When the source charge Q/distance r from Q do not change, the inside of the box is the unchanged part: ke is called Coulomb's constant (we also call it the electrostatic force constant) This part inside the box is called the "electric field"

The electric field is the Coulomb force/electrostatic force/electric field force exerted by a unit (trial) charge.

Electric field and electric field strength are synonymous. The size of the electric field is the intensity of the electric field, and the electric field should be the dominant one. There is no such word in English as electric field strength

The electric field of a point charge is not equal everywhere. According to Coulomb's law, the formula conversion is as shown on the left Note: Which is the root? Which is the definition?

virtual electric field lines Marked with dots as charges, "electric field lines" are radiated. It should be noted that field lines are graphical illustrations of field strength and direction and do not represent actual physical meaning. But according to actual conditions, the number of these virtual electric field lines is indeed proportional to the amount of charge. Assume that the number of electric field lines is the number of charges! Electric field lines never intersect! Terminates at negative charge or at infinity. What is the relationship between electric field strength E and electric field lines?

1. Where the distance from the source charge is equal, the magnitude of the electric field is the same; 2. The denser the electric field lines, the greater the electric field; the sparser the electric field lines, the smaller the electric field; The density of the electric field lines is the intensity of the electric field.

Multiple electric fields at a certain point can be vectorially synthesized/each calculates its own spherical radius The curved electric field lines are the sum of all electric fields.

The electric field is the force exerted by a unit charge

The electric field is the force exerted by a unit charge, and any charge in the electric field Q will be affected by the force. Energy and force are directly related. If a force is applied, energy must exist there.

Electric potential energy of positive charge electric field

Electric potential energy of negative charge electric field

Point charge potential energy change

uniform electric field

Uniform electric field potential energy change

Useful Byproducts of Coulomb's Law

Electric potential energy is defined according to the work done by the electric field force, so the unit of electric potential energy is the same as the unit of work, Joule, symbol J

If an object is acted upon by a force, energy must be present there. Force is a gradient of energy.

A charge with a charge quantity of 1 C at this point The electric potential energy is 1 J, then the electric potential at this point is 1 V.

electric potential of point charge electric field

Electric potential of a uniform electric field

Blue: potential difference

It is usually specified that the electric potential energy at infinite distance is 0, or that the electric potential energy at the surface of the earth is 0. The zero point of electric potential is the same as the zero point of electric potential energy

1. Thick black lines with arrows: electric field lines - electric field force lines; the density of the line at a certain point is the size of the electric field, the size of the electric field force, and the density of the charge; The field lines do not cross. Along the direction of the electric field lines, the smaller the density of the lines, the smaller the electric field and the smaller the electric field force; 2. Color and depth represent electric potential energy: yellow represents zero electric potential energy. The darker the color, the greater the |electric potential energy|; the electric potential at 0 electric potential energy is 0; 3. The thin coil represents the equipotential surface; it is also the surface with equal electric potential energy. 4. The denser the electric field lines, the greater the electric field force, the more work done at the same distance, the greater the electric potential energy, and the denser the equipotential lines. 5. The electric field lines are perpendicular to the equipotential surface, and the electric potential gradually decreases along the direction of the electric field lines;

A stable and uniform electric field can be constructed through the amount of charge

electric field

In the SI International System of Units, the unit of capacitance is farad (farad), abbreviated as method, symbol: F. That is, when the capacitor carries a charge of 1 C, the potential difference between the two plates is 1 V, and the capacitance of the capacitor is 1 F. The F unit is very large, and the units commonly used in practice are mainly microfarads (μF) and picofarads (pF). 1 μF = 10^-6F 1 pF = 10^-12F

From the formula, it seems that the size of the capacitor is affected by the amount of charge and voltage, but it is not!

1. Left picture: If any conductor is added in the middle of the plate, the charge will flow and energy will be lost. So a dielectric is an insulator. 2. Dielectrics can be polarized by an applied electric field. Material polarization is similar to electrostatic induction (middle image). 3. Dielectric materials have no loosely bound or free electrons. When placed in an electric field, the charges in the dielectric do not flow out of the material, but only slightly deviate from their original average equilibrium position. (picture on the right)

Ceramic capacitors

Film capacitor

electrolytic capacitor

Tantalum capacitor

Different dielectrics have a huge impact on capacitance

Super capacitor

Above a certain electric field strength, the dielectric in the capacitor becomes conductive and loses its capacitive function. Thin The rated voltage marked on the product must be lower than the breakdown voltage.