Chapter 8 Electric field
1. Three ways of generating electric charges:
1. Electrification by friction: (1) Positive point charge: a glass rod rubbed with loaded silk; (2) Negative charge: the charge of a rubber rod rubbed with fur; (3) Essence: electrons are transferred from one object to another
2. Electrification of contacts: (1) )Essence: The charge moves; from one object to another; (2) When two identical objects come into contact, the charge is divided equally (3) Charge neutralization: When equal amounts of different charges come into contact, the charges cancel each other out; other and appear to the outside world. Non-electricity, this phenomenon is called charge neutralization;
3. Charging by induction: moving the charge near an uncharged conductor can charge the conductor (1); Basic filler properties: Same as different typesof charges repel each other and different types of charges attract each other (2) Essence: movement of the charge of the conductor from one part to another (3) During electrification by induction, the end; of the conductor nearest to the charge is charged with different types of charges, and the far end is charged with the same type of charges
4. The basic properties of electric charge: It can attract the light and small objects;
2. The law of conservation of electric charge: electric charge can neither be created nor destroyed, it can only emerge from one object is transferred to another object, or from a part of an object to another part; during the transfer process, the total amount of charge remains unchanged.
3. Elementary charge: The charge carried by an electron is called elementary charge. The charge is represented by e 1. e=1.6×. 10-19c; 2. The charge carried by a proton is also equal to the elementary charge ; 3. The charge carried by any charged object is an integer multiple of the elementary charge;
4. Coulomb's law: The force of interaction between two stationary point charges in a vacuum is proportional to the product of the charges that they carry and inversely proportional to the square of the distance which separates them. The direction of the force is in their connection, this force enters. The charges are called Coulomb force. 1. Calculation formula: F=kQ1Q2/r2 (k=9.0×109N.m2/kg2) 2. Coulomb's law only applies to point charges (the volume of the charge can be ignored) 3 . Coulomb's force. is not universal gravitation;
5. Electric Field: Electric field is a substance that generates an electrostatic force between point charges 1. As long as there is a charge, there must be an electric field around charge 2 ; , The basic properties of the electric field: The electric field has a powerful effect on charges (stationary and mobile) which are placed there; this force is called electric field force 3. Electric field, magnetic field and gravitational field are; any kind of substance
6, Electric field intensity: The ratio between the electric field strength F experienced by a charge placed at a certain point in the electric field and its amount of charge Q is called l 'electric field intensity at this point; 1. Definition formula: E = F/q; E is the electric field intensity; F is the electric field strength q is the test charge 2. The electric field strength is a vector and the direction of the field; the force at a certain point of the electric field is the direction of the force of the electric field on the positive charge placed at this point (opposite to the direction of the force of the electric field on the negative charge) 3, this formula is applicable to all electric fields 4. The formula for the electric field intensity of the chpoint arge: E=kQ/r2
7. Superposition of electric fields: If there are several point charges in space at the same time, the intensity of the electric field at a certain point of the space is the vector of the electric field intensity of these point charges at that point and; Problem Solving Method: Create directed line segments representing the field strengths of these point charges at that point and use the parallelogram rule to find the total field strength;
8. . Electric Field Lines: Electric field lines are lines artificially assumed by people in order to vividly describe the characteristics of electric fields. 1. Electric field lines are not objectively existing lines. 2. The shape of electric field lines: Electric field lines start from. positive charges and end in negative charges; G:\Use sawdust tour observe electric field lines DAT (1) There is only one positive charge: the electric field line starts from the positive charge and ends at infinity. a negative charge: it starts at infinity and ends at the negative charge; (3) There are both positive and negative charges: it begins at Positive charges eventually transform into negative charges; electric field intensity: dense electric field lines mean strong electric field (high electric field intensity); sparse electric field lines mean weak electric field (low electric field intensity); The tangent direction of a point on the electric field line is the direction of the field strength at that point; 4. Characteristics of Electric Field Lines: 1. Electric field lines are not closed curves. 2. Electric field lines in the same electric field; do not cross ;
