1. concept: an object has the property of attracting light and small matter, that is, it is charged, or charged.

2, make the object charged method:

(1) triboelectrification: Two different substances rub against each other to make the object charged;

(2) Contact electrification: An uncharged object can be electrified when it comes into contact with a charged body.

Second, two kinds of accusations.

There are only two kinds of charges in nature:

(1) The charge brought by the friction between the wire and the glass rod is positive, which is represented by+;

(2) The charge caused by the friction between fur and rubber rod is negative.

Third, the interaction between charges.

1, like charges repel each other. 2. Heterogeneous charges attract each other.

Fourth, the method of testing whether the object is charged.

1, according to the nature of charged body and the interaction between charges.

2. Electroscope:

(1) Function: It is an instrument commonly used in laboratories to test whether an object is charged.

(2) Structure: metal ball, metal rod, metal foil and closed cover.

(3) Principle: Bimetallic foil, the same sex repels each other.

Verb (abbreviation of verb) charge amount

1, concept: the amount of charge is called the amount of charge, which is represented by the symbol q.

2. unit: the international unit is coulomb, which is referred to as library for short, and is represented by symbol C. ..

6. Explain the nuclear structure of electrical phenomena with electronic theory.

1. Concept: An atom is composed of a nucleus in the center and electrons running at high speed outside the nucleus. The radius of the nucleus is one hundred thousandth of the radius of the atom, and the nucleus concentrates almost all the mass of the atom and is positively charged.

2. Basic expenses:

(1) A library with an electronic charge of 1.6× 10- 19 is called a meta-charge, which is represented by the symbol E.

(2) Any charged body carries an integral multiple of e, so e can be used as the unit of charge.

3. Neutral state: Under normal circumstances, the positive charge of the nucleus = the negative charge of the electrons outside the nucleus, and the positive and negative charges cancel each other's external interactions, and objects made of atoms are also neutral.

4. Neutralization phenomenon: the phenomenon that equal amounts of heterogeneous charges meet and external interactions cancel each other out.

5, friction electrification:

(1) Reason: The nuclei of different substances have different abilities to bind electrons. When rubbing, the weak ones tend to lose positrons, while the strong ones gain negative electrons.

(2) Essence: It is the transfer of electrons (no charge is generated).

Seven, the current

1, concept: the directional movement of charge forms current.

2. Conditions for maintaining continuous current in the circuit:

(1) has a power supply; (2) the circuit is closed.

3. Current direction: the direction of positive charge directional movement is the direction of current. According to this regulation, the current starts from the positive pole of the power supply and flows to the negative pole of the power supply. It is the free electrons that actually move directionally in the metal conductor, and their movement direction is opposite to the specified current direction. In acid, alkali and brine solutions, positive and negative charges (ions) move in opposite directions.

Eight, power supply

1. power supply is a device that can provide continuous current.

2. From the point of view of energy, power supply is a device that converts other forms of energy into electrical energy.

3. The anode of dry battery is carbon rod (gathering positive charge) and the cathode is zinc skin (gathering negative charge).

4. Dry cells separate positive and negative charges through chemical reaction.

Nine, conductor, insulator

1. Objects that are easy to conduct electricity are called conductors, such as metal, graphite, human body, earth and aqueous solutions of acid, alkali and salt.

2. Objects that are not easy to conduct electricity are called insulators, such as rubber, glass, ceramics, plastics, oil and pure water.

3. The reason why the conductor is easy to conduct electricity: There are a lot of freely movable charges in the conductor.

4, the difference between conductor and insulator:

(1) depends on the amount and availability of free money;

(2) There is no strict boundary between them, and insulators can be transformed under certain conditions.

Circuit

1. circuit: a current path composed of power supply, electrical appliances, switches, wires and other components.

2. Electrical appliances: also called loads, are devices that use electric current to work and devices that convert electric energy into other forms of energy.

3. Conductor: The conductor connecting all circuit elements is the channel of current and can transmit electric energy.

4. Switch: Control the on-off of current.

5. Path: The circuit is closed and connected everywhere, and there is current in the circuit.

6. Open circuit: There is no current in the circuit due to the disconnection of a certain part of the circuit (all faults except opening and closing).

