electrical knowledge of small science (about junior high school science of electricity knowledge what ah) 1. about junior high school science of electricity knowledge what ah
First, analyze the circuit: the circuit diagram is an important element of electricity.
Many electrical problems often begin with a sentence "as shown in the circuit" If the circuit diagram to identify the wrong circuit, the circuit of the current strength, voltage, resistance and other physical quantities of the calculation is also wrong, resulting in a "total loss" of the situation. So analyzing circuits is the first step in learning electricity.
Simple circuit diagrams can be analyzed by analyzing the path of the current through the circuit to judge. The fact that the current is always all the way through the circuit means that it is a series circuit.
If the current is separated by two or more paths in the circuit, it is a parallel circuit. For complex circuit diagrams, it is necessary to analyze the circuit by drawing an equivalent circuit diagram.
This method can be divided into four steps: 1. At the middle school level, it is generally assumed that the resistance of the ammeter is zero and the resistance of the voltmeter is infinite. Think of the ammeter as a wire and the voltmeter as an open circuit.
2, use letters to label the junction where the three wires intersect in the circuit diagram. 3, From the positive terminal of the power supply, draw a simple circuit diagram based on the path of the current and the position of each junction.
4. Reset the ammeter and voltmeter. Example 1: Draw the equivalent circuit diagram of the circuit shown in Figure 1 and explain the role of the ammeter and voltmeter.
Solution: (1), treat the ammeter as a wire and the voltmeter as an open circuit. (2) Mark the junction A, B, C, D of the circuit diagram.
(3) , according to the current path, the current starts from the positive pole of the power supply through the point D and R1 to the point A, the current is separated into two paths at the point A, all the way through the R2 to reach the point B, and the other way through the R3 to reach the point B, the two paths at the point B converge to reach the negative pole of the power supply to form a loop. Draw a simple and easy to see circuit diagram (Figure 1).
It can be seen that R2, R3 is connected in parallel, and then in series with R1. (4) , ammeter voltmeter reset.
From the circuit diagram I can be seen C, A two points connected together with a wire can be seen as the same point, the two terminals of the voltmeter are connected to point D and point A, so the voltmeter is to measure the voltage at both ends of R1. Current through the A point separated into two ways, all the way through the ammeter, and then through the R3 to reach the B point, so the ammeter is to measure the intensity of the current through the R3 (Figure 1.2).
By the above example, the importance of analyzing the circuit can be seen. In the review should particularly emphasize the need to analyze the circuit, draw equivalent circuit diagrams, so that students master this basic skill.
And can develop the encounter electrical problems, first draw a circuit diagram. Encounter circuit diagrams first analyze the circuit of good habits.
Second, the use of Ohm's law. Ohm's law is the core of middle school electrical calculations.
It reveals the relationship between the three most important physical quantities in electricity: current, voltage, and resistance. In the use of Ohm's law, special attention should be paid to: (1), to make clear that the law involves U, I, R.
Is the same part of the circuit of the three physical quantities. Never put the U, I, R does not belong to the same circuit in the formula.
(2) the formula , , , from the mathematical meaning alone is not fundamentally different. But the first two formulas are mathematical expressions of Ohm's law, the latter is the definition of resistance.
Can not be mistaken that "resistance is proportional to the voltage, with the current is inversely proportional to", and can not be considered "no voltage at the ends of the conductor, there is no resistance. Example 1: As shown in Figure 2, there are two resistors, series, the supply voltage of 6 volts, the resistance of the resistance of 10 ohms, the resistance of the voltage at the ends of 2 volts.
Requirements: the current through the resistor and the resistance of the resistor. Solution: By the characteristics of series circuits: .
This example is to emphasize the use of Ohm's law, U, I, R correspondence. Never use the voltage across the terminals or the supply voltage divided by the value of the resistance to find the current through, or the supply voltage divided by the current to find the value of the resistance.
Example 2: The circuit shown in Figure 3, the supply voltage is 6 volts, the resistance of resistor R1 is 15 ohms, the resistance of resistor R3 is 10 ohms, the ammeter reads 0.3 amps. What is the ohmic value of resistor R2? ANALYSIS: This is a mixed circuit with resistors R1 and R2 connected in parallel and then in series with R3.
