There are a lot offree electron, they havenegative chargeThere are many others who have lost their outer electronsPositive ion, they havepositive charge。Net charge refers to the charge carried by an object or part of it that is not offset.Isolated conductor with net charge, due to mutual repulsion of charges with the same sign, when the conductor reachesElectrostatic balanceThere is no net charge inside the conductor, and the net charge is only distributed on the surface of the conductor.[1]
The so-called "net charge" does not mean“electrostatic charge”。We know that there are a large number of free electrons in metal conductors, which have negative charges, and many positive ions that have lost their outer electrons, which have positive charges.These can be called "net charges".
But when the conductor is not charged, the positive and negative charges of the conductorCharge quantityIt is equal. We say that the conductor does not have a "net charge".When we make the charge amount of the positive and negative charges of the conductor unequal in some way, such as reducing the number of free electrons, the conductor will have excess positive charges. We say that the conductor has a positive "net charge", on the contrary, the conductor has a negative "net charge".It can be seen that the so-called "net charge" refers to the whole conductor or some part of the conductor（Electrostatic inductionThe difference between the amount of positive and negative charges.The net charge can only be distributed on the outer surface of the metal.
Repulsion and attraction of charge phenomenon
Net charge generation
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Sometimes we call the net charge the positive or negative charge of an object or part of an object that cannot be offset.
Apply voltage to a capacitor, and there will be a net charge on the electrode plate of the capacitor.When a dielectric is placed in an electric field, a net charge (bound charge) appears on the surface (or even inside) of the dielectric.
Net charge distribution
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The net charge can only be distributed on the surface of the conductor, but it is not evenly distributed on the surface.Both experiments and theories tell us that the charge density on the conductor surface is related to the curvature of the surface. The area density is large where the curvature is large, and the area density is small where the curvature is small.[2]
Electrostatic balance
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The charge distribution and electric field distribution in the conductor system are in a state that does not change with time, that is, the conductor is in a state where there is no macroscopic movement of the charge.The necessary condition for electrostatic balance is that the field strength at each point inside the conductor is zero.The conductor under electrostatic balance has the following properties:
(1) The conductor is equipotential, and its surface is equipotential;
(2) There is no net charge inside the conductor, and the charge can only be distributed on the surface of the conductor (when there is charge in the inner space of the conductor shell, the charge can be distributed on the inner surface of the conductor);
(3) The field strength direction of each point close to the conductor surface is perpendicular to the conductor surface.If the surface density of a point on the conductor surface is σ, the field strength value of a point immediately outside the surface E=σ/εzero。These properties can be determined byGauss theoremAnd proving the loop theorem of electrostatic field.The starting point of these two theorems is Coulomb's law, so they can also be said to be the inevitable result of the application of Coulomb's law to electrostatic balance.
It is worth noting that the electrostatic balance condition in which the field strength at each point inside the conductor is zero and there is no net charge inside the conductor is actually for uniform (including physical and chemical uniformity) conductors.For example, when the conductor is at uneven temperature, one end is maintained at ToneAnd the other end is maintained at TtwoAt the same time, it is in the state of no charge macro movement - electrostatic balance, which requires non-zero internal electric field force to balance the non electrostatic force (diffusion force of electron gas caused by temperature difference) generated by temperature difference.When two different metals contact, although there is no macroscopic movement of charge, there is charge at the interface, and there is potential difference between two conductors.In general, the necessary condition for electrostatic balance should be changed to zero of all resultant forces on the movable charge inside the conductor.[2]
