1、Unit Basic Knowledge of ElectronicsLesson 3 AC, DC and Electrical Signals New Words positive pztiv a. 正的 frequency frikwnsi n. 频率 measure me v.n 测量 device divais n. 装置，设备 label leibl n. 标签 v. 贴标签于； amplitude mplitju:d n. 振幅 period prd n. 时期，周期 oscilloscope siluskup n. 示波器 millisecond mili,seknd n. 毫
2、秒 microsecond mili,seknd n. 微秒Phrases and Expressions Alternating Current 交流电 Direct Current 直流电 power supply 电源 electronic circuit 电子电路 electrical signal 电信号 peak voltage 峰值电压 peak-peak voltage 峰-峰值电压 effective value 有效值Notes1.The rate of changing direction is called the frequency of the AC and it
3、is measured in hertz (Hz) which is the number of forwards-backwards cycles per second. hertz (Hz) ：n.赫兹(电学频率单位)；赫(兹), 每秒周数频率单位 【大写】赫兹(德国物理学家) n.赫兹(电学频率单位)；【大写】赫兹(德国物理学家) cycles per second：每秒循环数 这种方向变化的速率称为交流信号的频率，单位是赫兹，它表示一秒内周期性变化的次数。2.The voltage-time graph on the fig.3-4 shows various properties o
4、f an electrical signal. voltage-time graph：电压时间曲线 图34的电压时间图显示了一个电信号的各种特性。3.The diagram shows a sine wave but these properties apply to any signal with a constant shape. sine wave： n.正弦波 cosine wave： n.余弦波 该图显示了一个正弦波，但这些特性适用于具有恒定形状的任何信号。4. Time period is the time taken for the signal to complete one
5、cycle. It is measured in seconds (s), but time periods tend to be short so milliseconds (ms) and microseconds (s) are often used. 1ms = 0.001s and 1s = 0.000001s. milliseconds (ms)：n.毫秒；微秒 microseconds (s)：micro-second n：微秒 周期是完成一个周期的信号所需要的时间。单位是秒，但是周期往往非常短，所以常用毫秒（ms）和微秒(s)。1ms =0.001s，1s=0.000001s。
6、5. 1kHz = 1000Hz and 1MHz = 1000000Hz. 千赫（kHz）和兆赫（MHz）。6. Frequency1/ time period and time period=1/ frequency. time period：周期 频率1/周期，周期1/频率Translation of TextsLesson 3 AC, DC and Electrical Signals Alternating Current (AC) Alternating Current (AC) flows one way, then the other way, continually reve
7、rsing direction. An AC voltage is continually changing between positive (+) and negative (-). The rate of changing direction is called the frequency of the AC and it is measured in hertz (Hz) which is the number of forwards-backwards cycles per second. 第第3课课 交流电，直流电以及电信号交流电，直流电以及电信号 交流电交流电 交流电流的方向从一
8、个方向转换成另一个方向，持续不断的转换（如图31和图32所示）。交流电压会持续不断的在正负两个极性之间交替变化。这种方向变化的速率称为交流信号的频率，单位是赫兹，它表示一秒内周期性变化的次数。 An AC supply is suitable for powering some devices such as lamps and heaters but almost all electronic circuits require a steady DC supply. 交流电源适用于给一些设备供电，如灯和加热器，但几乎所有的电子电路都需要一个稳定的直流电。 Direct Current (DC
9、) Direct Current (DC) always flows in the same direction, but it may increase and decrease. A DC voltage is always positive (or always negative), but it may increase and decrease. Electronic circuits normally require a steady DC supply which is constant at one value. Cells, batteries and regulated p
10、ower supplies provide steady DC which is ideal for electronic circuits. Lamps, heaters and motors will work with any DC supply. 直流电直流电 直流电流总是向同一个方向流动，但它可能增大或者减小。直流电的方向总是正的（或者总是负的），但它也可能增大或者减小（如图33所示）。电子电路通常需要一个具有定值的稳定的直流电源。干电池、蓄电池（组）和稳压电源能提供对于电子电路来说理想的、稳定的直流电。在直流电源作用下， 电灯，加热器和发动机将可以正常工作。 Properties
