Properties of electric field energy
1, the basic property of electric field energy: the charge moves in the electric field, and the electric field force should do work on the charge.
2. Potential φ
(1) Definition: the ratio of the potential energy Ep of a point charge in an electric field to the amount of charge.
(2) Definition formula: φ-unit: V symbol calculation.
(3) Features:
1, the potential is relative, relative to the reference point. But the difference of potential has nothing to do with the choice of reference point.
2. The potential is scalar, but it is signed. The symbol only indicates whether the potential at this point is higher or lower than the reference point.
3. The potential is determined by the electric field itself, and has nothing to do with Ep and Q. ..
4. The potential is numerically equal to the work done by the electric field force when the unit positive charge moves from this point to the zero potential point.
(4) the method of judging the potential level
1. Judging from the electric field line, the potential decreases along the electric field line. φA & gt； φB
2, according to the electric potential energy:
Positive charge: large potential energy and high potential; Small potential energy, low potential.
Negative charge: large potential energy and low potential; Small potential energy, high potential.
Conclusion: Only under the action of electric field force can electrostatic charge move from the place with high electric potential energy to the place with low electric potential energy.
2. Senior two physics compulsory one knowledge point induction notes two
Two kinds of problems in dynamics.
1, knowing the force of the object, find the motion of the object.
2. Given the motion of an object, find the force of the object (F force or a component force).
3. The general idea of applying Newton's second law to solve problems.
(1) defines the research object.
(2) Analyze the stress of the research object and draw a stress diagram.
(3) Establish a rectangular coordinate system, in which the initial velocity or direction of motion is positive, the same force as the positive direction is positive, and the force opposite to the positive direction is negative. The equations of Newton's second law are listed on the Y axis and the X axis respectively.
(4) When solving equations, all physical quantities should be unified in units, generally in international units.
4. Basic methods of analyzing two kinds of problems.
(1) Grasp the bridge between pressure and motion-acceleration.
(2) Analysis flow chart
3. Senior two physics compulsory one knowledge point induction notes three
alternating current
1. The uniform magnetic field has a coil, which rotates to generate alternating current. The variation law of current and voltage electromotive force is chord line.
Neutral surface timing is sine and parallel plane timing is cosine.
2.nbsω is a value, and the effective value is calculated by heat.
3. The transformer is used for AC, not constant current.
Ideal transformer, primary ui value, secondary ui value, equality is the principle.
The voltage ratio is proportional to the turns ratio; The current ratio is inversely proportional to the turns ratio.
Using the transformation ratio, if a certain number of turns is found, it can be converted into a turn ratio, which can be calculated conveniently.
Long-distance transmission, boost the voltage and reduce the current, otherwise the loss will be large and the user will step down.
4. Senior two physics compulsory one knowledge point induction notes four
1. Two kinds of charges, law of charge conservation and elementary charge: (e =1.60×10-19c); The charge of a charged body is equal to an integer multiple of elementary charge.
2. Coulomb's law: F=kQ 1Q2/r2 (in vacuum) {F: the force between point charges (n), k: the electrostatic constant k=9.0× 109N? M2/C2, Q 1, Q2: the electric quantity of two charges (c), R: the distance between two charges (m), the direction is on their connecting line, the acting force and reaction force repel each other, and the different charges attract each other.
3. Electric field intensity: E=F/q (definition formula, calculation formula) {E: electric field intensity (N/C), which is a vector (electric field superposition principle), and q: the quantity of electric charge (c).
4. The electric field formed by the vacuum point (source) charge E=kQ/r2{r: the distance from the source charge to this position (m), Q: the electric quantity of the source charge}
5. The field strength of uniform electric field E = UAB/D {Voltage between two points in the field strength direction (V)UAB:AB and the distance between two points (M)}
6. Electric field force: F=qE{F: electric field force (n/c)}, q: electric quantity of charge affected by electric field force (c), e: electric field strength (N/C)}
7. Potential and potential difference: UAB =φa-φb, UAB = WAB/Q =-δ EAB/Q.
8. Work done by electric field force: WAB=qUAB=Eqd{WAB: Work done by electric field force when charged body goes from A to B (J), Q: Charged amount (C), UAB: potential difference (V) between points A and B in electric field (the work done by electric field force has nothing to do with the path), E: uniform electric field strength, and D: along the field strength direction.
9. Electric potential energy: ea = q φ a {ea: electric potential energy (j) of charged body at point A, q: electric quantity (c), φ a: potential at point A (v}.