To find the resistance of resistor R2, you must know the voltage across R2 and the current through R2. From the characteristics of series and parallel circuits, it can be seen that the voltage across resistors R1 and R2 is equal, and the sum of this voltage and the voltage across resistor R3 is equal to the supply voltage.
The sum of the currents through R1 and R2 is equal to the current in the dry circuit, which is the ammeter reading of 0.3 amps. SOLUTION: Voltage across R3: = 10 ohms * 0.3 amps = 3 volts Voltage across R1 and R2: = 6 volts - 3 volts = 3 volts Current through R1: Current through R2: 0.3 amps - 0.2 amps = 0.1 amps A. The resistance of resistor R2 is 30 ohms.
These two examples are relatively simple, the key is to emphasize the correspondence of U, I, R three physical quantities, as well as the characteristics of series-parallel circuits and the flexible use of Ohm's law. Third, the use of electric work, electric power, Joule's law formula.
Middle school students in the study of Ohm's law, but also think that electricity is not very difficult. Because only a formula or its deformation can solve the problem.
But learned electric power ( ), electric power ( ) and Joule's law ( ), for these three very close and closely linked concepts, easy to confuse. Some students reflected that this part of the content of the size of the formula add up to *** have more than a dozen, often use the wrong formula.
Learning good electricity, breakthrough in electricity, the key is to flexibly use the dozen formulas. In fact, these dozen formulas have a deep connection with each other, can be memorized through the following chart.
Purely resistive circuits (electric power definition) formula ,, commonly used in parallel circuits (voltage constant), formula ,, commonly used in series circuits (current constant). Equations and and only applies to pure resistance circuits, for non-pure resistance circuits can only use Joule's law to calculate the heat generated by the current.
Example 1: Two identical resistors, connect them in series to the power supply, the heat generated is Q. If they are connected in parallel to the same power supply, the heat generated in equal time is ( ) A, Q ; B, Q; C, 4Q; D, 2Q.
Analysis: From the question, we can see that the two are connected to the same power supply, the voltage is equal. It is more convenient to use the formula to carry out the calculation.
Let two identical resistors for R, the heat released after series connection is , the heat released after parallel connection is . By the ratio of the two formulas can be seen, the answer should be selected C.
Example 2: A, B, two lamps were labeled "4V, 2W" and "6V, 3W" of the word, the two lamps are connected in parallel in the circuit, which lamp is brighter? If two lamps are connected in series in a circuit, which lamp is brighter? (The applied voltage will not cause the filament to fuse.) Analysis: The brightness of a light bulb depends on its actual electrical power consumption, consumption.
2. Basic knowledge of electricity
Summary of knowledge of electricity I. Circuits The formation of electric current: the directional movement of charge to form an electric current. (Any directional movement of charge will form an electric current). Direction of current: from the positive pole of the power supply to the negative pole. Power supply: a device that provides a continuous current (or voltage). A power supply converts other forms of energy into electrical energy. For example, dry cell batteries convert chemical energy into electrical energy. Generators convert mechanical energy into electrical energy. Conditions for a continuous current: there must be a power source and the circuit must be closed. Conductors: Objects that conduct electricity easily are called conductors. For example: metal, human body, earth, salt water solution. Insulators: objects that do not readily conduct electricity are called insulators. Such as: glass, ceramics, plastic, oil, pure water, etc.. Circuit composition: by the power supply, wires, switches and appliances. Road has three states: (1) through: the circuit is called through; (2) open: the circuit is called open (sometimes called broken); (3) short circuit: directly connect the wires in the power supply poles of the circuit is called short circuit. Circuit diagram: the symbols used to represent the circuit connections is called a circuit diagram. Series connection: the components are connected one by one in sequence, called series connection. （Parallel: Connecting components in parallel is called a parallel connection. (Each