11、of electrical signals An electrical signal is a voltage or current which conveys information, usually it means a voltage. The term can be used for any voltage or current in a circuit. 电信号的特性电信号的特性 电信号是传送信息的电压或者电流，通常是指电压。这个术语可以被用于电路里任何一个电压或者电流。 The voltage-time graph on the fig.3-4 shows various prop
12、erties of an electrical signal. In addition to the properties labeled on the graph, there is frequency which is the number of cycles per second. The diagram shows a sine wave but these properties apply to any signal with a constant shape. 图34的电压时间图显示了一个电信号的各种特性。除了图上标明的那些特性以外还有频率，它表示每秒钟的周期数。该图显示了一个正弦
13、波，但这些特性适用于具有恒定形状的任何信号。 Amplitude is the maximum voltage reached by the signal. It is measured in volts, V. 振幅是信号所达到的最大电压。单位是伏特，V。 Peak voltage is another name for amplitude. 峰值电压是振幅的另一个名称。 Peak-peak voltage is twice the peak voltage (amplitude). When reading an oscilloscope trace it is usual to meas
14、ure peak-peak voltage. 峰峰值电压是峰值电压（振幅）的两倍。当对示波器上的轨迹进行读数的时候，我们通常测量峰峰值电压。 Time period is the time taken for the signal to complete one cycle. It is measured in seconds (s), but time periods tend to be short so milliseconds (ms) and microseconds (s) are often used. 1ms = 0.001s and 1s = 0.000001s. 周期是完成
15、一个周期的信号所需要的时间，单位是秒。但是周期往往非常短，所以常用毫秒（ms）和微秒(s)。1ms =0.001s，1s=0.000001s。 Frequency is the number of cycles per second. It is measured in hertz (Hz), but frequencies tend to be high so kilohertz (kHz) and megahertz (MHz) are often used. 1kHz = 1000Hz and 1MHz = 1000000Hz. 1kHz=1000Hz and 1MHz=1000000H
16、z。Frequency1/ time period and time period=1/ frequency. 频率是每秒的周期数。单位是赫兹（Hz），但频率往往比较高，所以常用千赫（kHz）和兆赫（MHz）。频率1/周期，周期1/频率。 Another value used is the effective value of AC. This is the value of alternating voltage or current that will have the same effect on a resistance as a comparable value of direct
17、voltage or current will have on the same resistance. 另一个常用的值是有效值，电压或电流有效值作用于电阻，与相同大小的直流电压或电流作用于相同大小的电阻等效。Exercises.Write T (True) or F (false) beside the following statements about the text.1.Direct Current (DC) flows one way, then the other way, continually reversing direction.2.Alternating Current
18、 (AC) always flows in the same direction. 3.Amplitude is the minimum voltage reached by the signal.4.Peak-peak voltage is twice the peak voltage (amplitude).5.The effective value of AC is the value of alternating voltage or current that will have the same effect on a resistance as a comparable value
19、 of direct voltage or current will have on the same resistance. Fill in the missing words according to the text.1.An AC voltage is continually changing between and . 2.Electronic circuits normally require a steady DC supply which is one value. 3.Cells, batteries and regulated power supplies provide
20、which is ideal for electronic circuits.4.In addition to the properties labeled on the graph, there is frequency which is the number of per second. 5.When reading an oscilloscope trace it is usual to measure voltage. . Match the following terms to appropriate definition or expression.1.An electrical signal 1/ time period 2.Peak voltage the maximum voltage reached by the signal3.Peak-peak voltage twice the peak voltage (amplitude)4.Frequency a voltage or current which conveys informationEnd
