Brain Teaser Challenge - February 2004

Butch Shadwell

The other day as I was reading a book about medieval England, I fell asleep and had the most realistic dream. In this dream I was a famous knight. I was known throughout Europe for my unmatched skill with the sword and lance. The dream was so realistic, I found myself often gasping from the pungent odors from everywhere and everyone. This was not a bad dream, as dreams go. After having been named MVP on the tournament circuit for the last five years I had collected some great endorsement deals, set myself up with a huge castle, and was having to beat off the jousting groupies with a stick. Except for the constant danger of getting my head cracked with a lance, and of course the smell, it was a pretty good life.

In order to impress the local wizard, I thought I would make a fire start magically. Somehow my dream alter ego found a 9 volt alkaline battery, and managed to recall that they have an output impedance of about 18 ohms. I did mention that this was a dream right? Anyway my medieval self thought about taking the battery and attaching a length of wire to make a heating element with which to light a fire. Unfortunately, probably due to a few to many head shots with a lance, I couldn’t remember what resistance the wire should be to get the most power out of this battery to generate heat in my little wire fire starter. I’m sure that all of my readers know the answer to this one. What is the optimal resistance of me olde heating coil?

Reply to Butch Shadwell by March 1 at (email), 904-223-4510 (fax), 904-223-4465 (voice), 3308 Queen Palm Dr., Jacksonville, FL 32250-2328. ( The names of correct respondents may be mentioned in a future solution column. The solution will be available after March 15 on the web at

Brain Teaser Challenge Solution - January 2004

Due to the publishing schedule, at the time I am writing this I have only received one correct answer for this BTC. If you recall last month I was acquainting you with my cousin Otis and “these vacuum tubes (that) were named for the fruit/nut of a common tree. With just this much information, can you tell me what the common name for this type of tube was? And to really impress me, what were the five leads connected to inside the envelope?”

Of course the old timers in the audience immediately recognized “acorn” tubes. They were used in many applications that required very small size and perhaps higher resistance to vibration. Charles Lord sent me the attached photo. As you can see, two leads were for the heater, one lead was the cathode, one lead was the grid, and the last one was to the plate or anode. I started working in electronics 40 years ago, and the engineers of that era and before were brilliant. When I think about some of the great designs our predecessors did with such limited technology, those guys were real pioneers. I hope that that creative genius and tenacity is still alive in our numbers today.

IEEE Region 3 eNewsletter Volume 19 No. 2, February 2004, © 2004 IEEE
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