electric field intensity It is used to indicate the strength and direction of the electric field physical quantity 。 The ratio of the electrostatic force received by a charge placed at a point in the electric field to its charge is called the electric field strength of the point. Common E express. The strength of the electric field depends on the electric field itself, or the charge that excites the electric field, and has nothing to do with the forced charge in the electric field. The electric field intensity near the earth's surface is about 100V/m. [3]
The electric field strength is the electrostatic force received by the charge placed at a point in the electric field F With it Charge quantity Ratio, definition formula E = F / q , applicable to all electric fields; among F Is the electric field pair Tentative charge Force, q Is the charge amount of the test charge. Experiments show that at the same point of the electric field, Electric field force The ratio between the size of and the amount of the trial charge is constant, independent of the amount of the trial charge. It is only related to the charge generating the electric field and the specific position of the probe charge in the electric field, that is, the ratio reflects the characteristics of the electric field itself, so we use this ratio To represent the electric field strength field strength , usually used E express. The strength of electric field can be determined by Tentative charge The ratio between the force and the charge charge of the test point is determined. The probe point charge should meet two conditions; (1) Its dimension Must be small enough to be considered Point charge To determine the properties of each point in the field; (2) Its Electricity It should be small enough to prevent the original electric field The redistribution of or the effect on the active electric field is negligible. The direction of field strength at a point in the electric field is specified as positive charge Direction of electrostatic force received. [2] Niu (ton) per coulomb International System of Units The symbol is N/C. If the charge of 1C is subjected to Electrostatic force It is 1N, and the electric field strength at this point is 1N/C. The other unit of electric field intensity is volt (t) per meter, the symbol is V/m, which is equal to cattle/warehouse, that is, 1V/m=1N/C. It is a physical quantity that describes the nature of the force of the electric field. The electric field strength at a certain point in the electric field is numerically equal to the electric field force applied to the unit charge at that point.
The field strength is a vector whose direction is the direction of force applied to the positive test charge, and its magnitude is equal to the force applied to the unit test charge. The spatial distribution of field strength can be used Electric field line Image map. The strength of electric field is related to all parts of electrical equipment Insulating material Tolerance Conductive material Appears in current density The voltage on the terminal and whether it is generated corona 、 Flashover phenomenon It is one of the important physical quantities to be considered in the design. Principle of field strength superposition
Electric field strength compliance Principle of field strength superposition That is, the total field strength in space is equal to the vector sum of the field strength when each electric field exists alone. That is, the principle of field strength superposition is an experimental law, which indicates that each electric field is acting independently and is not affected by the presence of other electric fields. The above description is applicable to electrostatic field Also applicable to Rotating electric field Or a general electric field consisting of both. The superposition of electric field intensity follows the vector composition Parallelogram rule 。 The superposition principle of electric field strength is of great significance in solving practical problems, such as the application in electromagnetics, electronic engineering and other fields. By applying the superposition principle, it is more convenient to analyze and calculate the electric field, which provides an important theoretical basis for the research and application of related fields. The electric field between a pair of parallel plate electrodes has the same electric field intensity at each point. This electric field is called Uniform electric field (If the size of the plates is much larger than the distance between the plates, the non-uniform part of the electric field at the edge of the plates may not be considered). For the electric field around a charged sphere, the electric field intensity of each point is different. This electric field is called non-uniform electric field. Various field strength formulas
1. Applicable in any electric field Definitional expression ： E = F / q ， F Is the electric field pair Tentative charge Force, q Is put into a point in the electric field Test charge (trial charge) the amount of charge. Applicable conditions: applicable to all electric fields. 2. Point charge field strength formula in vacuum: E = kQ / r two among E Is the electric field strength, k yes electrostatic force constant ， Q Is the power of the source charge, r Is the distance between the source charge and the probe charge. [3] three Uniform electric field Field strength formula: E = U / d （ d Is the distance between two points along the direction of field strength) 4. Electric field of uniformly charged spherical shell: E within =0， E Outside = kQ / r two
5. Electric field intensity of infinite straight line: E =2 k ρ / r （ ρ Is an electric charge Linear density ， r For and Linear distance ） 6. Electric field intensity of charged half circle to center: E=2 k ρ / R （ ρ Is the linear density of charge, R Is the semicircle radius)
7. The radius is R The plane where the ring is located is vertical and the field strength on the central axis passing through the axis: kQh /( h two + R two ) 3/2
8. Field strength formula for any electrification curve: E =∫ k ρ / r two d s ....（ r Is the distance from the curve, is a function of coordinates x, y, ρ Is the linear density of charge) [3]
electric field electrostatic field or Coulomb electric field yes Irrotational field , Scalar can be introduced potential φ , while the relationship between the electric field intensity vector and the potential scalar is negative gradient Relationship. 