7. Short circuit: the phenomenon that the current directly returns to the power supply without going through the electrical appliance (equivalent to short circuit).

8. Hazard of short circuit: it will burn out the power supply, damage the circuit equipment and cause a fire.

XI。 circuit diagram

1. Circuit diagram: A diagram showing circuit connections with specific symbols.

2. Pay attention to drawing the circuit diagram: the components should be properly arranged and evenly distributed, and do not draw components in the corner. The whole circuit should be rectangular, angular and horizontal.

Twelve, series circuit

1. concept: connect circuit elements one by one.

2. Features:

(1) The current passing through one component also passes through another component, and there is only one path for the current;

(2) Any open circuit in the circuit cannot work, and only one switch is needed for control.

Thirteen, parallel circuit

1. Concept: connect circuit elements in parallel (there are only male terminals at both ends of parallel elements).

2. Features:

(1) The main current is divided into two (or more) branches in the branch;

(2) Each element can work independently without interfering with each other;

(3) The relay switch controls the whole circuit, and the branch switch only controls this branch.

Fourteen at present

1. Concept: The amount of charge passing through the conductor section in 1 s is called current, which is represented by symbol I. ..

2. Unit: The international unit of current is ampere, abbreviated as ampere, and represented by symbol A. ..

3. Expression: I=Q/t= library/second = ampere, that is, the amount of charge passing through the conductor section in one second is 1 library, and the current in the conductor is 1 ampere.

4. Other commonly used units: milliampere (mA) and microampere (μA).

5. Transformation relations: 1A = 103ma, 1ma = 103μ a,1a =106μ a.

6. Macro expression of current: For the same light bulb, the greater the brightness, the higher the temperature, that is, the greater the role of current, indicating the greater the current passing through the light bulb.

7. Instrument for measuring current, with identification symbol: ammeter on dial.

Fifteen, ammeter

1. How to read the current representation correctly: confirm the range of the ammeter you are using, and confirm the current value represented by each large battery and each small battery according to the range. The reading should be perpendicular to the surface.

2, the correct use of ammeter rules:

(1) ammeter must be connected in series in the circuit under test;

(2) Current must enter from the "+"terminal of ammeter and flow out from the "-"terminal;

(3) The measured current should not exceed the range of the ammeter. When the measured current cannot be estimated, the maximum range should be used first and touch should be attempted. Replace ammeter with small range or large range according to the situation.

(4) Never connect the ammeter to the two poles of the power supply without using electrical appliances.

Sixteen. voltage

1, concept: During the operation of the power supply, the positive electrode keeps accumulating positive charges and the negative electrode keeps accumulating negative charges, thus generating a voltage between the positive and negative electrodes of the power supply. The voltage is represented by the symbol u.

2. Voltage is the cause of current in the circuit, and power supply is the device that provides voltage.

3. Unit: The international unit of voltage is volt, which is denoted by the symbol V for short. ..

4. Other commonly used units: kilovolt (KV), millivolt (mV) and microvolt (μV).

5. Transformation relations: 1 kV = 1000 V, 1 V = 103,1MV =103 μ V.

6. Different currents will produce different voltages on the circuit.

7. Common voltage values: dry battery 1.5V, storage battery 2V, household electricity 220V, and safe voltage to human body is not more than 36V.

Seventeen, voltmeter

1, voltmeter is an instrument for measuring voltage.

2. Identify the symbol of voltmeter. V on the dial is a voltmeter.

3. How to read the voltmeter correctly (let two people check it on the ammeter, one vertical).

(1) Rules for proper use of voltmeter:

(1) voltmeter should be connected in parallel at both ends of the circuit under test;

(2) The current must enter from the "+"terminal of the voltmeter and from the "-"terminal;

(3) The measured voltage should not exceed the range of voltmeter. When the measured voltage cannot be estimated in advance, the maximum range should be used first and touch should be attempted. According to the situation, a voltmeter with small range or large range should be used;

④ The voltmeter can be directly connected to the positive and negative poles of the power supply, and the measured voltage is the power supply voltage.

