Petaluma High School, in the late 1960s and early 1970s had a great Electronics Engineering teacher. I’d have to dig out a buried year book to retrieve his first name, but we always called him, Mr. Webster. His lectures and labs were both informative and fun and he pretty much invited us to insert a certain amount of what might be called, malicious inquiry.
“Today we’re starting a new section that begins with magnetism before moving into electromagnetism.” After saying this to us, he pulls out a huge horseshoe magnet and allows it to drop onto his lecture desk with a loud THUMP. We all jump some at the sound. He then demonstrates how some materials are attracted to the magnet while others weren’t.
He then pulls out a smaller bar magnet to demonstrate the magnetic field with iron filings. We’d all seen that dozens of times before, but he wanted to make a point.
“Does anyone know where we might find the biggest magnet in the whole world? Ah- Joyce, what do you think?”
Joyce was one of our brainy-acks. “The world itself is the biggest magnet in the world.“
“Correct! and here’s a chart that illustrates how the globe of earth is much like a bar magnet in how the magnetic lines of flux flow from the south pole to the north.”
We also had a few smart alecs in the class who could not resist a possible chance to embarrass Mr. Webster. With his hand raised, one interrupts “I’m confused.” He gets out of his seat and walks to the front of the room and stands behind the large horseshoe magnet and picks up an iron rod and a wooden dowel. “You said that some materials are not affected by magnetism.” He lowers both until the huge magnet snaps the iron rod down with a loud CRACK. He then moves the wooden rod back and forth – demonstrating again how the wood is unaffected.
“Yes, that’s all correct, so what’s the confusion?”
“I think the wood IS affected by the magnet, but this one isn’t big enough…” he straightens out his arm to one side and drops the wood rod, which falls to the ground. “because the biggest magnet in the world affects it just fine.”
Smart alec, returns to his seat under the playful glare of Mr. Webster and a growing wave of student snickering. “Mr. Wilson,” he carefully says, “that was gravity.”
“Oh. Okay, what’s gravity then?”
Oddly enough, Mr. Webster did not then know what even physicists today don’t completely understand and I caught him without the words needed to distinguish magnetism from gravity. Odder still – was that I wasn’t thrown out of class. I think there was an unwritten rule about how if you get enough student laughs without being rude, you could get away with almost anything vaguely scientific in Mr. Webster’s classes.
In high school, many of us began to worry about what we were going to do when we grew up. I only knew that I wanted my work life to involve electronics somehow. Fortunately, Petaluma High had Mr. Webster who not only loved the topic but also loved his students. But his type of love would not be allowed these days because – well – some might judge his displays of affection inappropriate by today’s standards.
Now that I have your full attention – you need to calm down, because this is not one of those stories. I don’t have one of THOSE stories.
My peers in this class were more like a gang of friends following our instructor. We learned lots about the topic and had lots of laughs along the way. There were also more than a few stray sparks dancing around defying reasonable control.
As we went through the topics of electronics, we learned about the normal components and in particular the humble “capacitor”, often called simply a “cap”. To make sure you can enjoy the full impact of this retelling, you need to have a minimal understanding of what a capacitor does. In short, you know about a normal battery:
- two poles, +positive and -negative
- full of “electricity”,
- trying to get from one pole to the other.
Well a capacitor is just like a battery that stores electricity but not as much. A battery of equivalent size might be able to run something for a relatively long time but a capacitor can do the same thing for only very short time. Capacitors are designed to be quickly charged and discharged often – over and over. They come in a variety of sizes and some can hold scary fun amounts of electricity.
One afternoon, after the main class was dismissed and some of us were hanging around playing with the class capacitor collection, I found a big one in the box and we all know that the biggest had to be the best. This cap was designed to have one contact coming out the bottom and the other contact was the metal case – not too unusual, but key to this story. We were charging various capacitors with the class power supply then discharging them against a metal shelf post that stretched across the front of our work benches. Each time we were rewarded with a cool, loud spark.
You know that electricity needs a complete circuit to flow and the post was great for this. I would charge my capacitor, lean the main contact against the post then tilt the case against the post to complete the circuit – easy – right? Well, I got good at doing this real fast and started carelessly putting my left elbow up on the wooden shelf as I sparked my cap each time. Unknown to me was how these shelves were constructed. The builders used metal screws from the top of the shelf down through the wood to meet a round metal plate into which was screwed the metal poles we were using. Queue the dark music of impending doom…
My capacitor held all of 300 volts, so it made a huge spark, but the last time that capacitor and I did business…
- I held it by the metal case (part of the circuit) and charged it from the power supply,
- disconnected from the power supply and moved over to the post,
- put my elbow up on the shelf where it was touching one of the screws holding the posts.
- See the problem coming now?
- Touched the single contact of the capacitor to the post and – VIOLA!
- I had completed the circuit – just not the one I intended.
- This circuit went from my right hand holding the metal capacitor case,
- up my right arm,
- across my chest,
- down my left arm to the point near my elbow where the circuit continued,
- down one of those screws to the top of the same post where I had just touched the contact so, – ZAP –
- I took the full 300 volts across my arms and chest,
- almost explosively.
I can now testify that a quarter second of 300 volts is fully able to pick you up and throw you backwards for at least 4 feet – maybe further, but that’s where I slammed into one of those tall metal cabinets – which was about the same time that my confused consciousness resumed by wondering what just happened and why my arms and legs were waving behind me like something out of a cartoon. The metal cabinet made a huge crashing noise and I then fell down to the floor with my heart performing an emergency reboot to regain normal functionality.
Wow! What a rush – a very – very unpleasant rush. Anyway, can you imagine what would unfold if this happened today:
- 911 would be called,
- cell phones would pop out to record the event,
- campus security and parents would be contacted and statements taken from all present.
- I would have had an EMT rush me off to a hospital for serious medical once-over and
- a counselor would on me within the hour and an agonizing discussion would be extracted about my feelings … (Sir – I’m just glad to be alive already…)
- followed by a parade of attorneys anxious to carry my case to huge taxable income events for both them and me,
- all before Mr. Webster was handcuffed and perp-walked off campus straight to jail and to the front page of every on-line news source for public execution – right?
Not so back then. All my peer students and Mr. Webster laughed – hard, and that was expected – even if it took me about half an hour to be able to laugh at anything. My best friends, most of whom were in the room with me – took no end of pleasure in reminding me how aerodynamic I had been.
Finally – I don’t recall that the event was important enough to mention to my parents.
This event was life changing in that I never – ever – took a capacitor, or anything else that holds that kind of electrical charge for granted ever again. That instructor remained one of my best adult friends for a long time and the time I spent in his classes were some of my best times at Petaluma High School.