CRAC Class C (2025) — Questions 1001–1010
U1086. Which of the following components allows current to flow in only one direction?
以下哪种元器件只允许单方向的电流流动？
Exam tips · 考试提示
A 二极管 (diode) conducts primarily in one direction (forward) and blocks the other (reverse). A battery, transformer, and relay do not inherently restrict current to one direction, so B/C/D are wrong.
U1087. What are the two electrodes of a diode called?
二极管的两个电极分别叫什么？
Exam tips · 考试提示
A diode's two terminals are the 正极/负极 (positive/negative), equivalently the 阳极/阴极 (anode/cathode). Source/drain (B) belong to FETs; cathode/plate (C) to vacuum tubes; gate/base (D) to thyristors/transistors.
U1088. How can you identify the cathode (negative terminal) of a semiconductor diode by its appearance?
如何根据外观识别半导体二极管的负极？
Exam tips · 考试提示
The standard visual cue for a diode's cathode is a band or ring printed near that end of the body (A). Diodes are not normally printed with the word "Cathode" (B), the leads are the same length (C), and D describes features of some vacuum tubes, not semiconductor diodes.
U1089. What device does the abbreviation LED stand for?
LED是哪种器件的缩写？
Exam tips · 考试提示
LED = 发光二极管 (light-emitting diode), a diode that emits light when forward-biased. LCD, CRT, and beam tetrode are unrelated devices.
U1090. Among the following devices, which can be used as an indicator lamp?
在下列器件中，能够用作指示灯的是：
Exam tips · 考试提示
An LED (发光二极管) emits visible light and is the standard indicator lamp. A BJT is an amplifier/switch, a TVS is a surge protector, and an SCR is a power-switching thyristor — none serves as a light indicator, so B/C/D are wrong.
U1091. What must be observed when connecting an LED to a DC supply?
将发光二极管接到直流电源上需要注意什么？
Exam tips · 考试提示
An LED must be forward-biased to light and must have a series current-limiting resistor to keep current within rating (A). Reverse connection won't light it (B); a parallel resistor won't limit current (C); direct connection (D) burns it out.
U1092. Which of the following components can convert alternating current into pulsating direct current?
下列哪种部件可以把交变电变成脉动直流电？
Exam tips · 考试提示
A 二极管整流器 (diode rectifier) passes only one polarity of AC, producing pulsating DC. A transformer changes voltage but not polarity, a comparator/amplifier conditions signals, and an emitter follower buffers — none rectifies, so B/C/D are wrong.
U1093. The forward conduction voltage drop of a silicon rectifier diode is approximately:
硅整流二极管的正向导通压降大约为：
Exam tips · 考试提示
A silicon rectifier diode has a forward drop of about 0.7 V (A). 0.3 V is typical of Schottky/germanium (B); tens of mV is far too low; 1000 V is a reverse breakdown rating, not a forward drop.
U1094. When reading a circuit diagram or running a circuit simulation, if you see the symbol "BJT", it denotes:
阅读电路图或运行计算机电路仿真时，如果看到符号"BJT"， 则为：
Exam tips · 考试提示
BJT = 双极型三极管 (bipolar junction transistor), a current- controlled three-terminal device. Dual-gate FET, JFET, and unijunction transistor are different devices, so B/C/D are wrong.
U1095. The three basic electrodes of a field-effect transistor are:
场效应晶体管的三个基本电极是：
Exam tips · 考试提示
A 场效应晶体管 (FET) has three terminals: 源极/栅极/漏极 (source/gate/drain). Cathode/grid/plate (B) are vacuum-tube terms; emitter/base/collector (C) are BJT; cathode/gate/anode (D) are thyristor/SCR terms.