branch is not affected by each other) Second, the current international unit: ampere (A); commonly used: milliampere (mA), microampere (A), 1 ampere = 1000 milliampere = 1,000,000 microampere. Measurement of current instrumentation is: ammeter, it is the use of rules: ① ammeter to be connected in series in the circuit; ② current from the "+" terminal into the "-" terminal; ③ measured current do not exceed the range of the ammeter; ④ is not allowed to not go through the electrical appliances and the ammeter is connected to the power supply on the poles. Commonly used in the laboratory ammeter has two ranges: ① 0 ~ 0.6 amps, the current value of each cell is 0.02 amps; ② 0 ~ 3 amps, the current value of each cell is 0.1 amps. Third, the voltage Voltage (U): voltage is the cause of the formation of current in the circuit, the power supply is to provide voltage devices. International units: volts (V); commonly used: kilovolts (KV), millivolts (mV). 1 kilovolt = 1000 volts = 1,000,000 millivolts. Measurement of voltage instrumentation is: voltmeter, the use of rules: ① voltmeter to be connected in parallel in the circuit; ② current from the "+" terminal into the "-" terminal; ③ the measured voltage does not exceed the range of the voltmeter; laboratory voltmeter has two ranges: ① 0 ~ 3 volts, the voltage value of 0.1 volts expressed in each cell; ② 0 ~ 15 volts, the voltage value of 0.5 volts expressed in each cell. Memorize the voltage value: ① 1 dry cell voltage 1.5 volts; ② 1 lead battery voltage is 2 volts; ③ home lighting voltage is 220 volts; ④ safety voltage is: no higher than 36 volts (some textbooks for 24 volts, but usually refers to the weather is not higher than 36 volts when the weather is sunny, not more than 12 volts on cloudy and rainy days); ⑤ industrial voltage of 380 volts. Resistance Resistance (R): indicates the resistance of a conductor to electric current. (The greater the resistance of a conductor to current, the greater the resistance, and the smaller the current through the conductor). International unit: ohm (Ω); commonly used: megohm (MΩ), kilohm (KΩ); 1 megohm = 1000 kilohm; 1 kilohm = 1000 ohm. Factors that determine the size of a resistor: material, length, cross-sectional area and temperature (R is independent of its U and I). Slide Resistor: Principle: Change the resistance by changing the length of the resistance wire in the circuit. Function: To change the current and voltage in a circuit by varying the resistance in the circuit. Nameplate: such as a sliding varistor labeled "50Ω 2A" means: the maximum resistance is 50Ω, the maximum current allowed to pass through the 2A. Correct use: a, should be used in series in the circuit; b, wiring should be "one on the next"; c, the resistance should be adjusted to the maximum place before the power supply. V, Ohm's law Ohm's law: the current in a conductor, and the voltage across the conductor is proportional to the resistance of the conductor is inversely proportional. Formula: the unit: I → ampere (A); U → volts (V); R → Europe (Ω). understanding of the formula: ① formula I, U and R must be in the same section of the circuit; ② I, U and R in any two known quantities can be another quantity; ③ calculations should be unified units. Application of Ohm's law: ① the same resistor resistance value is unchanged, independent of the current and voltage, its current increases with the increase in voltage. (R = U/I) ② when the voltage is constant, the larger the resistance, the smaller the current through. (I=U/R) ③ When the current is certain, the greater the resistance, the greater the voltage across the resistor. (U = IR) Resistors in series have the following characteristics: (refers to R1, R2 series, the more the series, the greater the resistance) ① current: I = I1 = I2 (the current in the series circuit is equal) ② voltage: U = U1 + U2 (the total voltage is equal to the sum of the voltages) ③ resistance: R = R1 + R2 (the total resistance is equal to the sum of the resistors) If n equivalent resistors are connected in series, there is a total R = nR ④ voltage divider: =; Calculation of U = U1 + R2 (total resistance is equal to the sum of the resistors) ⑤ voltage divider: =; Calculation of R = U1 + U2 (total resistance is equal to the sum of the resistors) ⑤ Proportionality: current: I1:I2=1:1 (Q is heat) The parallel connection of resistors has the following characteristics: (refers to the parallel connection of R1,R2, and the more parallel, the smaller the resistance) ① Current: I=I1+I2 (the dry circuit current is equal to the sum of the branch currents) ② Voltage: U=U1=U2 (the dry circuit voltage is equal to the voltage of the branch circuits) ③ Resistance: (the reciprocal of the total resistance is equal to the reciprocal of the resistance and) if n equal value resistance in parallel, there is R total = R ④ shunt effect:; calculate I1, I2 available:; ⑤ proportionality: voltage: U1: U2 = 1:1, (Q is the heat) six, electric power and electric power 1. electric power (W): the amount of electrical energy converted into other forms of energy is called electric power, 2. work of the international units: Joule. Commonly used: degrees (kWh), 1 degree = 1 kWh = 3.6 * 106 joules. 