To show my electrician apprentices the danger of fire from, say, car batteries, I would sharpen a half length H pencil at both ends and connect it with crock clips across a 12V car battery or similar, capable of supplying a couple of amps. The pencil would be about 6 to 12 Ω and about 1 or 2 amp would flow resulting in a power dissipation of 12 to 24 watts. The graphite in the pencil would heat up and after 30 seconds or so the paint on the pencil would start bubbling and lovely delicate smoke spirals start to emit from the pencil ends. Then the pencil would issue small flames from the ends, with the wooden body of the pencil finally and dramatically bursting fully into flames and falling off the graphite in two halves, leaving the graphite itself glowing red hot.
My apprentices were happy to accept the dangers from electrocution but not all of them seemed to understand the dangers from low voltage high current until this brought it home to them.
Two things worried me about the demo though. The first being that they would go and show it their friends and burn down their car, house or garage! The other was that the burning paint can be quite toxic and can certainly set an asthmatic off. I would stage the demo outside or in a fume cupboard if I could get hold of one.
I inherited from my grandfather an amazing power transformer with multiple low-voltage taps. I have no idea what its original purpose was, but at the time I was interested in what effect electricity would have on ordinary tap water. IIRC, I was maybe seven or eight years old at the time and living with my grandparents in Tennessee while my mother recovered from tuberculosis at an army hospital in Aurora, Colorado. This was about the same time that the "miracle drug" streptomycin was first used to treat TB patients, but in the year or so it took to kill the tuberculosis bacteria in her lungs, I got to play with electricity as taught by Grandfather, a retired coal mine electrician.
So, to do the water experiments, I needed a pair of electrodes. At first I salvaged carbon rods from discharged dry-cells, but later decided that thinner carbon rods would (somehow) work "better". I had no idea then that what I was attempting to do was called electrolysis, and that it normally requires DC, not AC. And of course I had no test equipment, nada, not even a voltmeter. Still, with the transformer connected to the rods, and the rods inserted into a Mason jar containing water, interesting things happened.
I discovered that the pencil leads I finally used would get red hot when the opposite ends of a pencil (with the wood removed on each end using a pocket knife) were connected to appropriate leads on the transformer. Amazing stuff for a kid my age to discover, but I had no interest in demonstrations for my grandparents or anyone else, mainly because I had no explanati9n of what was going on!
It would be "politically incorrect" for me to suggest that youngsters should try experimenting with water and carbon "leads" electrically separated from their wooden shells if they happen to have a doorbell transformer handy... but I would gladly have let my kids do what I did if any of them ever showed an iota of interest, which they didn't. <sigh>
My oldest son did eventually go to college and became a graduate electrical engineer, but he may have chosen that profession for reasons other than the fact that his father did the same thing. He could just as easily have become a physicist or a mathematician or almost anything involving involving science.
Thanks for the post. It brought back some happy memories.