Eighteen, the matters needing attention in the preparation of the experiment

1. Before the experiment, you must carefully read the textbooks and experimental books, complete the preview questions, and clarify the purpose and principle of the experiment.

2, enter the laboratory to strictly abide by the experimental discipline, according to the experimental group list on your marks, are not allowed to talk loudly. It is forbidden to take other complete sets of equipment. During the experiment, we should strictly observe the precautions and follow the experimental operation procedures and steps. Ask everyone to use their hands and brains, and raise their hands to report any questions.

3. Before connecting the circuit, you must draw the experimental circuit diagram and mark the instrument terminals "+"and "-".

4. When connecting the circuit according to the circuit diagram, the switch must be turned off. For complex circuits, series circuits should be connected first and then parallel circuits. The lead head should be tightened. The voltage of the student power supply must be set according to the requirements, and it can only be energized after inspection. If you are not sure, you should raise your hand and ask the teacher to check it for you.

The experiment must be carried out according to the planned steps, read carefully, record the data realistically, and fill in the experimental conclusion by analyzing the data.

6. After the experiment, check the equipment, arrange and recycle, and leave after being checked by the teacher.

Nineteen. Experimental conclusion

1, and the current intensity is equal everywhere in the series circuit: I = I 1 = I2.

2. The current of the main circuit in the parallel circuit is equal to the sum of the currents of each branch: I = I 1+I2.

3. The total voltage of series batteries is equal to the sum of the voltages of single batteries: U string = U 1 = U2.

4. The voltage of parallel battery pack is equal to the voltage of single battery: u and = U 1 = U2.

5. The total voltage of the series circuit is equal to the sum of the voltages at both ends of each part of the circuit: U = U 1+U2.

6. In parallel circuit, the voltages at both ends of each branch are equal, and the total voltage is equal to the voltages at both ends of each branch.

I. Resistance

1, concept: the resistance of a conductor to current is called resistance, which is represented by the letter R.

2. International unit: ohm, abbreviated as Europe, represented by the symbol ω.

3. Measurement method: If the voltage across the conductor is 1V and the current through it is 1Amp, the resistance of the conductor is 1Ohm.

4. Common units and conversion: kiloohms (kω), megaohms (mω),1mω =103kω =106ω.

Second, the factors that determine the magnitude of resistance

1 is related to the material of the conductor, which has different conductivity (silver, copper, aluminum, tungsten and iron).

2, related to the length of the conductor, the longer the conductor, the greater the resistance; Related to the cross-sectional area of the conductor, the smaller the cross-sectional area of the conductor, the greater the resistance, so the resistance of the conductor is determined by the nature of the conductor itself.

3. The resistance of conductor is also related to temperature, and the resistance of metal conductor increases with the increase of temperature.

4. Insulators can be transformed into conductors under certain conditions (temperature, humidity, etc.). ).

5. Comparing the resistances of different conductors can be obtained according to the similarities and differences of materials, lengths and cross-sectional areas.

Third, the type of resistance.

1, fixed value resistance: there is a fixed value to determine the resistance, the symbol in the circuit:

2, variable resistance:

The (1) resistance can be changed within a certain range as required.

(2) Type:

① Sliding rheostat, symbol in the circuit.

② Resistance box: The resistance can be changed by changing the length of series resistance wires in the circuit through several knob sliding arms, and the resistance value can be read directly.

Four, sliding rheostat

1, function: adjust the current and voltage in the circuit through the change of resistance.

2. Principle: Change the resistance value by changing the length of the resistance wire in the circuit.

3. Usage: As shown in the figure, there are four connections: ac, ad, bc and bd. The maximum resistance value and allowable current should be confirmed. Every time it is connected to the circuit, the resistance value should be adjusted to the maximum before use.

Five, ohm's law

1. When the resistance is constant, the current in the conductor is directly proportional to the voltage across the conductor: I ∝ u.

