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demhaha
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I made a capacitor following the instructions on this site http://www.instructables.com/id/Make-A-Water-Bottle-Capacitor/
Does anyone know how it works?
Does anyone know how it works?
SpectraCat said:What do you mean? It's a capacitor ... you have two conductors separated by a dielectric.
If you mean why does it have such a high capacitance, that is because the dielectric medium chosen for this capacitor includes an electrolyte (the total dielectric is the salt-water plus the thin plastic wall of the bottle ... the plastic is important to avoid electrochemical reactions). Some of the ions in the solution will migrate to the oppositely charged electrode and form a double layer. This is analogous to the polarization effect in a normal dielectric, but MUCH more effective at shielding the charge, so much higher charge densities can be achieved. In fact, you should be able to increase the capacitance (at least up to a point), by increasing the concentration of the electrolyte. This is because as the concentration goes up, the Debye screening length drops, allowing higher charge densities to be stabilized at a given voltage.
willem2 said:1.8 nF isn't a lot of capacitance for something as big as a water bottle. I think the salt water just works as a conductor and forms one of the plates.
A polyethylene capacitor of 10cmx10cm area and 0.1 mm thickness gives a capacitance
of [itex] \epsilon_0 \epsilon_r A/d [/itex] = 8.9 * 10^(-12) * 2.2 * 0.01 / 10^(-4) = 1.9 nF
nasu said:I also think that the main function of the salt water here is to act like a conductor rather than dielectric. It's just a simple way to put an electrode on the inside of the plastic bottle. An alternative, usually described in school experiment books, would be to fill the bottle with small pieces of aluminum foil and squeeze them inside until they form a compact block so the contact area with the wall is large enough.
For a "Leyda" bottle from PET (DC dielectric constant 2.6) with 0.5 mm wall I've got around 1nF. (dimensions used: 5 cm diameter, 14 cm height).
SpectraCat said:Well ... salt water really isn't a good conductor of electrons, although it is an excellent ion conductor. Since it doesn't conduct electrons, when you put a voltage across it, it acts like a dielectric with an EXTREMELY high polarizability (due to the high mobility of the solvated ions). Thus I think my description captured the essence of the mechanism.
willem2 said:Even if the salt water would make a capacitor, it will be in series with a capacitor with the bottle as dielictric.
What the polarizability of the water is, is unimportant, because you can't do better than the capacitance of just the bottle with two sides of it made of metal.
SpectraCat said:Well ... salt water really isn't a good conductor of electrons, although it is an excellent ion conductor. Since it doesn't conduct electrons, when you put a voltage across it, it acts like a dielectric with an EXTREMELY high polarizability (due to the high mobility of the solvated ions). Thus I think my description captured the essence of the mechanism.
A salt water capacitor works by using the conductivity of salt water to store electrical charge. The capacitor is made up of two conductive plates separated by a layer of salt water. When a voltage is applied to the capacitor, the salt water acts as an electrolyte, allowing charge to flow between the plates and creating a potential difference.
Salt water is used in a capacitor because it is a good conductor of electricity. This allows for a higher capacitance, or storage capacity, compared to other dielectric materials.
The capacitance of a salt water capacitor is higher than that of air or vacuum capacitors, but lower than that of ceramic or electrolytic capacitors. This is because salt water has a higher dielectric constant than air, but lower than other materials used in capacitors.
Yes, a salt water capacitor can be used for high voltage applications. However, it is not as commonly used as other types of capacitors due to the corrosive nature of salt water, which can damage the plates and decrease the lifespan of the capacitor.
Yes, there are safety concerns when using a salt water capacitor. Salt water is conductive and can cause electric shock if not handled properly. Additionally, the corrosive nature of salt water may also pose a risk if the capacitor leaks or breaks. It is important to handle and store salt water capacitors carefully and to follow proper safety precautions.