tag:techtv.mit.edu,:Array/226549440 2008-07-18 11:31:42 -0400 MIT Department of Physics Technical Services Group <p>A 100 uF oil-filled capacitor is charged to 3 KV. This takes approximately 15 minutes, creating a charge on the capacitor that could be lethal. The capacitor is then discharged through a 12" length of 30 gauge bare iron wire.</p><p>When the high voltage current flows though high resistance wire, the bonds between iron molecules are shattered, resulting in a loud bang, a shower of sparks, and a cascade of wispy filaments floating through the air.</p><p>Not all of the charge on the capacitor is disharged through the wire, so a shorting bar must be used to release the remaining charge. </p> 121 tag:techtv.mit.edu,:Array/226528120 2009-02-20 09:52:36 -0500 MIT Department of Physics Technical Services Group First, an adjustable parallel-plate capacitor is held at a constant voltage. As the separation between the plates is widened, the electrometer shows charge (or current) flowing off of the plates, while the electroscope shows no change in voltage. Notice (by the deflection of the needle) that more charge flows off of the plates when they are closer together, and less when further apart. When the plates are brought back together, we see charge flowing back onto of the plates. <br><br> Next, we deposit a fixed amount of charge onto the left plate. Now, when the separation is widened, the electroscope shows a rising voltage, even as the amount of charge stays constant. When a block of plexiglass (a dielectric) is inserted between the plates, the voltage drops. However, when the plexi is removed, the voltage rises back up again, showing that the charge is still there. <br><br> This is one of the main reasons capacitors are built with dielectrics between their plates; more charge can be stored at a lower voltage. 126