Did you get an "A" on your 7th grade project (the step up transformer)? Also, how did you come up with that idea?
The Tesla coil idea came from a magazine, probably Popular Electronics. It really wasn't hard to build, just tedious to wind the coil. I did it for fun, not for any official project, so I didn't get a grade. But it a good gadget to have around.
When flashbulbs were used with cameras, was there a coil in the camera and a magnet, or how did they get it to light? Also, how are flashes used on cameras today different than flashbulbs?
Flashbulbs contain a wad of very fine magnesium wire that burns almost instantly in a gas of pure oxygen. The wire is ignited by a small piece of gunpowder-like primer material that is itself ignited by the camera. There are/were three techniques for igniting the primer: impact (a little lever smacked the side of a tube containing the primer and it burst into flame, just like a cap), electric current (a thin filament inside the bulb overheated when current ran through it), and spark (a spark jumped between two wires and ignited the primer). The demo I did in class used the current-ignited bulb. We have another demo in which we use static electricity to fire a spark-ignited bulb. A camera that uses/used the current-ignited bulbs has a battery in it and taking a picture closes a circuit that then sends current through the bulb. A camera that uses/used the spark-ignited bulbs used a piezoelectric spark ignitor, like the ones in outdoor gas grills. A camera that uses/used the impact-ignited bulbs just hit the primer itself. Modern cameras uses gas discharges to produce light. We'll discuss these xenon flashlamps in the lecture on Fluorescent Lamps. Since the flashlamp isn't burned up during a flash, it can be used many times.
Why does a moving magnet excite charges?
A moving magnet, which carries with it a magnetic field, creates an electric field. That's just the way our universe works. Changing magnetic fields create electric fields. Since an electric field exerts a force on any electrically charged particle, the charges in a wire are pushed around whenever a magnet moves past them.
How does a magnet induce a metal to become attracted to the magnet? Does the metal become a magnet also?
A steady, motionless magnet can't induce a piece of normal metal (not iron, cobalt, or nickel) to become magnetic. Only a moving or changing magnet can do that. When a metal is exposed to a changing or moving magnet, it does become magnetic. That metal becomes a type of magnet; an electromagnet. The metal itself isn't really the magnet; the electric charges inside it are. These charges move in response to the changing or moving magnet nearby and they become magnetic, too. The effect is always repulsive, not attractive. The temporarily magnetic metal repels the magnet that is making it magnetic.
How can something have small charge moving but large voltage?
When I held my hand near the van der Graaf generator, a spark leaped at it. The current entering my hand was small, but the voltage drop across the air was large. That means that each charge leaping through the air had lots of energy but there weren't very many charges moving each second.
If you keep batteries in your car-where it gets really hot on a summer day-will the batteries "die" faster? (I got brand new batteries and have them in a flashlight in my car and they are almost dead, yet I never really used the flashlight but for a couple of minute.)
Yes. Thermal energy spoils everything and the hotter you heat an object, the more thermal energy it contains. Keeping batteries or photographic film cool preserves them against aging.
The thing you build when you were in 7th grade: is its goal to increase voltage cheaper or without using lots of voltage?
The Tesla coil is a simple but impressive step-up transformer. It isn't of much use itself, but large industrial step-up transformers are very important. They allow a power company to convert medium voltage, medium current power to ultra-high-voltage, low ultra-low-current power. They don't create any power, just rearrange it. The low current then flows through high tension wires to your city, where it is converted back to medium voltage, medium current power for distribution to neighborhoods. In your neighborhood, it's converted again to low voltage, high current power for use in your home.
I have an old car that has a generator instead of an alternator, so I assume it runs DC. What about newer cars? They still use a DC battery right? So what about the alternator? Doesn't that produce AC current? How does that work in a DC circuit?
Generators can produce either DC or AC power, depending on how they're arranged. A car generator was one that produced DC power. An alternator produces AC power. Since all cars operate on DC power (they use a battery, after all), the AC power is always converted to DC power. In modern cars, this is done with electronic devices, similar to those used in electronic equipment such as stereos and televisions. Converting DC to AC or vice versa is no big deal anymore. In the old days, it was harder and they used DC generators.
