Physics Demo Number: 038 |
Approximate Run Time: 10 min |
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Exploding Wire for Showing Plasma State of Matter with Help of Capacitor Stored Energy |
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Demo DescriptionA voltage doubler circuit charges a capacitor to around 330volts D.C. Then a solenoid slaps two big contact points together, dumping the energy in the capacitor onto a tiny wire as a load. The wire vaporizes almost instantly and the resulting plasma acts briefly as a current carrier. The net result is a very loud explosive noise ( like a high powered revolver going off ) and an intense flash of light (like looking at the sun). |
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Scientific Principles
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Equipment
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Equipment Location
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InstructionsThe dedicated apparatus is housed in the plastic box shown in the picture to try to make it safe for use. When the power cord is plugged into the 120V house
outlet and the toggle switch on the right end of the box thrown
to Charge position, a voltage doubler circuit charges the blue
can capacitor to around 330volts DC.
One scrapes the enamel off a strip of the #32 wire and wraps it tightly around each side of the bluish double banana plug . This bluish plug is then placed on the red banana plug which permanently resides on the plastic box. The second photo shows the left top end of the first photo from the back side. The point is that the Lucite rod near the middle left in the photo must be in the position shown to dump the capacitor into the wire instead of into the shorting resistor, which is activated by the Lucite rod for safety after the wire explosion. The third photo shows the front view of the Lucite rod safety switch, as well as the tethered supply of #32 wire, and the volmeter monitoring the voltage across the capacitor
Now when the toggle switch is flipped to fire position, a solenoid slaps two big contact points together and the energy in the capacitor is dumped onto the tiny wire as a load. Within about the first 15 microseconds the wire vaporizes, and the resulting plasma conducts energy from the capacitor for about 85 more microseconds. The result is a very loud explosive noise and a very intense light flash. The capacitor ends up with about 100V still across it. Thus about [(300-100) V] times [0.003 Farad] = [0.6 Coulomb] of charge flowed . Division by 100 microseconds gives an average current of 6000 amps. One must be very careful to make sure that the contact points end up in their open state , since then none of the residual capacitor voltage will appear across the terminals of the banana plug. Were one to grab hold of the two terminals (with the contact points closed) with both hands , the resulting discharge through the body could be LETHAL (even for only a few volts left on the capacitor). So for SAFETY pull the Lucite Bar Outwards to discharge any remaining voltage across the capacitor, after vaporizing the wire and before opening the contact points. Also be sure to push the Lucite Bar back in when initiating a new charging process. |
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Writeup created by David A. BurbaCopyright © 2013, Vanderbilt University. All Rights Reserved. |
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