< p> 9. Uniform electric field: an electric field whose intensity and direction are the same everywhere; the electric field lines of a uniform electric field are parallel and uniformly distributed; of a uniform electric field are a group of equally spaced parallel lines; 2. Electricity between parallel plate capacitors is a uniform electric field10. Potential difference: When the charge moves from one point to another; in the electric field, the ratio between the WAB work done by the electric field strength and the quantity of charge q is called potential difference 1. Definition formula: UAB=WAB/q; the electric field has nothing to do with the path;
3. Potential difference is also called voltage, and the international unit is volt
11. Electric potential at a certain level; the point in the electric field is equal to the work done by the force of the chelectric amp when the unit positive charge moves from this point to the reference point (point of zero potential); 1. Electric potential is relative and related to zero selection; potential surface; 2. Electric potential is a scalar quantity and the unit is volt V; 3. The relationship between the electric potential difference and the electric potential: UAB = φA -φB 4. The electric potential decreases in the direction of; the electric field line; when the electric field strength is to work, then the electric potential difference between the two points is not zero, it is not an equipotential surface 4. The same charge has the same electric potential energy at any position ; on the same equipotential surface; reason: when the charge moves from one point to another, the electric field strength does not work, so the electric potential energy does not change 5. Electric field lines point talways from a high temperature location; potential at a low potential location; 6. How to draw equipotential surfaces: the distance between adjacent equipotential surfaces is equal;
12. The relationship between electric field intensity and potential difference: in a uniform electric field, the difference of potential between two points in the direction of the field intensity is equal to the product of the field intensity and the distance between the two points 1. Mathematical expression: U=Ed 2. The applicable conditions of this formula are following. this only applies to the uniform electric field. 3. d is the vertical line between two equipotential surfaces;Distance;
13. Capacitor: A device that stores electric charge (electric field energy). 1. Structure: Made up of two metallic conductors insulated from each other. 2. The most common capacitor: parallel plate capacitor;
p>14. Capacitance: the ratio of the charge Q carried by the capacitor to the potential difference U between the two plates of the capacitor represented by “C”. Definition formula: C=Q/U; 2. Capacitance is a physical quantity that indicates the ability of a capacitor to store charges; 3. International Unit: Farad, abbreviation: Farad, represented by F 4. The capacitance of a capacitor is an attribute of the capacitor and has nothing to do with it. do with Q and U;
15. Parallel The governing formula for plate capacitor: C=εs/4πkd (where d is the vertical distance between the two plates, also known as the plate spacing; k is the constant of electrostatic force, k=9.0×10 9N.m2/c2; ε is the dielectric medium Electric constant, the dielectric constant of air is the smallest s represents the facing area between the two plates ;) 1. When both plates of the capacitor are connected to the power supply, the differencee of potential between the two plates remains unchanged and is equal to the voltage of the power supply 2. When the capacitor is not connected When it is connected to the circuit, the amount of charge carried by ; both plates of the capacitor remain unchanged;
16. Acceleration of charged particles: 1. Conditions: The direction of movement of the charged particles is perpendicular to the direction of field intensity and gravity is ignored; Principle: Kinetic energy theorem: The work done by the electric field force is equal to the variation in kinetic energy: W=Uq=1/2mvt2-1/2mv02 3. Inference: When the initial speed is zero , Uq=1/; 2mvt2; 4. Increase the speed of charged particles The electric field is also called accelerating electric field
Nine chapters of constant current
1. Current: Directional movement electric charges form current. 1. Conditions for generatingcurrent: (1) Free charge 2. Current is a scalar quantity, but it has a direction: we stipulate that the direction; in which the positive charge moves is the direction of the current;
Note: Outside the power supply, current flows from the positive pole of the power supply to the negative pole inside power, current; circulates from the negative pole to the positive pole; 3. The size of the current: The ratio of the amount of charge Q passing through the cross section of the conductor to the time t taken to pass these charges is called current I; (1) Mathematical expression: I=Q/t; (2) International unit of current: Ampere A
(3) Common units: milliampere mA, microampere uA (4) 1A=103mA=106uA
2. Law of Ohm: The current in a conductor is directly proportional to the voltage U at both ends of the conductor, and inversely proportional to the resistance R of conductor 1. Definition: I=U; /R; 2. Corollaire: R=U/ I; 3. The international unit of resistance is the ohm, expressed in
1kΩ=103Ω, 1MΩ=106Ω 4. Volt-ampere characteristic curve:
3. Closed circuit: by It consists of a power supply, wires, electrical appliances and keys; 1. Electromotive force: The electromotive force of the power supply is equal to the electromotive force of the power supply. The voltage between the two poles when the circuit is connected; represented by E;