3. 3. Measurement of electrical work tools: energy meter 4. Electrical work formula: W = Pt = UIt (where the unit W → Jou (J); U → volts (V); I → ampere (A); t → seconds). The use of W = UIt calculations, note: ① formula W. U. I and t is in the same section of the circuit; ② calculations should be unified units; ③ known any of the three quantities can be found in the fourth quantity. There is also the formula: = I2Rt electric power (P): the current to do work faster or slower. International units: watts (W); commonly used: kilowatts Formula: formula in the unit P → watts (w); W → joule; t → seconds; U → volts (V), I → ampere (A) use of the units to be unified in the calculation, ① if the W with joule, t with the second, then the unit of P is watts; ② if the W with kilowatt-hours, t with the hour, then the unit of P is kilowatts. 10. Calculation of electric power can also be used in the right formula: P = I2R and P = U2 / R 11. Rated voltage (U0): the voltage of the normal operation of the appliance. Another: rated current 12. rated power (P0): the appliance in the amount.
3. Seek a knowledge of electricity
The word "electricity" in the West is from the Greek word amber transference, in China is from the thunder and lightning phenomenon. Since the middle of the 18th century, the study of electricity has flourished. Each of its major discoveries has led to extensive practical research, thus promoting the rapid development of science and technology.
Nowadays, no matter human life, scientific and technological activities, as well as material production activities have been inseparable from electricity. With the development of science and technology, some research content with specialized knowledge gradually independent, the formation of specialized disciplines, such as electronics, electrical engineering. Electricity can also be called electromagnetism, physics is quite important in the significance of the basic disciplines.
A brief history of the development of electricity
The records of electricity can be traced back to the 6th century BC. As early as 585 BC, the Greek philosopher Thales has recorded with a wooden block rubbed amber can attract broken grass and other light objects, and later found that the friction of the coal jade also has the ability to attract light objects. In the next 2,000 years, these phenomena are seen as the same as the magnet attracts iron, belong to the nature of the substance has, in addition to what other significant discoveries.
In China, at the end of the Western Han Dynasty, there has been "Threshing Turtle (tortoiseshell) suction Royale (the meaning of small objects)" records; Jin Dynasty, there is further on the friction caused by the phenomenon of electric discharge records "now combing hair, unzipped clothes, with the comb unraveling the knot of those who have the light, but also the sound of zha! ".
In 1600, the British physicist Gibb found that not only amber and coal jade friction can attract light objects, but also quite a lot of substances by friction also have the nature of attracting light objects, he noticed that these substances by friction and does not have the magnet that refers to the nature of the north and south. To indicate the difference from magnetism, he called this property "electric", using the Greek alphabet for amber. In the course of his experiments, Gibb made the first electrical checker, a thin metal rod fixed in the center that could be rotated to point at the rubbed amber when it was brought close to it.
The first friction starter was invented around 1660 by Gaelic of Madburg. He made a rotating sphere shaped like a globe out of sulfur, and he rubbed it with the palm of his dry hand to obtain electricity. Gaelic friction starter motor after continuous improvement, in the electrostatic experimental research plays an important role until the 19th century, Holtz and Tepler were invented respectively after the induction starter motor was replaced.
