Flashbulbs, Technology and Permanence. Using the Obsolete to Teach Science

 I set off a flashbulb the other day in science class. My students were so impressed you would have thought I had shown them fire for the first time. And in a sense maybe I had. I set it off with a heavy chrome-plated flashgun that I inherited from my father. My father was a commercial photographer in the 1950’s and 1960‘s. When he died I ended up with a couple of camera cases full of gear including several dozen flashbulbs. My students immediately wanted me to set off another one, which I did, and four or five cell phones immediately appeared in order to record it.

There is some irony in this. We have been studying lightbulbs, the incandescent type, essentially unchanged since Edison. It no longer surprises me that my students don't know how something as ubiquitous and common as a lightbulb works, so we do a lab where they dissect one; they remove the glass, measure and examine the filament, trace the path of the current though it, then turn on the light in the presence of air. It burns white as the sun for an instant then burns out with a puff of smoke.

But unlike the cell phone, incandescent lightbulbs are on the way out. The government has mandated their demise because they are energy hogs. But their immediate replacement, the compact fluorescent, has a trifle of mercury in them and works in a far more mysterious manner than simply using electricity to heat up a thin wire until it glows. So not only are they more confusing to understand, if a teacher had their kids break the spiraled glass to get at one of these bulb’s innards, they could expect a hazmat team to show up in their classroom. 

Since my kids have started doing this lab I have learned there is more to a lightbulb than I would have guessed. There is a built-in fuse to prevent a fire in case of a short circuit within the bulb and like many people, I was under the misconception that lightbulbs had a vacuum to keep oxygen from burning out the filament. Instead they are filled with argon, an inert gas, that has the advantage that its pressure slows the sublimation of the tungsten filament. This sublimation is how a light bulb eventually fails. My students come to understand that since there is no oxygen inside a light bulb really doesn’t "burn out” and what a fine word like sublimation means.

This leads to why I set off the flashbulb. It is a technology even more obsolete than the lightbulb, in fact it is only slightly more advanced than the tray of flash powder it replaced. A flashbulb is a simple affair, they look like a lightbulb but instead of being filled with an inert gas, it is filled with oxygen. And instead of a tungsten filament there is a tuft of finely shredded  aluminum. When a tiny current flows through it it does "burn out" and it does it quickly. It produces a brilliant flash, a flash that left my students awestruck, blinded with a bright yellow shadow before their eyes. The bulb blisters, smokes and it too hot to touch. Growing up I saw my father take many pictures with this very flash gun. It has a red button that ejects the hot bulb and my father would deftly catch them and like a magician make them disappear into the pocket of his suit jacket. 

I was surprised at my student’s enthusiasm because even the cheapest throwaway camera uses a miniature strobe light that is technologically light years ahead of a flashbulb. But while I can talk about the quantum mechanics behind a high voltage electrical field that ionizes the gas in a strobe until gives off light, that is beyond abstract and there is something about the inherent simplicity of flashbulb that allows for understanding. 

Sometimes I wonder if this approach is a good one. A teaching colleague and myself had a spirited discussion that arose over an offhand comment about whether students should learn how a phonograph works. I argued yes, for several reasons. First there is the historical: a phonograph, like a cell phone was a breakthrough technology in its day. 

Second, it is a wonderful opportunity to show a practical application of how a changing magnetic field creates a changing electrical field, something that an amplifier and speakers can turn into sound. It can also show how sound is created by simple vibrations when a student puts a pin in a piece of tagboard and listens carefully as the point traces the spiral grooves of the record. 

But at least as important to me, a phonograph, lightbulb or a flashbulb shows kids that technologies can be understood. Whereas a cell phone, computer, or an iPad are pure magic, they might as well be filled with fairy dust, a thin piece of wire glowing white hot is as primal as fire. A needle vibrating as it rubs on the striations of a record can make the voice of Caruso come alive. 

And there is also the sentimental in showing my students my father’s tools. His flashgun was made for the eternities. It was a tool built as tough as a hammer that demonstrated a belief in permanence. Or, one could equally argue, that it demonstrated a stubbornness, a refusal, to believe that all technology changes. 

But it does have a heft and seriousness to it that most of today’s ephemeral technologies don’t share. And because of that ruggedness it is still works. And because of that I can demonstrate to my students that what they don’t understand doesn’t need to be explained by magic or ignored because it is incomprehensible.