2. Under the condition of constant voltage, the current in the conductor is inversely proportional to the resistance of the conductor: I ∝1/r.

3. Law: The current in a conductor is directly proportional to the voltage across the conductor and inversely proportional to the resistance of the conductor.

4. Formula: I = u/r, all international units.

5, should pay attention to the problem:

The law (1) reflects the relationship between I, U and R of the same conductor;

(2) The same conductor can also refer to the total resistance of series and parallel circuits;

(3) u = i r is a measure of the voltage across the conductor;

(4) R = U/I is a measure of conductor resistance, which is determined by the conductor itself and has nothing to do with the size of U and I (it can be classified as ρ = M/V). For a conductor, the ratio of U to I is constant, that is, U∝I, which is also the principle of measuring resistance by voltammetry.

6, in the experiment should be paid attention to:

The resistance of (1) ammeter is very small, generally Ra < 0. 1ω, so it must be connected in series in the circuit of useful appliances.

(2) The resistance of the voltmeter is very large, generally RV > 3KΩ, so it must be connected in parallel at both ends of the tested electrical appliance (resistor) or power supply;

(3) When analyzing the circuit according to (1) and (2), the ammeter can be regarded as a straight line, and χ V can be regarded as an open circuit;

(4) The function of sliding rheostat in the circuit is to adjust the voltage at both ends of RX;

(5) When the circuit is connected, the switch should be turned off, and R should be placed in the position with the largest resistance. First, connect the series components to check whether it is correct, and then connect the voltmeter in parallel at both ends of RX.

Six, the characteristics of series circuit

1. The currents are equal everywhere in the circuit: I1= I2 = i3 = i;

2. The total voltage across the series circuit is equal to the sum of the voltages of all parts of the circuit: u = u1+U2+U3;

3. The total resistance of the series circuit is equal to the sum of the series resistances, and r = r 1+R2+R3. If n identical resistors r' are connected in series, r = n r', which is equivalent to the increase of conductor length when connected in series.

4. because I = U/R, I 1 = U 1/R 1, I2 = U2/R2, i3 = U3/R3, U/R = U 1 = U2/R2 = U3.

Seven, the characteristics of parallel circuit

1. The total current in the parallel circuit is equal to the sum of the currents in each branch.

2. The voltages at both ends of each branch in the parallel circuit are equal U = U 1 = U2 = U3.

3. The reciprocal of the total resistance of the parallel circuit is equal to the sum of the reciprocal of the parallel resistance,1/r =1/r1+1R2+1/R3. If n identical resistors are connected in parallel, then r = r'/n, n resistors.

4. Because U-I 1R 1-I2R2 = I3R3, when u is constant, I∝ 1/R, that is, in parallel circuit, each resistor has shunt function, and the shunt current of each branch is inversely proportional to the resistor. The greater the resistance, the smaller the shunt current.

5. Because P = U2/r, U2 = p1r1= p2r2 = p3r3, that is, when the voltage is constant, the power consumed by each resistor is inversely proportional to the resistor, and the larger the resistor, the smaller the power distributed.

Eight, electricity

1, the work done by current is called electric work, which is represented by the letter W. The process of doing work by current is the process of converting electric energy into other forms of energy (internal energy, light energy and mechanical energy), and the amount of electric energy is converted according to the amount of work done by current.

2. Calculation formula of electric power: W = UIT = I2RT = U2/R T, all in international units.

3. International electric power unit: Joule, 1 Joule = 1 volt-ampere-second.

4. Instrument for measuring electric power: electric energy meter, which can measure the electric energy consumed by electrical appliances.

5. Monthly fee (degrees) = reading at the end of the month-reading at the beginning of the month.

Nine, electricity

1. Concept: The work done by current in unit time is called electric power, and electric power is a physical quantity that describes the speed of work done by current.