In the 18th century, the study of electricity developed rapidly. 1729, the British Gray in the study of amber electric effect can be transferred to other objects when the conductor and insulator found that the difference between: metal can be conductive, silk does not conduct electricity, and he first made the human body charged. Gray's experiments attracted the attention of Diffé in France, and in 1733 Diffé found that insulated metals could also be electrified by friction, so he concluded that all objects could be electrified by friction. He called the electricity generated on glass "glassy", and the electricity generated on amber was the same as that generated by resin, which was called "resiny". He got: objects with the same electricity repel each other; objects with different electricity attract each other.
In 1745, Musschenbroek of Leiden, the Netherlands, invented the Leiden bottle, which preserves electricity. The invention of the Leyden jar provided the conditions for the further study of electricity, and it played an important role in the spread of knowledge about electricity.
Almost at the same time, the United States of America, Franklin did a lot of meaningful work, so that people's understanding of electricity is richer. 1747 he put forward based on experiments: under normal conditions, electricity is an element that exists in a certain amount in all substances; electricity is the same as a fluid, friction can be made to transfer it from one object to another, but can not be created; the total amount of electricity in any isolated object is unchanged; this is commonly known as the law of conservation of charge. He called the excess of electricity gained by an object during friction positively charged, and the part of the object that loses electricity and is insufficiently charged negatively charged.
Strictly speaking, this one-fluid theory of electricity is not correct today, but the terms he used for positive and negative electricity are still used today, and he also observed that the tips of conductors are more easily discharged, among other things. As early as 1749 he noticed that lightning flashes had much in common with electrical discharges, and in 1752 he proved that lightning flashes were electrical discharges by conducting a lightning experiment by placing a kite in a cloud during a thunderstorm. The most fortunate thing about this experiment was that Franklin was not actually electrocuted, because it was a dangerous experiment, and later on someone was electrocuted when repeating the experiment. Franklin also suggested the use of lightning rods to protect buildings from lightning strikes, first realized in 1745 by Divis, which is probably the first practical application of electricity.
4. Knowledge of electricity
As far as more than 2500 years ago, the ancient Greeks found that the amber rubbed with fur can attract some like fluff, wheat straw and some other small things, they called this phenomenon "electricity".
In 1600 AD, the British doctor Gilbert (1544~1603) did many years of experiments, discovered the "electric power", "electric attraction" and many other phenomena, and was the first to use the "electric power", "electric attraction". "Electricity", "electric attraction" and other specialized terms, so many people call him the father of the study of electricity. In the 200 years after Gilbert, there are many people have done many experiments, and continue to accumulate knowledge of the phenomenon of electricity. 1734 Frenchman Duval found the same number of electricity mutual repulsion, different numbers of electricity mutual attraction phenomenon. 1745, Prussia (Germany's predecessor), a vice bishop Crest in the experiments found the phenomenon of electric discharge.
In the middle of the 18th century, across the ocean in the United States, the great electrician Franklin did many more experiments, further revealing the nature of electricity, and proposed the term current. He believed that electricity was a weightless fluid that existed in all objects. If an object receives more than its normal amount of electricity, it is said to be positively charged (or "positive"); if an object receives less than its normal amount of electricity, it is said to be negatively charged (or "negative"). Discharge is the process by which a positive current is converted into a negative one. Franklin's statement, at that time, can indeed explain some of the phenomena of electricity, but the understanding of the nature of electricity and our current "two objects rubbing each other, easy to move is exactly the negatively charged electrons," the view is the opposite.
Franklin's other major contribution to the science of electricity, is through the famous kite experiment in 1752, "capture the sky electricity", proving that the sky lightning and ground electricity is the same thing. He put a very large kite into the clouds with a metal wire. A piece of string was attached to the lower end of the wire, and a set of keys hung from the wire. Franklin pulled on the string with one hand and gently touched the keys with the other. He immediately felt a sharp shock (electric shock) and saw a small spark between his finger and the key. This experiment showed that the metal string of the rain-soaked kite became a conductor, drawing the charge from the lightning in the air between the finger and the key. This was a sensational event at the time. A year later Franklin made the world's first lightning rod.
