tag:techtv.mit.edu,:Array/186464500 2009-01-14 12:37:06 -0500 MIT Department of Physics Technical Services Group A <a href="http://en.wikipedia.org/wiki/Wimshurst_machine">Wimshurst electrostatic generator</a>, working on the principle of induction, generates high voltage differences and sparks between two movable electrodes. By increasing the distance between the electrodes, higher potential differences can be built up. <br><br> <a href="http://en.wikipedia.org/wiki/Electrostatic_induction">Electrostatic induction</a> refers to the principle that charges in an object (especially a conductor) redistribute themselves in the presence of nearby charges. Opposite charges are attracted to each other, while similar charges are repelled. <br><br> Larger charges can be stored by connecting the knobs to Leyden jars which are component parts of the machine. 151 tag:techtv.mit.edu,:Array/186281420 2009-01-16 16:22:08 -0500 MIT Department of Physics Technical Services Group Paper confetti is placed atop a <a href="http://en.wikipedia.org/wiki/Van_de_Graaff_generator">Van de Graaff generator</a> and flies off when the grounding rod is removed. <br><br> When turned on, a Van de Graaff generator builds up lots of negative charge on its large metal sphere. A grounding rod is used to protect the demonstrator and control the amount of charge. When the paper confetti is place on the sphere the charge jumps onto it, but since paper is an insulator, the charge cannot move and sticks to the inner side of the paper. Since there is more negative charge also on the sphere, the negatively-charged paper will be repelled away. <br><br> The Van de Graaff generator was developed by <a href="http://en.wikipedia.org/wiki/Van_de_Graaff_generator">Robert J. Van de Graaff</a>, an MIT professor. 0 tag:techtv.mit.edu,:Array/186184140 2009-01-16 16:40:13 -0500 MIT Department of Physics Technical Services Group First, a dipole consisting of two conducting balls connected by an insulating rod swings at the end of a long plexiglass rod. The two balls are charged oppositely by touching it to a conducting rod in the field of a Van de Graaff generator. The generator is negatively charged, which induces a positive charge on the closer silver ball, and a negative charge on the further gray ball. Going around the generator, the dipole always aligns itself with the electric field, i.e. the silver ball always stays closest to the generator. <br><br> Next, the Van de Graaff generator induces a positive charge on the closer side of a helium-filled conducting balloon, attracting it towards the generator. When it touches the generator, it picks up a net negative charge and is repelled away. When it hits the demonstrator (who can be thought of as "ground"), the net negative charge is removed and it is once again attracted to the generator. <br><br> The last clip combines these two ideas. The two outer bells are connected by a conducting rod and form a dipole in the field of the Van de Graaff generator, while the inner bell is grounded. The small balls are attracted to the outer bells the same way that the balloon was attracted to the generator. Once the balls hit the outer bells, they pick up a net charge and are repelled away. When the balls hit the grounded bell they lose their net charge and are attracted back to the outer bells. As you can see, the chimes do not work when the Van de Graaff generator is grounded. <br><br> A Van de Graaff generator is a machine that produces a lot of charge (in our case negative) on the outside of a conducting sphere. It was developed by <a href="http://en.wikipedia.org/wiki/Van_de_Graaff_generator">Robert J. Van de Graaff</a>, an MIT professor. 172 tag:techtv.mit.edu,:Array/186133380 2009-01-22 15:13:38 -0500 MIT Department of Physics Technical Services Group <a href="http://en.wikipedia.org/wiki/Leyden_jar">Leyden Jars</a>, an early style of capacitor, can be connected to the two electrodes of the Wimshurst Machine. They will store charge as it is generated, giving a much stronger spark across the gap. <br><br> Next we have a three-piece dissectible Leyden Jar consisting of two metal cups separated by a glass cup. When charged with the Wimshurst machine, we see by touching it with the shorting rod that it holds a large amount of charge. However, when disassembled, the metal cups can be brought into contact with each other and no spark will be generated. When the jar is reassembled it can then be discharged. This demonstrates that, in this situation, the charge actually resides on the surface of the glass (a <a href="http://en.wikipedia.org/wiki/Dielectric">dielectric</a>), not on the metal. 175 tag:techtv.mit.edu,:Array/186084620 2009-02-24 14:43:29 -0500 MIT Department of Physics Technical Services Group In the electric field of a Van de Graaff generator, an unprotected Ben Franklin feels electrostatic forces. However, when a metal cage surrounds him, he is completely shielded against any electricity or electrostatic force. <br><br> This is due to the fact that all charges in a conductor reside on the outer surface, and always rearrange themselves to cancel out the electric field in the interior. 84 tag:techtv.mit.edu,:Array/186004140 2009-06-16 16:15:25 -0400 MIT Public Service Center Videos Sherife Abdel Messih '09 founded SPARK!, which is an innovative youth leadership program whose aim is to create an entrepreneurial ecosystem in Egypt. The program is comprised of a leadership camp for top notch high school students and an entrepreneurship camp for advanced college students. 116