2. Calculation formula: p = w/t = UIT/t = UI = I2r = U2/r, where all are international units.

3. International unit: Watt, abbreviated as Watt, represented by symbol W, 1 watt = 1 volt.

4. Other practical units: KW, horsepower, 1 kw =1000 w =1.36 horsepower,1horsepower = 735 watts.

5. From p = W=P t, another formula for calculating electricity P=W/t is W=P t, and if p = 1kW and t = 1h, then w = 1kWh.

6. Student experiment: Measure the power of light bulb. The circuit is similar to measuring resistance by voltammetry, except that Rx is replaced by light bulb.

X. rated power

1, and the voltage during normal operation of electrical appliances is called rated voltage.

2. The power of electrical appliances under rated voltage is called rated power.

3. Rated voltage and rated power can be used to calculate the normal working current and resistance value of electrical appliances.

4. The data given in the nameplate and instruction manual of electrical appliances are rated values.

5. The voltage actually applied when the electrical appliance is working is called the actual voltage.

6. The power of electrical appliances under actual voltage is called actual power: pReal = uReal ireal = i2realr = u2real/r.

7. Each electrical appliance has only one rated power, but there are many actual powers. The actual power varies with the voltage. The relationship between the actual value and the rated value is as follows:

(1) When U is a real number = U and P is a real number = P, the electrical appliance is in normal working condition;

(2) When the amount of U is less than that of U and the amount of P is less than that of P, the electrical appliance cannot work normally;

(3) When U is greater than U and P is greater than P, the service life of electrical appliances is shortened and it is easy to burn out.

XI。 Joule's law

1, Law: The heat generated by a current passing through a conductor is proportional to the square of the current, to the resistance of the conductor, and to the electrifying time. Formula: Q = I2RT (Joule).

2. The current does pass through the conductor. If all electric energy is converted into internal energy, W = Q = I2RT = UIT = (U2/R) T.

3. If I is constant in the series circuit, the greater R is, the more heat will be generated per unit time.

4. In parallel circuit, when U is constant, the smaller R is, the larger I is (I is the product of squares), and the more heat is generated per unit time. For example, the resistances of 220V, 100W and 25W lamps are 484Ω and1936Ω respectively. When connected in series, the 25W lamp emits more heat, and when connected in parallel, it is 100.

Twelve, electric heating

1. Electric heaters are devices that use electricity to heat, such as electric stoves, soldering irons, electric irons, rice cookers and electric ovens.

2. The main component of electric heater is heating element.

3. The heating element is made of resistance wire with high resistivity and high melting point wound on insulating material.

4. Advantages of electric heating: clean and sanitary, pollution-free, high thermal efficiency, and easy temperature control and adjustment.

Thirteen; , home circuit

1, household circuit composition: (in order) watt-hour meter, master switch, fuse box, socket, switch and electrical appliance.

2. Home circuit connection mode: lamps, electrical appliances and sockets are connected in parallel; The switch is connected in series with the lamp, and the fuse is connected in series with the live wire of the trunk line.

3, the main part of the household circuit:

(1) 220 volts to the ground is called the live line, and no voltage to the ground is called the zero line.

(2) Functions of the watt-hour meter: nameplate, maximum power and maximum current connection position.

(3) The function of fuse: When the current in the circuit increases beyond the allowable value of the circuit design, it can automatically cut off the circuit for protection.

(4) Material selection of fuse: high resistivity and low melting point (Al-Sb alloy).

(5) The socket is used for power supply of mobile appliances. For three hole socket, two holes are respectively connected with live wire and neutral wire, and the other hole is grounded.

(6) Pen: It is a tool for distinguishing live wire from zero wire, and consists of a metal nib, a resistor, a neon tube, a spring and a metal body at the end of the pen. When in use, the metal nib contacts the metal body of the pen tail, and the metal nib contacts the wire. For example, neon lights glow, and the surface is called fire line.

4. The reason of excessive current in household circuit:

(1) short circuit, the total resistance of the circuit is very small, and people stand on the ground and touch the fire line;

(2) The total power of electrical appliances is too large.

Fourteen Safe electricity

1, electric shock: the human body is a conductor. When the human body touches a charged body, there will be a current passing through the human body, which is called electric shock.

2. safe voltage: Practice has proved that the voltage below 36 volts is safe voltage.

