A favorite at Case Western Reserve University where I went to school in the late 1980s was the exploding electrolytic capacitor. In our dorms, there was a switched outlet in the bathrooms above the mirror over the sinks. Most people used it to plug in radios. When you left the bathroom and turned off the light, the radio would automatically turn off, saving electricity.
Well, we would go into the bathroom with a flashlight so we wouldn’t have to turn on the main overhead lights and energize the socket, stick a 47 uF (the optimum value, IIRC) cap into the socket, and wait for the next victim! Flip the switch, light goes on, cap goes boom!
It usually scared the #*$% out of him or her!
One time after a few beers, I didn’t have any caps handy, so I just wrapped some 20 gauge wire tightly around a pen and shoved it in the outlet. It worked nearly as well; instead of an explosion, there was a zap, and a burning, smoking, stinking coil of wire fell into the sink!
While in school we used to place a capacitor across the 600V three phase lines and wait for the teacher to turn on the power. It always got a good laugh when the cap blew. I'm sure the teacher knew what was about to happen as it would have appeared strange to see the entire class wearing safety goggles. I'm most postive he knew but acted clueless anyway. Those were the days.
One of my classmates seemed to be fond of looking in my desk. So I left a well charged electrolitic for him. He picked it up, screaming and shaking his arm as the charge bled down. When it finally allowed him to release his fingers, the cap hit the window with enough velocity to punch a neat little round hole in it.
We had to split the window cost, me for leaving a trap, and him for being stupid.
He still got in my desk. Even after the exlax cookies.
some people are slow learners.
I had a long long discussion working that out.
Fun is when you are on the edge, when you think you are in control but everyone around you think you are not. If things are too easy, that is boring. Too hard, that is frightening. Fun is just that narrow groove.
I once found some full-size Edison-base flashbulbs at a garage sale. They looked just like incandescent bulbs, other than being full of (I think) oxygen and magnesium wool. I had fun screwing them in in place of ordinary light bulbs. When someone flicked the light on - PAFF! Blinding flash!
Giving people a fright is acceptable, putting them in danger is not. As Rod says, it's a pretty narrow groove. Shrapnel from an exploding cap just might get in someone's eye, but it's pretty unlikely.
Someone some time ago talked about someone putting a short on a large electric motor, now that is plain stupid.
The flashbulb thing is pretty funny, but the ones involving capacitors across mains powerlines and high-voltage charged electrolytics are just unbelievably stupid, cruel and dangerous, even for college kids. There are all sorts of ways pranks like that can go badly - or fatally - wrong. It's no wonder we engineers have a reputation as socially inept nitwits.
We had just learned about inductors and reactance in my basic electronics class and after the lecture, one of students came up and asked what I thought would happen if he stuck a small 10uH inductor in the lab bench wall socket (the class also doubled as a lab).
I told him to figure it out, you have 120vac at 60 hertz an that if it was me I would think twice before doing it; I believe the current would be quite high.
By then I was off on the other side of the class talking with my instructor and the other students- and then a BLAM! I can here pieces of the poor inductor ricocheted off the ceiling and walls.
Fortuntely it was the end of class and most students had left.
My respect for instructors in general went up another notch.
You just never know what kind of students you will be getting...
I wonder what job he has now???
A charged condensor from a car's distributor was a favorite for my eigth grade prinicpal. At recess he would walk around on the playground and yell "Here, catch" and toss it to you. We took it as fun and made him teach us how he didn't get shocked himself. This was in 1960. Today, I'm sure that he would be in a lot of trouble. But in my opinion he was a great "hands on" teacher.
Blog Doing Math in FPGAs Tom Burke 18 comments For a recent project, I explored doing "real" (that is, non-integer) math on a Spartan 3 FPGA. FPGAs, by their nature, do integer math. That is, there's no floating-point ...