The study of current phenomena, for people to study in-depth electricity and electromagnetic phenomena have important significance. The first to start the study of electric current is the Italian anatomy professor Giovanni (1737-1798). Giovanni's discovery originated from an extremely common lightning phenomenon in 1780. The lightning caused a spasm in the legs of a frog on a table in Giovanni's dissecting room, which was in contact with a ring of forceps and tweezers. His scientific rigor did not allow him to give up the study of this strange phenomenon of "chance". He spent 12 years studying the electrical action in the movement of muscles like the frog's leg. Finally, he found that if the nerves and muscles were brought into contact with two different metals (such as copper and iron wire), the frog's legs would spasm. This phenomenon was a phenomenon produced in a kind of electric current circuit. However, Giovanni was still unable to answer the question of the cause of this current phenomenon, and considered the spasm of the frog's legs to be a manifestation of "animal electricity", and that the circuit made up of metal wires was merely a discharge circuit.
Giovanni's view caused a huge reaction in the scientific community at that time, but another Italian scientist, Vodafone (1745-1827), disagreed with Giovanni's view, believing that electricity exists in the metal, not in the muscle, and the two distinctly different views caused the scientific community to debate and divide the scientific community into two major factions.
In the spring of 1800, there was a further breakthrough in the debate about the cause of electricity. Voltar invented the famous "Voltar battery". This battery was a device consisting of a series of round zinc and silver plates interlocked, with a cardboard plate soaked in salt water or other conductive solution separating each pair of silver and zinc plates. The silver and zinc sheets are two different metals, and the salt water or other conducting solution serves as the electrolyte, and they form the current circuit. This was a relatively primitive type of battery, a battery pack made up of many silver and zinc cells connected together. But at the time, it was not easy for Voltar to invent this battery.
The invention of the Voltar battery allowed people for the first time to obtain a continuous current that could be artificially controlled, which provided a material basis for the future study of the phenomenon of electric current, and also opened up the prospect of the application of the current effect, and soon became a powerful tool for electromagnetism and chemical research.
5. Junior high school physics on the knowledge of electricity
The structure of the knowledge of electricity points a, the object charged 1, the concept: the object has the nature of attracting light matter, that is, charged, or charged.
2, so that the object charged method: (1) friction electricity: two different substances rubbing each other, so that the object charged; (2) contact with electricity: the original uncharged objects and charged body contact can be charged. Second, two kinds of charge nature has only two kinds of charge: (1) silk and glass rod friction charge is positive with + said; (2) fur and rubber rod friction charge is negative with - said.
Third, the interaction between charges 1, the same kind of charge mutual exclusion. 2, dissimilar charges attract each other.
Fourth, test whether the object is charged 1, according to the nature of the charged body and the interaction between charges to determine. 2, the checker: (1) role: is a laboratory commonly used to test whether the object is charged instrument.
(2) structure: metal ball, metal rod, metal foil, closed cover. (3) Principle: bimetallic foil, same sex repulsion.
V. Charge 1, the concept: how much charge is called charge, expressed by the symbol Q. The charge is the amount of charge. 2, the unit: the international unit is the coulomb, referred to as Coulomb, with the symbol C said.
Six, the structure of the atomic nucleus with electron theory to explain the electrical phenomena 1, concept: the atom is located in the center of the nucleus and the nucleus of the high-speed operation of the electrons are composed of the radius of the nucleus of the atom is one hundred thousandth of the radius of the atom, the nucleus of the atom is almost concentrated all the mass of the atom, positively charged. 2, the basic charge: (1) an electron with a charge of 1.6 * 10-19 library, called the basic charge, expressed by the symbol e.
(2) The charge of any charged body is an integer multiple of e, so e can be used as a unit of charge. 3, neutral state: usually the nucleus of the atom with a positive charge = the negative charge of the electrons outside the nucleus, positive and negative charges cancel each other out, the external non-electrical, composed of atoms, the object is also neutral.
4, neutralization phenomenon: equal amount of dissimilar charges meet, the external role of the neutral phenomenon cancel each other. 5, the friction of electricity: (1) reason: the nuclei of different substances binding electrons of different capabilities, the friction of the weak capabilities of easy to lose electrons positively charged, strong capabilities to get electrons negatively charged.