10. Variation of electric potential energy δEAB = e B-EA {difference of electric potential energy when charged body moves from position A to position B in electric field}
1 1. The change of electric field force work and electric potential energy δ eab =-wab =-quab (the increment of electric potential energy is equal to the negative value of electric field force work)
12. capacitance C=Q/U (definition formula, calculation formula) {C: capacitance (f), q: electric quantity (c), u: voltage (potential difference between two plates) (v)}
13. The capacitance of parallel plate capacitor C=εS/4πkd(S: the area opposite to two plates, D: the vertical distance between two plates, ω: the dielectric constant).
14. acceleration of charged particles in electric field (VO = 0):w =δek Δ ek or qU=mVt2/2, Vt=(2qU/m) 1/2.
15. Deflection when charged particles enter a uniform electric field at a speed Vo in a direction perpendicular to the electric field (regardless of gravity)
Horizontal vertical electric field direction: uniform linear motion L=Vot (in parallel plates with equal heterogeneous charges: E=U/d)
Throwing motion is parallel to the direction of electric field: uniformly accelerating linear motion with zero initial velocity d=at2/2 and A = F/M = QE/M.
5. High school physics compulsory one knowledge point induction notes five
electric field line
1. electric field line: some curves drawn in the electric field in order to describe the electric field vividly. The density of the curve indicates the magnitude of the field strength, and the tangent direction of a point on the curve indicates the direction of the field strength.
2. Characteristics of electric field lines
(1) Local field strength with dense electric field lines and sparse electric field lines.
(2) The electric field line of electrostatic field starts from positive charge and ends at negative charge, and the electric field line of isolated positive charge (or negative charge) ends at infinity.
(3) The electric field lines will not intersect or be tangent.
(4) The electric field line is imaginary and does not exist in the actual electric field.
(5) The electric field line is not a closed curve, which is not necessarily related to the trajectory of charged particles in the electric field.
3. Electric field lines of several typical electric fields
Distribution of electric field lines in (1) positive and negative point charge electric field
Features:
① The closer to the point charge, the denser the electric field lines and the greater the field strength.
②e Make a spherical surface centered on point charge, and the electric field lines are perpendicular to the spherical surface everywhere. On this sphere, the field strength is equal everywhere and the direction is different.
(2) The electric field lines are distributed in the electric field formed by the same amount of different point charges.
Features:
① along the point charge connection line, the field strength first decreases and then increases.
② On the middle vertical plane (middle vertical line) of the two-point charge connection line, the field strength direction is the same and always perpendicular to the middle vertical plane (middle vertical line).
(3) On the vertical plane (vertical line), at the equal distance from the midpoint 0 of the two-point charge connection line, the field strength of each point is equal.
(3) Characteristics of electric field line distribution in the electric field formed by equal point charges:
(1) The field strength at the point o of the two-point charge connection line is 0.
② The electric field line near the midpoint of the two-point charge connection line is sparse, but the field strength is not zero.
③ The electric field line from the midpoint of the two-point charge connection line to infinity first becomes dense and then becomes sparse.
(4) Uniform electric field
Features:
(1) The field strength at the point o of the two-point charge connection line is 0.
② The electric field line near the midpoint of the two-point charge connection line is sparse, but the field strength is not zero.
③ The electric field line from the midpoint of the two-point charge connection line to infinity first becomes dense and then becomes sparse.
(5) Uniform electric field
Features:
① The uniform electric field is an electric field with the same size and direction, so the electric field lines of the uniform electric field are parallel, equidistant and straight lines in the same direction.
② The density of E electric field line reflects the magnitude of field strength, and the direction of electric field is parallel to the electric field line.
6. Senior two physics compulsory knowledge point induction notes 6
1, stress analysis:
According to the concept of force, starting from the environment (how many objects are contacted and in what field) and the state of motion, the routine is as follows:
(1) Determine the research object and isolate it;
(2) Draw gravity first, then elasticity and friction, then electricity and magnetism;
(3) Check the stress diagram to find out the applied object of the drawn force, and analyze whether the result can make the object in a moving state (static or accelerated), otherwise it is multi-force or leakage force;
(4) The resultant force or component force cannot be repeatedly listed as the force acting on the object.
2. Integration method and isolation method
(1) integration method: several objects are regarded as a whole, and when carrying out force analysis, only the forces exerted by the objects outside the whole are analyzed, and the interaction forces inside the whole are not considered.
(2) Isolation method: It is assumed that the analyzed object is isolated from the related object system, and only the acting force of objects other than the object is analyzed, regardless of the acting force of the object on other objects.
(3) Method selection
When the physical problem involved is the interaction between the whole and the outside world, the application of holistic analysis can make the problem simple and clear, regardless of the role of internal forces; When the physical problem involved is the interaction between objects, it is necessary to apply the isolation analysis method, then the internal force of the interaction in the original whole will become the external force of each independent object.