Output Devices in A-Level Physics | CIE A-Level 物理输出设备

📚 Output Devices in A-Level Physics | CIE A-Level 物理输出设备

In CIE A-Level Physics, electronics questions often ask you to describe how a sensing circuit produces a useful output, or to calculate the series resistor needed for an LED. An output device is the final transducer in a system: it changes an electrical signal into light, sound, movement or another physical quantity. This article examines the main output devices in the syllabus, their working principles, key equations and common exam traps.

在 CIE A-Level 物理中，电子学题目常要求你描述传感电路如何产生有用输出，或计算 LED 所需的串联电阻。输出设备是系统中的最终换能器：它将电信号转换为光、声、运动或其他物理量。本文梳理大纲中的主要输出设备、工作原理、关键公式与常见考试陷阱。

1. What is an Output Device? | 什么是输出设备？

An output device is any component that receives an electrical signal and converts it into a non-electrical form of energy. Typical output forms are light, sound, mechanical movement, and heat. In a sensing circuit, the sequence is usually input transducer → processor → output device. For example, a thermistor senses temperature, an op-amp or transistor switches current, and an LED or buzzer gives the visible or audible warning.

输出设备是接收电信号并将其转换为非电能形式的元件。常见的输出形式有光、声、机械运动和热。在传感电路中，顺序通常为输入换能器 → 处理器 → 输出设备。例如，热敏电阻感测温度，运算放大器或晶体管切换电流，LED 或蜂鸣器给出可见或可听的警报。

You should be able to distinguish an input transducer from an output transducer. An LDR or thermistor is an input device because it changes light or heat into a change in resistance, whereas an LED or loudspeaker is an output device because it produces light or sound from an electrical signal.

你应能区分输入换能器与输出换能器。光敏电阻或热敏电阻是输入设备，因为它们将光或热转换为电阻变化；而 LED 或扬声器是输出设备，因为它们从电信号产生光或声音。

2. Energy Conversion in Output Devices | 输出设备中的能量转换

All output devices obey conservation of energy. The electrical energy delivered to the device is partly converted into the desired output form and partly wasted, usually as internal heat. Efficiency is defined as useful output energy divided by total input energy, and can be expressed as a percentage.

所有输出设备都遵守能量守恒。输送给设备的电能部分转化为所需的输出形式，部分通常以内能形式浪费。效率定义为有用输出能量除以总输入能量，可用百分数表示。

Efficiency = ( useful output energy / total input energy ) ×