3, low voltage (more than 36 volts) two forms of electric shock:

(1) Single-line electric shock, people standing on the ground touch the line of fire;

(2) Double-wire electric shock, the human body contacts the live wire and the zero line at the same time.

What needs special vigilance in life is that the originally insulated objects conduct electricity, and the objects that should not be charged are charged.

5, high voltage (10000 volts above) two forms of electric shock:

(1) high voltage arc shock;

(2) Step voltage gets an electric shock.

6. For safety, don't touch the low-voltage charged body, and don't get close to the high-voltage charged body.

7. Prevention in life: the insulation part is damaged, keep the insulation part dry, don't use wet manual switch, don't hang clothes on wires, and be careful not to touch the antenna when erecting TV antenna.

8. In order to use electricity safely, household appliances with metal shells must be grounded; Outdoor antennas on high buildings must have lightning protection devices.

9. When an electric shock accident occurs, cut off the power supply or unplug the insulated wire, so that the electric shock can be quickly separated from the power supply. When there is a fire, cut off the power supply first, and don't splash water with electricity to extinguish the fire.

Fifteen, simple magnetic phenomenon

1, magnets can attract ferromagnetic substances (iron, nickel, blunt) called magnetism, and magnetic substances called magnets.

2. The strongest part of a magnet is called a magnetic pole, and any magnet has only two magnetic poles.

3. Needle magnets can refer to north and south, one end of the guide rail is called South Pole or S Pole, and the north end is called North Pole or N Pole.

4. There is interaction between magnetic poles, the same name magnetic poles repel each other and the different names magnetic poles attract each other.

5, originally non-magnetic objects, the process of obtaining magnetism is called magnetization, and steel can be magnetized. 6. An object that easily loses its magnetism is called a soft magnet, and a magnet that does not easily lose its magnetism is called a hard magnet.

Sixteen, magnetic field

1. Concept: The space that exerts strong force on the magnet is called magnetic field. Magnetic field is a special substance, and there is a magnetic field in the space around the magnet.

2. Basic properties: It exerts a magnetic force on the magnets put in, and the interaction of the magnets is through the magnetic field.

3. Direction: At a certain point in the magnetic field, when the small magnetic needle is at rest, the direction of the force applied to the north pole or the tangent direction of a point on the magnetic induction line (along the flow direction of the magnetic induction line) is the magnetic field direction of that point.

4. geomagnetic field: the earth is a huge magnet, and there is a magnetic field around it, which is the geomagnetic field.

5. The N pole of the geomagnetic field is near the South Pole of the Earth, and its S pole is near the North Pole of the Earth.

Seventeen, magnetic induction line

1. Concept: Draw some curves around the magnet. The tangent direction of any point on the curve is consistent with the direction pointed by the north pole of the small magnetic needle. This direction curve is called magnetic induction line.

2. Function: It can directly describe the direction and intensity of each point in the magnetic field.

3. Flow direction of magnetic induction lines: The magnetic induction lines around the magnet all come out from the north pole of the magnet and return to the south pole of the magnet.

4. Be familiar with bar magnets, horseshoe magnets and the distribution of magnetic induction lines around them. (Read page 138)

Eighteen, the magnetic field of current

1, Oster experiment shows that there is a magnetic field around the wire and magnet.

2. The magnetic field passing through the outside of the solenoid is similar to that of a bar magnet.

3. Ampere's Law:

(1) Function: Determine the relationship between the polarity of the energized solenoid and the current direction.

(2) Method: Hold the solenoid with the right hand, so that the direction of current in the solenoid is four fingers, and the end pointed by the thumb is the north pole of the solenoid.

Nineteen, electromagnet

1. concept: the electrified solenoid is inserted into the magnetic core (soft magnet), that is, the electromagnet (solenoid is inserted into the magnetic core), and the magnetism is greatly enhanced.

2. Factors affecting the magnetic field strength of electromagnet:

(1) The electromagnet gets magnetized when it is energized and loses magnetism when it is de-energized;

(2) It is related to current, and the greater the current, the stronger the magnetism;

(3) When the current is constant, the more turns of solenoid coils with the same shape, the stronger the magnetism.

