2020/9/18,通信与信息工程专业英语教程,1,Chapter 2 Circuit System and Design,Outline 2.1 Circuit and System 2.2 Analog and Digital Circuits Design 2.3 Radio Receiver Circuit,2020/9/18,通信与信息工程专业英语教程,2,2.1 Circuit and System,Outline Basic concepts Circuit and System,2020/9/18,通信与信息工程专业英语教程,3,Terminology,charge n.负荷, 电荷, 费用, 主管, 充电, 充气, 装料 conductivity n.传导性, 传导率 insulator n.绝缘体, 绝热器 gravitational adj.重力的 voltage n.电工电压, 伏特数 volts n.直流电压 ampere n.安培 ohm n.物欧姆 coulomb n.电库仑(电量单位) diameter n.直径 inductance n.感应系数, 自感应,2020/9/18,通信与信息工程专业英语教程,4,dielectric n.电介质, 绝缘体 adj.非传导性的 farad n.电法拉(电容单位) polarity n.极性 potential difference 电电位差，电势差 equivalent resistance 等效电阻 Superposition Theorem 叠加定理 Thevenins Theorem 戴维南定理 Norton s Theorem 诺顿定理,2020/9/18,通信与信息工程专业英语教程,5,In the Bohr theory of the atom (named after Niels Bohr, 18851962), electrons orbit a nucleus containing neutrons and protons. Electric charge is measured in coulombs. This relative mobility of electrons within a material is known as electric conductivity. Conductivity is determined by the types of atoms in a material (the number of protons in each atoms nucleus, determining its chemical identity) and how the atoms are linked together with one another.,Introduction,Text tour,Basic concepts Charge and conductivity,2020/9/18,通信与信息工程专业英语教程,6,It should also be understood that some materials experience changes in their electrical properties under different conditions. While the normal motion of free electrons in a conductor is random, with no particular direction or speed, electrons can be influenced to move in a coordinated fashion through a conductive material. This uniform motion of electrons is what we call electricity, or electric current. There can be electric current only where there exists a continuous path of conductive material providing a conduit for electrons to travel through. If the path is blocked, the flow will not occur.,2020/9/18,通信与信息工程专业英语教程,7,Electric circuits, voltage and current,An electric circuit is formed when a conductive path is created to allow free electrons to continuously move. This continuous movement of free electrons through the conductors of a circuit is called a current, and it is often referred to in terms of flow, just like the flow of a liquid through a hollow pipe. The force motivating electrons to flow in a circuit is called voltage, which technically is a measure of potential energy per unit charge of electrons. The more mass something has and the higher we lift it, the more potential energy it has.,2020/9/18,通信与信息工程专业英语教程,8,One volt is defined as that magnitude of electromotive force required cause a current of one ampere to pass through a conductor having a resistance of one ohm. Current flow is represented by the letter symbol I. The basic unit in which current is measured is the ampere (amp). One ampere of current is defined as the movement of one coulomb past any point of a conductor during one second of time.,2020/9/18,通信与信息工程专业英语教程,9,Free electrons tend to move through conductors with some degree of friction, or opposition to motion. This opposition to motion is more properly called resistance. The resistance of a material that follows Ohms law is constant, or independent of voltage or current, and the relationship between current and voltage is linear. Whenever an electric voltage exists between two separated conductors, an electric field is present within the space between those conductors. Electrical energy can be stored in an electric field. The device to be capable of doing this is called a capacitor or a condenser.,Resistance, capacitance and inductance,2020/9/18,通信与信息工程专业英语教程,10,If a condenser is connected to a battery, the electrons will flow out of the negative terminal of the battery and accumulate on the condenser plate connected to that side. Thus the condenser is said to be charged. The capacitance is directly proportional to the dielectric constant of the material and to the area of the plates and inversely to the distance of the plates. The larger the plate area, the smaller the space between them, the greater the capacitance. Whenever electrons flow through a conductor, a magnetic field will develop around that conductor. This effect is called electromagnetism. Magnetic energy can be stored in a magnetic field. The device to be capable of doing this is called an inductor.,2020/9/18,通信与信息工程专业英语教程,11,To store more energy in an inductor, the current through it must be increased. This means that its magnetic field must increase in strength, and that change in field strength produces the corresponding voltage according to the principle of electromagnetic self-induction. When the current through an inductor is increased, it drops a voltage opposing the direction of electron flow, acting as a power load. In this condition the inductor is said to be charging, because there is an increasing amount of energy being stored in its magnetic field. Note the polarity of the voltage with regard t