初三复习材料docWord格式文档下载.docx

1、 the number of times the object vibrates in a second, the unit of frequency is Hertz, the symbol Hz. The higher the frequency, the higher the pitch, the lower the frequency, the lower the pitch（2） loudness: the strength of the sound, the strength of the sound in dB. Amplitude: the amplitude of the v

2、ibration of an object, the larger the amplitude, the greater the sound, the smaller the amplitude, the smaller the sound The sound is also related to the distanee, the sound from the same source, the farther away from the source, the weaker the sound. （3） timbre: characteristics of sound The factors

3、 that determine the sound color: the material, structure, etc Distinguish sounds by distinguishing sound from sound 5, man，s hearing frequency for 20 hz - 20000 hz （1） time: less than 20 hz frequency sound, features: long transmission distance, pervasive, and so on, mainly in major natural disasters

4、: earthquakes, tsunamis, volcanic eruptions, typhoons, explosion, etc，（2） ultrasound: the sound of the frequency above 20000 hz, features: directional good, strong penetrating power, easy to get a sound energy from a relatively concentrated, can be used in the distance, speed, cleaning, welding, gra

5、vel etc. 6, the meaning of: （1） noise sound body do random vibration sound （physical perspective）（2） the sound that interferes with normal rest, learning and work, and the sound of interference in the sound of people listening（environmental protection） 7 noise levels and hazards: greater than 50dB,

6、which affects rest and sleep. Greater than 70dB affects learning and work; Greater than 90dB will damage your hearing Control noise: reduce noise in the source, reduce noise in the transmission process, and reduce noise in the ear The use of sound: （1） the use of sound to convey informat io n. When

7、sound encountered obstacles in the process of transmission, voice echoes will be reflected form, according to the time the voice returned, can determine the location of the obstacles The /zsonarz，device, which is now used to detect the ocean floor, is used by medical b-super to make use of the echo

8、principle （2） using sound waves to transmit energy. Such as sound waves can be used to clean clocks and other precision machinery; Surgeons can use ultrasonic vibrations to remove stones from the body. The second chapter, the phenomenon of light, the light straight line dissemination 1. the characte

9、ristics of the light source Light source refers to the object giving out light itself cdn, the light of the sun, glowing, lit candles are light, some object itself does not shine, but because they can reflect sunlight or other sources of light, as if they are shining, don，t be mistaken for a light s

10、ource, such as the moon and all the planets, they are not referred to in physics of the light sourceIn the course of friction, the rubber bar, which is bound by the nucleus of the nucleus, has attracted the past, so the rubber stick has an equal amount of negative charge because of excess electrons

11、When the solid matter is charged with friction, the charge that happens to move is negative charge, which is the free electron, the positive charge does not move the target of the 9 charge to form the current,The positive charge move in the direction of the rules for the direction of current, metal

12、conductive move when the charge is free electrons, which move in opposite direction with the direction of current, conductor conductive by free charge, acid, alkali, salt aqueous solution conductive by positive and negative ions 10, easily conductive object is called a conductor, common conductors a

13、re metals, graphite, the earth, the human body, as well as acid, alkali, salt solution, conductor easily conductive because there is a lot of free moving charges from a conductor. 11, it is not easy to conductive objects called insulators, common insulators are ceramics, rubber, glass, plastic, oil,

14、 etc，an insulator is not easy to conductive because insulators in almost no charge can be free to move Chapter 4 circuit cur re nt voltage 1. Power supply: device that provides continuous current （or voltage） Power is the conversion of other forms of energy intoelectricity. For example, dry cells co

15、nvert chemical energy into electricity A generator is converted by mechanical energy into electricity. The condition of continuous current: must have power supply and circuit closing The circuit consists of electrical power, wire, switch and electrical appliances The circuit has three states: （1） ac

16、cess: the circuit that is connected is called the path; （2） the broken circuit: the broken circuit is called open road: （3） short circuit: the circuit directly connected to the source of the power source is called a short circuit Circuit diagram: a diagram of a circuit connected by a symbol is calle

17、d a circuit diagram Series: the circuit that connects the circuit elements in successive connections The circuit in which the circuit component is connected together is called paralle 1. The size of the current is indicated by the current strength （short for current） The unit of current I is: the in

18、ternational unit is: ampere （A）: Common units are: mi Ilian （mA）, microan （A）. 1 ampere 二 103 mi Ilian 二 106 microampere The meter of the measuring current is: the ammeter, which is used in the following rules: the meter is in series in the circuit; The connection of the terminal post is correct, an

19、d the current is entered from the + terminal, from the termina 1. The measuring current shall not exceedthe range of the current meter; It is absolutely not allowed to connect the current meter to the poles of the power supply without using the appliance There are two ranges commonly used in the lab

20、oratory: 0 0.6, and the current value of each small lattice is 0. 02. From 0 to 3, the current value of each small lattice is 0. 1 Ann. Voltage （U） : voltage is the cause of electric current in the circuit The power supply is the device that provides voltage The unit of voltage U is: volt （V）: KV, m

21、illivolt （mV）, and microvolt （V）. One kilovolt 二 103 volts 二 106 millivolts 二 109 microvolts The instrument of measuring voltage is: the voltmeter, which USES the rule: the voltmeter should be in parallel in the circuit The connection of the terminal post is correct, and the current is entered from

22、the + terminal, from the - termina 1. The measured voltage shall not exceed the range of the voltmeter; The voltmeter commonly used in the laboratory has two ranges: 1, 0、3 v, and each small lattice has a voltage value of 0. 1 volts 0 to 15 volts, each small lattice has a voltage of 0. 5 volts The v

23、oltage value of memorized: 1, 1 dry battery voltage 1.5 volts; 1 lead battery voltage is 2 volts; The family lighting voltage is 220 volts; The voltage to safety is no higher than 36 volts The industrial voltage is 380 volts Resistance （R） : the obstruction of the conductor to the current（a conducto

24、rs resistance to the current is greaterThe larger the number, the smaller the current of the conductor Resistance （R） 19 units: international units: ohm （Q）;Customary units are: megohm Q （M）, qian Q （K）. 1 trillion euros 二 103 Euro 1000 二 103 euro. 20 factors determining the size of resistance: the

25、resistance of the conductor is the nature of a conductor, it depends on the size of the conductor material, length, cross-sectional area, and the temperature（resistance and add in the conductor on both ends of the voltage and current through） 21 rheostat （slide rheostat and resistance box） : （1） sli

26、de rheostat principle: （1） change the resistance wire length to change resistance in the circuit Effect: changes the current and voltage in the circuit by changing the resistance in the circuit（3） nameplate, such as a slide rheostat marked 50 Q 2 a said: is the significance of maximum value is 50 Q,

27、 allows the maximum current is 2 a. Proper use: a. should be in series in circuit. B. The connection should be one go，z; C. you should adjust the resistors to the largest place before you get the electricity（2） resistance box: a rheostat that can represent a resistor Ohms law: the electric current i

28、n a conductor is proportional to the voltage in the conductors end, and inversely proportional to the resistance of the con ductor The formula: （） the unit: I, （A） ; U and V （V）; R - European （Q） 1 Ann 二 1 volt/o. The I, U and R in the formula must be in the same circuit; I have two quantities in I,

29、 U, and R, and I can take another quantity. The unit should be unified when calculating 4. The application of ohm，s law: （1） the same resistance, resistance is constant and has nothing to do with current and voltage, but add on both ends of the resistor voltage increases, the through current is increased（R 二 U/I） when the voltage is constant, the greater the resistance, the less the curr