glass with silk (“vitreum” being Latin for “glass”) and resinous electricity charge can be produced by amber resin with fur (“resin” being English for “resin”). Franklin noticed a conservation law between the two types of fluids whenever they were generated. He speculated that rather than creating two separate electrical fluids with rubbing, a single electrical fluid was in all material and merely redistributed by rubbing. He speculated that vitreous electricity was an excess of this single fluid and resinous its deficit. A one-fluid theory is correct for nearly all electricity we encounter. The so-called resinous electrical fluid turned out to be the flow electrons while the so-called vitreous fluid is just the remainder of the atoms left behind. For example, in the copper wires in your house, the fluid that flows is really electrons. But there was one “gotcha”. Franklin had a 50/50 chance to guess which fluid was the excess and which the deficit—and he got it wrong. Ever since, the sign physicists apply to the charge of an electron is negative. In a circuit, the flow of the electrons is exactly opposite what is labeled the electric current. That tricky minus sign survives to this day, allowing me and my colleagues to confuse a new set of physics students every year.
The speed of the fluid in copper, that is the speed of the electrons in a copper wire, is a remarkably slow quarter-inch per second. Yet when you turn on the light switch in a room, the lights appear immediately. So, how can a light switch work so fast? The analogy I give my students is turning on the hot water faucet in their shower. The water immediate flows because the pipes are full of water, but notice the water starts cold. It still takes up to a minute for the hot water, which has to flow from the hot water heater, to reach the shower. The same is true for electrons in your house wiring. The copper wires are filled with with electrons and the the power company’s generator is pushing on the electrons at its end of the wire. When the switch is closed (“turned on”), that push on the long line of electrons pushes on the electrons in your lightswitch, and in turn in the wire inside the lightbulb, producing light. The push is what matters. If it were direct current, the time for the electrons themselves to travel from the power company to your light would take about a year. (Since it is really alternating current the electrons just slosh back and forth 60 times per second–50 times for our friends abroad.)
Ultimately, the two-fluid model turned out not to be wrong. Modern experiments, such as those of Barry Kripke, Sheldon’s nemesis, produce materials called plasmas. Plasmas are created when you heat a material so high that the negative electrons break free of the positively charged atomic nucleus in each atom and even the atomic nuclei break free of each other. In a plasma, both the negatively charged electrons and the positively charged nuclei in a plasma move freely. Plasma physics experiments like Kripke’s manipulate both types of electrical fluids.
At the time, Franklin described his reaction to his discoveries as “Chagrin’d a little that we have hitherto been able to discover nothing in this way of use to mankind”. Given how important electricity is to modern life, his words remind us that the fruits of fundamental research to humanity are not always immediately apparent.
Wolowitz wraps up their Benjamin Franklin discussion with “To learn more about our founding fathers visit your local public library.” That was highly appropriate since Franklin founded the first lending library in America, the predecessor to our free public libraries. Franklin’s electrical work is honored to this day by the naming of the official unit of charge (in the centimeters-grams-seconds system) as the “franklin” (Fr). To learn more about electricity, visit your local public library.