Which of the following is commonly used as a visual indicator?
The correct answer is LED (Light Emitting Diode). An LED is commonly used as a visual indicator because it emits light when forward current flows through it. LEDs are ideal indicators because they're small, efficient, long-lasting, fast-responding, and available in various colors. For amateur radio operators, LEDs are found throughout equipment as power indicators, transmit indicators, signal strength displays, status lights, and warning indicators. They provide clear visual feedback about equipment status without consuming much power. Understanding LEDs helps when troubleshooting non-functioning indicators and when adding status lights to projects.
Exam Tip
LED = visual indicator. Think 'L'ED = 'L'ight 'E'mitting 'D'iode = visual indicator. FETs, Zener diodes, and transistors are signal-processing components, not light emitters.
Memory Aid
"LED = Light Emitting Diode = visual indicator. Think 'L'ED = 'L'ight 'E'mitting = 'L'ooks 'E'asy to see. Emits light for visual indication."
Real-World Application
Your transceiver has an LED that lights up green when power is on, and turns red when transmitting. This provides instant visual feedback about the radio's status. The LED consumes very little power (typically 10-20mA) but gives you clear information. Without the LED, you'd have no visual indication of the radio's state.
Key Concepts
Why Other Options Are Wrong
Option B (FET): Incorrect. A FET (Field-Effect Transistor) is a semiconductor device used for amplification or switching. It doesn't emit light - it processes electrical signals. FETs aren't visual indicators.
Option C (Zener diode): Incorrect. A Zener diode is used for voltage regulation or reference. It doesn't emit light - it maintains a constant voltage. Zener diodes aren't visual indicators.
Option D (Bipolar transistor): Incorrect. A bipolar transistor amplifies signals or switches circuits. It doesn't emit light - it processes electrical signals. Transistors aren't visual indicators.
题目解析
The correct answer is LED (Light Emitting Diode). An LED is commonly used as a visual indicator because it emits light when forward current flows through it. LEDs are ideal indicators because they're small, efficient, long-lasting, fast-responding, and available in various colors. For amateur radio operators, LEDs are found throughout equipment as power indicators, transmit indicators, signal strength displays, status lights, and warning indicators. They provide clear visual feedback about equipment status without consuming much power. Understanding LEDs helps when troubleshooting non-functioning indicators and when adding status lights to projects.
考试技巧
LED = visual indicator. Think 'L'ED = 'L'ight 'E'mitting 'D'iode = visual indicator. FETs, Zener diodes, and transistors are signal-processing components, not light emitters.
记忆口诀
LED = Light Emitting Diode = visual indicator. Think 'L'ED = 'L'ight 'E'mitting = 'L'ooks 'E'asy to see. Emits light for visual indication.
实际应用示例
Your transceiver has an LED that lights up green when power is on, and turns red when transmitting. This provides instant visual feedback about the radio's status. The LED consumes very little power (typically 10-20mA) but gives you clear information. Without the LED, you'd have no visual indication of the radio's state.
错误选项分析
Option B (FET): Incorrect. A FET (Field-Effect Transistor) is a semiconductor device used for amplification or switching. It doesn't emit light - it processes electrical signals. FETs aren't visual indicators. Option C (Zener diode): Incorrect. A Zener diode is used for voltage regulation or reference. It doesn't emit light - it maintains a constant voltage. Zener diodes aren't visual indicators. Option D (Bipolar transistor): Incorrect. A bipolar transistor amplifies signals or switches circuits. It doesn't emit light - it processes electrical signals. Transistors aren't visual indicators.
知识点
LEDs, Visual indicators, Status lights, Light emitting diodes
Verified Content
Question from official FCC Technician Class question pool. Explanation reviewed by licensed amateur radio operators.