The conductivities of several mediaunit in S/mMediaMediaConductivitiesConductivities46.17 ×107SilverSea water5.80×10710-3CopperPure water4.10×10710~5GoldDry soilTransformer3.54 ×10710-11Aluminumoil1.57×10710-12BrassGlass10710-15IronRubberu7
The conductivities of several media unit in S/m Media Conductivities Media Conductivities Silver Sea water Copper Pure water Gold Dry soil Aluminum Transformer oil Brass Glass Iron Rubber 7 6.17 107 5.80 10 3 10 − 7 4.10 10 5 10 − 7 3.54 10 11 10 − 7 1.57 10 12 10 − 7 10 15 10 − 4
The magnitude of the current density of the convection currentisnot proportional to the electric field intensity, and the direction maybe different from that of electric fieldintensityIf the charge densityis p, and the moving velocityis y, and thenJ=pvAs the polarization of dielectrics,the conducting properties of amedium can be homogeneous or inhomogeneous, linear or nonlinearand isotropic or anisotropic, with same meanings as before.The above equations are valid only fora linearisotropicmediumU
The magnitude of the current density of the convection current is not proportionalto the electric field intensity, and the direction may be different from that of electric field intensity. J = v As the polarization of dielectrics, the conducting properties of a medium can be homogeneous or inhomogeneous, linearor nonlinear, and isotropic or anisotropic, with same meanings as before. If the charge density is , and the moving velocity is v, and then The above equations are valid only for a linear isotropic medium
2.ElectromotiveForceWe first discuss the chemical action inside the impressed sourceunder open-circuitconditionIn theimpressed source,under theinfluenceofnon-electrostaticforcethepositivecharges will be moved continuouslytothepositiveelectrodeplateP,whilethenegative charges to the negative electrode7plate N.These charges on the plates produceanelectricfield E, with thedirectionpointedtoImpressed sourcethe plate N from the plateP, and theelectricfield Ewill be strongerwiththeincrease of the charges on the plates.uaV
E Conducting medium 2. Electromotive Force We first discuss the chemical action inside the impressed source under open-circuit condition. In the impressed source , under the influence of non-electrostatic force the positive charges will be moved continuously to the positive electrode plate P, while the negative charges to the negative electrode plate N. These charges on the plates produce an electric field E, with the direction pointed to the plate N from the plate P, and the electric field E will be stronger with the increase of the charges on the plates. P N E Impressed source E
The electric force caused by the charges on the plates will resistthe movement of the charges in the source. When the electric forceis equalto the non-electrostatic force,the charges are stopped, andthecharges onthe plateswill be constantSince the non-electrostatic force behaves as the force actingon the charge,the non-electrostatic forceis usually consideredas that produced by an impressedelectric fieldThis impressed electric field intensityis still defined as theforce acting on unit positive charge, but it is denoted as E
The electric force caused by the charges on the plates will resist the movement of the charges in the source. When the electric force is equal to the non-electrostatic force, the charges are stopped, and the charges on the plates will be constant. This impressed electric field intensity is still defined as the force acting on unit positive charge, but it is denoted as E'. Since the non-electrostatic force behaves as the force acting on the charge, the non-electrostatic force is usually considered as that produced by an impressed electric field
The impressed electric field E'pushes the positivecharges to thepositive electrode plate, and the negative charges to the negativeelectrodeplate,and the directionofis oppositetothat of the electricfield E produced by the charges on the plates.when the impressed electric field is equal but opposite to theelectric field produced by the charges on the plates, and the chargeswill beatrestIf the conducting medium is connected, the positive charges onthe positiveelectricplate will bemoved to the negativeelectricplatethrough the conducting medium, while the negative charges on thenegativeelectricplateto the positiveelectricplate.ln this way,thecharges on the plates will be decreased, and E < E'. The charges inthe sourcewill be moved again
The impressed electric field E' pushes the positive charges to the positive electrode plate, and the negative charges to the negative electrode plate, and the direction of is opposite to that of the electric field E produced by the charges on the plates. If the conducting medium is connected, the positive charges on the positive electric plate will be moved to the negative electric plate through the conducting medium, while the negative charges on the negative electric plate to the positive electric plate. In this way, the charges on the plates will be decreased, and E < E' . The charges in the source will be moved again. when the impressed electric field is equal but opposite to the electric field produced by the charges on the plates, and the charges will be at rest