(2) Substance: the transfer of electrons (did not create a charge). Seven, current 1, concept: the directional movement of charge to form a current.
2, to maintain a continuous current in the circuit conditions: (1) a power supply; (2) the circuit is closed. 3, the direction of the current: people stipulate that the direction of positive charge directional movement for the direction of the current, according to this provision, the current is from the positive pole of the power supply, flow to the negative pole of the power supply.
In the metal conductor is actually directed to move the free electrons, the direction of its movement and the direction of the current is opposite. In acids, bases, saline solutions, positive and negative charges (ions) move in opposite directions.
VIII, power supply 1, the power supply is able to provide a continuous current device. 2, from the energy point of view, the power supply is a device that converts other forms of energy into electrical energy.
3, the positive electrode of the dry cell is a carbon rod (gather positive charge), the negative electrode is zinc skin (gather negative charge). 4, dry cell is through the chemical reaction method to make positive and negative charge separation.
IX, conductors, insulators 1, easily conductive objects called conductors, such as metal, graphite, the human body, the earth and acids, bases, salts, such as aqueous solutions. 2, not easily conductive objects called insulators, such as rubber, glass, ceramics, plastics, oil, pure water and so on.
3, the conductor is easy to conduct electricity: there are a large number of free-moving charges in the conductor. 4, the difference between conductors and insulators: (1) lies in the number of free charge, presence or absence; (2) there is no strict boundary between the two, under certain conditions, insulators can be transformed.
X. Circuit 1, circuit: the power supply, appliances, switches, wires and other components of the current path. 2, electrical appliances: also called load, is the use of current to work on the device, is the conversion of electrical energy into other forms of energy.
3, wire: the conductor connecting the various circuit elements, is the channel of the current, can transport electrical energy. 4, switch: control the current off.
5, through: the circuit is closed, everywhere connected, there is current in the circuit. 6, open circuit: because the circuit is disconnected somewhere, and the circuit has no current (except the switch is a fault).
7, short-circuit: the current does not pass through the appliance and directly back to the power supply phenomenon (equivalent to circuit shortening). 8, the hazards of short-circuit: you can burn out the power supply, damage to circuit equipment causing fire.
XI, circuit diagrams 1, circuit diagrams: with the prescribed symbols to indicate the circuit connection diagram. 2, draw the circuit diagram should pay attention to: the location of the components should be arranged appropriately, the distribution should be uniform, the components should not be drawn in the corner, the whole circuit is best rectangular, angular, the circuit horizontal and vertical.
XII, series circuits 1, the concept: the circuit elements are connected one by one in turn. 2, features: (1) through a component of the current through another component, the current only a path; (2) any one of the circuit is open, the appliances can not work, so only a switch control.
XIII, parallel circuits 1, concept: the circuit elements connected in parallel (parallel components at both ends of the public **** end). 2, features: (1) dry circuit current in the branch, divided into two (or more) branches; (2) the components can work independently of each other; (3) dry switch to control the entire circuit, branch switch to control only this branch.
XIV, current 1, concept: 1 second through the conductor cross-section of the amount of charge called current, expressed in the symbol I. 2, unit: the international unit of current. 2, the unit: the international unit of current is amperage, referred to as ampere, with the symbol A.
3, the expression: I = Q / t = library / second = ampere, that is, a second through the conductor cross-section of the charge is 1 library, the current in the conductor is 1 ampere. 4, other common units: milliampere (mA), microampere (μA).
5, the conversion relationship: 1A = 103mA, 1mA = 103μA, 1A = 106μA 6, the size of the current macro-performance: on the same bulb: the greater the brightness, the higher the temperature, that is, the greater the effect of the current, the greater the current through the bulb. 7, measuring current size of the instrument, the dial is marked with an identification symbol: A ammeter. Fifteen, ammeter 1, how to correctly read the current representation: confirm that you use the range of the ammeter, according to the range to confirm the value of the current expressed in each large and each small grid, reading into the line of sight to the vertical surface.
2, the rules for the correct use of ammeters: (1) the ammeter must be connected in series in the circuit under test; (2) the current must be made from the ammeter's "+" terminal into the "-" terminal flow.