In the course of science education every student should get the chance to see a Van De Graaff Generatoror Tesla Coil in action. These electrical devices are a fun way to demonstrate properties of electricity. At Spectrum Scientifics we have recently added several new such devices to our offerings. So let’s talk about the Van De Graaffs first!
Van De Graaff Generators: Often referred to as a ‘static generator’ or ‘that thing that makes your hair stand up’ the Van de Graaff emplyes a belt that carries a positive charge to the ball at the top of the generator. This ball gives the generator its classic shape:
The Van De Graaff opeartes by the moving belt ‘pulling’ charges from the lower electrode (which is effectively grounded and can pull as many charges as needed) in the long narrow tube. These are carried up the tube on the belt and picked up by another electrode (which can only get the charges picked up on the belt). This electrode is connected to the ball at the top. When the charge reaches the top is spreads out along the ball. This charge can then be discharged by using a grounded wand (usually attached to the Van de Graaff unit) resulting in an impressive crack and tiny bolt of lightning.
Alternatively, the static charge built up on the charge can be used to show other fun effects of static charge: a bowl of puffed rice can be sent in a shower of cereal, mylar streamers can be made to fly or spin, and of course a person who is ungrounded can touch the ball and recieve the charge which can make their hair (always vulnerable to static charge) stand up on end.
Spectrum Scientifics has several models to choose from to suit customer needs. Our basic model does quite well:
This model may require an external variac for speed control (otherwise it will run at full speed), and includes a discharge wand. It is a good model, small sized and budgeted for middle school/early high school applications.
For those on a budget, the Eisco Hand Operated Generator may be a good choice.
While this model is operated by hand, it is much larger and has a much higher potential than our basic model. The hand crank system may be concern to some but the operation is almost as good as a motor driven unit (at least over the short term) and there is no concern about speed control as the demonstrator is in control of the generator speed at all times.
For those with a bit more budget the Eisco Motor Driven Generator may be more useful:
This unit may also require a variac to control the speed, but the motor drive will opearte without making your arms tired.
Van De Graaff generators can be notoriously finicky and in an upcoming entry in this blog we will cover how to get one working at its best. But for now we move onto the other fun science glass electrical item: Tesla Coils!
Tesla coils need to be plugged in as they convert wall electricity into high voltage, low-current, high frequency electricity. This electricity forms a field around the top of the Coil and can have some interesting effects. Especially when your Tesla Coil is on the large size and can discharge that field:
Tesla Coil discharges are nothing to mess with, even with smaller models, at least directly. The immediate discharge can actually hurt you but if it goes through something else first (such as a wire or bulb) the high frequency nature of the Tesal electricty means it will travel around your body, and not through it
By comparison, the discharges from a Van De Graaff are pretty much harmless. That being said, you can have loads of fun with the discharge from a Tesla coil: Interfereing with AM radio reception (short range only), light light bulbs, and much more. Here are some videos:
Spectrum Sells the model shown in the image above. A simple, yet effective Tabletop Model that works well for most classroom needs. Larger tesla coils you see are either custom jobs or homebrew models.
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