2. External circuit: The circuit external to the power supply is called external circuit, the resistance of the external circuit is called external; resistance ; represented by R; the tension at both ends is called external tension; 3. Internal circuit: the circuit inside the power supply is called internal resistance, and the resistance of the internal circuit is called internal resistance; at both ends is called internal tension; for example: the generator coil and the solution in the dry battery areinternal The resistance of the circuit is the internal resistance 4. The electromotive force of the power supply is equal to the sum of ; internal and external tensions;
E=Uinside+Uoutside; Uoutside=RI; E=(R+r)I< /p>
4. Ohm's law in closed circuit: The current in the closed circuit is directly proportional to the electromotive force of the power supply, and inversely proportional to the sum resistances of internal and external circuits 1. Mathematical expression: I=E/(R +r) 2. When the external circuit; is disconnected, the external resistance is infinite, and the electromotive force of the power supply is equal to the voltage across the circuit; which is the definition of the electromotive force of the power supply 3. When the external resistance is zero (short circuit), the internal resistance; is low and the current is large, will burn out the circuit;
5. Semiconductor: Conductivity is between the conductor and the insulator; the resistance of the semi-conductoructor decreases with increasing temperature; /p>
6: The resistance of the conductor It increases with increasing temperature. When the temperature drops to a certain value, the resistance disappears and becomes superconducting;
1, Magnetic field:
1. The basic properties of the magnetic field: The magnetic field has a magnetic force on the magnetic poles and the currents therein are placed
2. Magnets and currents can produce magnetic fields
3. The interaction between magnetic poles, between magnetic poles and currents, and between currents and currents occur through the magnetic field; ;
4. The direction of the magnetic field: the north pole of the small magnetic needle in the magnetic field. The direction of is the direction of the magnetic field at that point;
2. Magnetic induction lines: draw a curvee directed in the magnetic field, and the tangent direction of each point of these curves is the direction of the magnetic field at that point;
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1. The magnetic field lines are assumed lines artificially by people in order to describe the magnetic field
2. The magnetic field lines of a magnet run from the north pole to the south pole outside and from the south pole; at the north pole inland; 3. . Magnetic field lines are closed curves;
3. Ampere's rule:
1. The magnetic field lines of a straight wire under tension: Hold the wire energized with your right hand and let the wire be straight. The direction pointed by the thumb is consistent with the direction of the current, and the direction pointed by the four bent fingers is the surrounding direction of the magnetic field lines
2. The magnetic field lines of the ring current: let the four fingers of the right hand bent and the ring current Thes directions are consistent, and the direction indicated by the right thumb is the direction of the magnetic field lines on the center axis of the ring wire
3. The magnetic field of the spiral tube under tension: Hold the tube spiral with your right hand and leave the four edges curved The direction of the finger is consistent with the direction of the ring wire; fluent. The direction indicated by the thumb is the direction of the magnetic field lines inside the spiral tube;
4. The geomagnetic field: the magnetic field generated by the earth itself from the geomagnetic north; geographic south pole (geographic south pole) to the geomagnetic south pole (geographic north pole);
5. Magnetic induction intensity: Magnetic induction intensity is a physical quantity that describes the strength of the magnetic field. 1. Size. of the intensity of the magnetic induction: in the magnetic field, it is perpendicular to the directionof the magnetic field. When a current-carrying wire is supplied, the ratio of the ampere force F to the product of the current I and the length of the wire L. is called the intensity of the magnetic induction. B = F/IL 2. The direction of the intensity of the magnetic induction is the direction of the magnetic field at this point (the small magnetic needle placed at this point, the direction of the North Pole) 3. The international unit of magnetic induction intensity: Tesla T, 1T=1N/A.m
6. Ampere force: the strength of the magnetic field on the current; 1. Size: In a uniform magnetic field, when the current is on; If the wire is perpendicular to the magnetic field, the ampere F on the current is equal to the product of the intensity of the magnetic induction B, the current I and the length of the wire L. 2. The definition of F=BIL (applicable to uniform magnetic field). electric fields and short wires) 3. Direction of Ampere's force: Left hand rule: Hold out the left handche, place the thumb and the other four fingers vertical and in the same plane as the palm, put your hand in the magnetic field, let the magnetic field lines pass vertically through the palm of your hand, spread your four fingers apart and point them in the direction of the current, then the direction indicated by your thumb is the direction of the ampere force on the current carrying wire.
