📚 Systematic Error in A-Level Physics | 系统误差
In A-level Physics, a systematic error is a constant bias that shifts every measurement away from the true value in the same direction. It affects the accuracy of an experiment, not its precision. AQA practical exam questions often ask you to identify systematic errors and suggest how to reduce them.
在 A-level 物理中，系统误差是一种恒定偏差，使每次测量都朝同一方向偏离真值。它影响实验的准确度，而非精密度。AQA 实验考试题常要求你识别系统误差并提出减少方法。
1. What Is a Systematic Error? | 什么是系统误差？
A systematic error is a reproducible inaccuracy caused by a fault in the measuring system, the method or the model. Since the error pushes every reading the same way, repeating the experiment does not average it away. The error between a measured value and the true value can be written as:
系统误差是由测量系统、方法或模型缺陷导致的可重复偏差。由于误差以相同方式影响每一次读数，重复实验无法将其平均掉。测量值与真值之间的误差可写为：
error = measured value − true value
For a systematic error, the average measured value is consistently above or below the true value. The sign and size of the offset stay roughly constant when the same instrument and method are used.
对于系统误差，平均测量值始终高于或低于真值。当使用相同仪器和方法时，偏移的符号和大小大致保持不变。
2. Systematic vs Random Errors | 系统误差与随机误差
Random errors cause readings to be scattered symmetrically about the mean. They can be reduced by taking repeats and calculating a mean. Systematic errors shift the mean itself, so averaging cannot reveal or remove them.
随机误差使读数围绕平均值对称分布，可以通过重复测量并取平均来减小。系统误差使平均值本身偏移，因此取平均无法揭示或消除它。
| Feature | Systematic error | Random error |
| Direction | Same every time | Varies around the mean |
| Effect on mean | Shifts mean away from true value | Mean approaches true value with repeats |
| Effect of repeats | Does not reduce error | Reduces error |
| Affects | Accuracy | Precision |
| Examples | Zero error, calibration drift | Reaction time, electrical noise |
3. Accuracy, Precision and Validity | 准确度、精密度与有效性
Accuracy means closeness to the true value. A small systematic error means high accuracy. Precision means the closeness of repeated readings to each other. An experiment can be very precise but inaccurate if the instrument has a zero error.
准确度意为与真值的接近程度。系统误差小意味着准确度高。精密度意为重复读数彼此之间的接近程度。如果仪器存在零误差，实验可以非常精密但不准确。
Validity asks whether the method actually measures what it is intended to measure. A large systematic error can make a conclusion invalid because the recorded values do not represent the true physical quantity.
有效性考察方法是否真正测量了目标物理量。大的系统误差可能使结论无效，因为记录值不代表真实物理量。
4. Common Sources of Systematic Error | 系统误差的常见来源
Systematic errors often come from the apparatus itself, the environment or the procedure. The most common sources in school and A-level practical work are listed below.
系统误差通常来自仪器本身、环境或操作步骤。以下是中学和 A-level
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