This learning activity draws an analogy between water in a “special” tank and current “flow” through a capacitor May students have a difficult time conceputualizing the AC current flow through a Capictor, especially when told that the current of the capicttor is an “insulator” and that the plates have no metal connection between them.This lession starts with a special tank of a particular volume, which is devided by An elastic membrance is sealed to wailes of the tank midway Between the ends around the circumfereance of the tank.The tank has tow pipe connections, one on each end (both sides of the membrance ). These pipes are labeled port A and poart B.
Let us assume a tank volume of 20 gallons. The membrane divides the volume in half with 10 gallons on each side. The tank is full of water the membrane is centered with no stretch. Pumping 5 gallons into part A displaces 5 gallons out part B. The memberance Streaches and stores eneregy.Plot thr volumes along a vertical line cetered at the membrance and time down the line.Pumping 5 gallons into poart A. The membarance returns to the center , non-strecthed position.Pumping another 5 gallons in to poart B displayes another 5 gallons out poart A. The memberance moves from moves from center, non center, non-stretched position to a position reveresed from the first position and again stores eneregy. Pumping 5 gallons into A displaces out poart B. The memberance returens to the center, non-streched position.It would apper that water flowed through the tank even through the poart A water never mixed with the poart B water. This operation can continue to be repeated many times. Tow thing must occur for this to happen.
Let us assume a tank volume of 20 gallons. The membrane divides the volume in half with 10 gallons on each side. The tank is full of water the membrane is centered with no stretch. Pumping 5 gallons into part A displaces 5 gallons out part B. The memberance Streaches and stores eneregy.Plot thr volumes along a vertical line cetered at the membrance and time down the line.Pumping 5 gallons into poart A. The membarance returns to the center , non-strecthed position.Pumping another 5 gallons in to poart B displayes another 5 gallons out poart A. The memberance moves from moves from center, non center, non-stretched position to a position reveresed from the first position and again stores eneregy. Pumping 5 gallons into A displaces out poart B. The memberance returens to the center, non-streched position.It would apper that water flowed through the tank even through the poart A water never mixed with the poart B water. This operation can continue to be repeated many times. Tow thing must occur for this to happen.
- The “flow” must be in one direction and then the other
- The volumes into either poart A or poart B cannot be so Large as to case the memberance to hit against either end of the tank.
If we do not reverse the flow and do not exced the volume of one side, we end up with the memberance strecthed to contain the volume toward the other side.This strecthed memberance exetrs a pressure to expel the volume and return to center position. If we exceed the volume, the memberanceis strecthed all the way to the opposite poart. If we contunue to force water in, the memberance will break and the water will punch through to the other side. This is “break down” of the memberance.
Let us now apply the sin-wave flow to the tank with a displacement volume that doesn’t exceed the tank half-side volume. Through the water never mixes in the tank, the tank appears to have no dividing memberance inside and the water flow in not affected.
The analogy
if we replaced the vo;ume of water with electrical charge (volume of electrons) and the memberance with an insulator,we have a capictor.The volume of one of the tank is analogous to the plate area and the distance between the plates.The memberance is analogius to the insulator and the strecth is analogous to the electric field’s effects on electrons in the insulator’s crystal lattice. Electrons flow into and out of the capictor just like the volume of water in the tank, this precisely how AC flowes “through” a capictor, it only appers to.The membrance is left displaced, there will be a residual pressure left.thi is analogous to the voltage, and the capictor is said to be charged (having a volume of electrone).Over fillng the tank causes the breakdown of the memberance. This is analogoues electrically to over changing a capictor and exceeding the voltage rating. Exceeding the voltage rating of the capictor may punch thriough the insulator just like the memberance.
Additonaly, if the memberance had very small holes in it, over the course of time lekage would occur from one side to the other , allowing the memberance to return toward the center, neutral, non-stretched position. This allows the pressure to equalize (discharge), just as the capictor’s electron charge bleeds off (discharges) due to leakage. The analogy still holds.
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