7. Magnets and current can produce magnetic fields;
8. Magnetic field has a powerful effect on current
9. Current also ; has a powerful effect on current; (1) Currents in the same direction produce gravity; (2) Currents in opposite directions produce repulsion; 10. Molecules Current hypothesis: All magnetic fields are generated by current; 11. Magnetic materials: Substances which can be strongly magnetized are called magnetic materials: (1) Magnetic materials doux: materials which demagnetize easily after magnetization; Example: soft silicon steel; Application: manufacturing of electromagnets, transformers; magnetic materials: materials that do not demagnetize easily after magnetization; Example: carbon steel, tungsten steel, manufacturing: permanent magnets;
12. The force exerted by a magnetic field on moving charges is called Lorentz force< /p>
1. The direction of the Lorentz force is determined by the left hand rule: open your left hand so that the thumb and the other four fingers are coplanar And vertically, put your left hand in the magnetic field, let the lines of magnetic field pass vertically through the palm of your hand, the four fingers are in the direction of movement of positive charges (opposite to the direction of movement of negative charges) and the direction indicated by the thumb is the direction of the forceof Lorentz;
(1) The Lorentz force F must be perpendicular to the plane determined by B and V.
(2) The Lorentz force only changes the direction of the speed but not its magnitude
(3) The Lorentz force never works.
2. The magnitude of the Lorentz force
(1) When v is parallel to B: F=0< /p>
(2) When v is perpendicular to B: F=qvB
, Resistance law: The resistance at both ends of the conductor is linked to the length, transverse cross-sectional area and material properties of the conductor.
R=pl/S (formula for determining resistance)
P is only related to the properties of the conductor material .
R is related to temperature.
2. Volt-ampere characteristic curve: a graph describing the relationship between voltage and current Image.
3 . Diode: unidirectional conductivity; the positive electrode is connected to the positive electrode of the power supply.
4. Characteristics of series connection: ①The total voltage is equal to the sum of the voltages of each part.
②The current is equal everywhere
③The total resistance is equal to the sum of the resistances of all parts
④The total power is equal to the sum of the powers of each part
5. Parallel connection characteristics: ① The total voltage is equal to the voltage of each branch
②The total current is equal to the sum of the currents of each branch
③The reciprocal of the total resistance is equal to the sum of the reciprocal resistances of each branch
④The total power is equal to the sum of the powers of each branch.
6. Voltamp method: (1) Current limiting type (2) Voltage division type.
7. Methods for connecting equivalent schemes; : (1) Node bridging method; (2) Equipotential method (traction method).
8. Electromotive force: (1) Definition: The travail effected by the non-electrostatic force on the charge and the transferred charge. charge The ratio of quantities.
(2) Physical meaning: reflects the ability of the energy source to provide electrical energy.
(3) Formula: E force electromotive = W its/ q
(4) The electromotive force is only related to the properties of the power supply.
(5) The electromotive force and internal resistance are indicators of the food properties. The greater the electromotive force, the better the internal resistance.
9. Ohm's law in closed circuit: E = U exterior + U interior
10. The external resistance is proportional to the voltage across the circuit.
11. Method of measuring electromotive force and internal resistance of power supply: voltammetry, case voltage method and case installation method.
12. Principles of external and internal connections: observe which of the effectsof partial pressure and current division is the most obvious.
Formulas for external and internal connections: Small outside is too small, large inside is too big.