3. Application: electromagnetic crane, electric bell, electrode machine, generator, motor, automatic control.

Twenty, electromagnetic relay

1. Concept: The electromagnetic relay is essentially a switch controlled by an electromagnet.

2. Structure: electromagnet, armature, spring, moving contact and static contact.

3. Working principle: The switch in the low-voltage circuit is used to control the magnetism of electromagnet, so as to control the on-off of armature and static contact, and then control the working state of electrical appliances in the working circuit.

4. Application:

(1) Use low-voltage weak current to control strong current;

(2) remote operation;

(3) Automatic control.

Twenty-one, telephone

1, which basically consists of a microphone and a receiver.

2. Basic principle: Sound vibration is converted into changing current through the microphone, and then into vibrating sound through the receiver.

3. Microphone composition: metal box, carbon particles and diaphragm.

4. Working principle: speaking makes the carbon particles in the metal box of the microphone tight and loose → the resistance is large and small → the current in the circuit is weak and strong.

5. Headphone composition: permanent magnet, solenoid and thin iron sheet.

6. Working principle: The current whose intensity changes with the sound makes the magnetism of the electromagnet strong and weak, and the magnetism on the thin iron plate is big and small, which makes the thin iron plate vibrate and make the same sound as the speaker.

22, electromagnetic induction

1. Concept: A part of the conductor in the closed circuit cuts into the magnetic field and generates current in the moving conductor of the magnetic induction line. This phenomenon is called electromagnetic induction, and the generated current is called induced current. This phenomenon was discovered by the British physicist Faraday through experiments.

2. The direction of induced current: it is related to the direction of conductor movement and the direction of magnetic induction line.

3. Energy conversion: In electromagnetic induction, mechanical energy is converted into electrical energy.

Twenty-three, alternating current

1. Structure: rotor, stator, copper ring and brush.

2. Principle: electromagnetic induction. When the coil moves in a magnetic field under the action of external force, a periodically changing current, namely alternating current, is generated in the coil. A generator is a device that converts mechanical energy into electrical energy.

3. The cycle of using alternating current in our country's production and life is 0.02 seconds (the time of one cycle change).

4. The frequency is 50 Hz (the number of cycles per second), that is, 1 second has 50 cycles.

5. The direction of alternating current changes twice every cycle, that is, the direction of current changes within 1 second 100 times (alternating current is positive or negative).

Twenty-four, the role of magnetic field overcurrent

1. A charged conductor is subjected to a magnetic field in a magnetic field.

2. The stress direction is related to the current direction and the magnetic induction line direction.

3. The energized coil is forced to rotate to the equilibrium position in the magnetic field (the plane of the coil is perpendicular to the magnetic induction line) and stand still.

4. The forced motion of charged conductor in magnetic field is essentially the result of the interaction between magnetic field (permanent magnet) and magnetic field, and electric energy is converted into mechanical energy.

Twenty-five, DC cars

1. Structure: magnetic pole, coil, commutator and brush.

2. Principle: The electrified coil is stressed in a magnetic field.

3. Function of commutator: When the coil just turns to the balance position, the commutator can automatically change the direction of current in the coil, thus changing the direction of force on the coil and making the coil rotate continuously.

4. Advantages: convenient start and stop, simple structure, low price, less land occupation, high efficiency and no pollution.

5. Applications: trams, electric locomotives, planers, rolling mills, cranes, etc.

Twenty-six, electric energy

1, the superiority of electric energy:

(1) There are many sources of electric energy, and all kinds of energy can be easily converted into electric energy.

(2) electric energy is convenient for long-distance transmission;

(3) It is convenient to use and can be easily converted into other forms of energy;

(4) high efficiency and no pollution.

2. Conversion between electric energy and other forms of energy: hydropower is to convert water energy into electric energy; Thermal power generation is to convert chemical energy into electrical energy; Wind power generation is to convert wind energy into electric energy.