|MadSci Network: Physics|
Hi Chelvam, That's an interesting question. In general, water is a better insulator than it is a conductor. This has to be qualified depending on the nature of the water. Pure distilled water with no minerals is a good insulator. Most tap water, fresh water from streams and rivers, and of course sea water all contain minerals in varying degrees. These minerals will increase the conductivity of the water, but it's far from a good conductor like copper or other metals. It's easier to answer the question of what happens when we immerse copper wire into an insulator. There are a number of mechanisms that cause electromagnetic and radio frequency interference. Let's consider each one in detail: 1. Near field magnetic interference. This type of interference is caused by lower frequency magnetic fields. Typically this is produced by transformers or high current carrying wires. The interference is called near field (or near zone) because the field strength drops off quickly as a function of distance. Insulators have little or no effect on magnetic fields, so there will be little, if any change in interference. Even still, magnetic interference can be significantly reduced by simply twisting a pair of conductors and minimizing the loop area. 2. Near field electric interference or capacitive coupling. This type of interference is caused by varying electric fields. This is often produced by varying voltages in a nearby conductor. The effect is small, but can be significant if high impedance amplifiers and small signals are involved. This is also a near field effect, so it also drops off quickly with distance. Insulators with a high permittivity will attenuate the electric field in proportion to the permittivity of the material. The relative permittivity of distilled water is quite high, around 80. This means that the electric field in the water will be 80 times smaller than the electric field outside the water. This is a big change, but it probably will not have a large effect on the over EMI/RFI if the wires are shielded and the shield is connected to the appropriate ground. Here's a link to a web page describing the effects of insulators in capacitors: http://www.allaboutcircuits.com/vol_1/chpt_13/3.html 3. Far field electromagnetic interference. This type of interference is caused by radio waves generated by an antenna or an unshielded wire carrying high frequencies currents. The electric field in this type of interference will also be attenuated like case #2. If you are talking about speaker wire, my guess is that you are interested in audio frequencies. The wavelength of these frequencies is very long, on the order of thousands of meters. For wires that are much shorter than this distance, there will be little effect. Of course, higher frequencies are a different story. Here's a link to a web site that describes the effect of microwaves in water: http://www.lsbu.ac.uk/water/microwave.html It is possible to shield against RFI, but this depends heavily on the frequency. In summary, the water will have little or no effect on EMI/RFI in most cases. If there is any effect, it will reduce the electric field component only. Any signal in the wire might will probably not be significantly affected. I hope that answers your question.
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