13 . When the meter head is changed to a voltmeter, a large resistor should be connected in series
When the meter head is changed to an ammeter, a small resistor should be connected in parallel< /p>
14. Multipurpose Electric Meter → Ohm's Law in Closed Circuit → Mark the Ohmmeter Scale
15. Power
16. Pure Resistance Circuit: A circuit in in which all electrical energy is converted into thermal energy.
17. The total power of the electrical supply: EI=IU outside + IU inside
18. AND gate circuit, OR gate circuit, and NOT the gate circuit (I only understand it)
19. Electrical black box problem (I also know it)
20. I=Q/t=nqvS……………………S referredence to the cross section through which the load passes; V refers to the speed of directional movement of the load
Let me give you a jingle. There is a power supply. The power force pushes the charge towards the positive pole. There is voltage between the positive and negative poles. When the circuit is turned on, the load moves in the equivalent diagram. of the DC circuit, the wire without resistance is reduced a little, and the equipotential points are connected to form a line; unnecessary wires in the open circuit are removed, and the nodes are connected in sequence; Organize and standardize graphics; and read it again at the end. Use Ampere's rule to judge the magnetic lines of force around the wire. To judge straight lines, use Rule 1. Let your right hand hold the straight thread straight. thumb and four fingers. These are magnetic lines. Use Rule 2 to determine the spiral. Stand firmhold the solenoid with your right hand. The direction of current is indicated on the four fingers and the N pole is at the tip of the thumb. There is a magnetic field around the magnet, and the N pole is forced to determine the direction; there is a magnetic field around the current, Ampere's rule determines the BIL Ampere direction, please pay attention to the perpendicular to each other. force Force ampere, remember to rotate the force to the left. The electromagnetic induction magnet generates electricity (electromotive force), produces a conditional magnetic flux and the loop is closed with current. Disconnecting the loop is the power supply, the. the induced electromotive force is large or small, the magnetic flux changes quickly or slowly, Lenz's law determines the direction, and resistance to change is the key. The conductor cuts the magnetic lines of force, and the right-hand ruler is more convenient.The uniform magnetic field coil (middle) rotates, the rotation produces alternating current, current, voltage and electromotive force. The changing pattern is a string, the neutral plane timing is sinusoidal, the parallel plane timing is cosine, NBSω is the maximum value and the effective value. The value is calculated using heat. Self-illumination is a light source, and the same type of uniform linear transmission if an obstacle is encountered, the propagation path needs to be changed. Among the two laws of reflection and refraction, the law of refraction is. The key. The optical medium has a refractive index, which is defined as a sine (ratio). Velocity ratio can also be used, just like wavelength ratio, to keep in mind that the incident light is optically dense. The angle of incidence is greater than the critical angle and the refracted light cannot be found. The object ist to infinity and the image is in focus. If you are chasing an object thousands of miles away, there is hope for an object that. is fast and slow. If you catch it at twice the focal length, the image will be Look at it at the same distance when you catch up to twice the focal length, the image runs faster than the object when you catch up; at twice the focal length, the object appears out of focus; when you catch up to twice the focal length, the object appears to look back, good things take a long time: metal can generate electricity when you look. exposed to light, and there is a limit to incident light. The kinetic energy of photoelectrons is large or small, which is related to the frequency of the photons. The number of photoelectrons is large or small, and it is closely related to the intensity. of light. The photoelectric effect can occur instantly and the frequency limitates depends on the function. Tips for analyzing circuits. the path to the end must be serial; if there are branches, it is in parallel. Counter A is equivalent to one wire; if it turns out to be in parallel, it's really miserable. to destroy the meter and the source. If an electrical device is connected through it, a local short circuit occurs. The V meter can and cannot be connected in series when connected, it means the circuit is broken. it is connected in series, the current is zero, this should be taken as obvious. Connect the circuit instructions What to do with the circuit: Series connection is very simple, each component is connected in sequence, it's a bit; difficult, just connect the main circuit and mark the necessary nodes; connect them all, then check again. How to connect the electric meter: A meter is connected in series; the V counter is connected to theux ends carefully. The positive (input) and negative (output) terminals cannot be reversed. Remember the measuring range; carefully cut the size.