📚 AS Physics PH01 Unit 1: Experimental Analysis and Evaluation | AS物理PH01单元1：实验分析与评估
Experimental investigations form the core of the AS Physics Unit 1 (PH01) assessment. The example responses provided by the exam board highlight how students should plan, carry out, and critically evaluate an experiment. This article breaks down the essential skills required – from identifying variables and handling uncertainties to plotting graphs and assessing sources of error – so you can understand exactly what examiners look for in a top‑band answer.
实验探究是AS物理单元1（PH01）考核的核心。考试局提供的示例答案揭示了学生应该如何规划、实施并批判性地评估一个实验。本文详细解析了所需的各项基本技能——从识别变量、处理不确定性，到绘制图表和评估误差来源——帮助你准确理解阅卷人在高分答案中寻找的要点。
1. Understanding the Mark Scheme | 理解评分标准
Before writing any practical answer, familiarise yourself with the assessment objectives. In PH01, marks are awarded for clear planning, safe and effective procedure, accurate recording of data, correct uncertainty calculations, appropriate graphical analysis, and a thorough evaluation.
在动笔撰写任何实验答案之前，请先熟悉评分目标。在PH01中，分数分布在清晰的计划、安全有效的步骤、准确的数据记录、正确的不确定性计算、合适的图像分析以及全面的评估上。
Example responses often show that candidates fail to link their conclusions back to the raw data. The mark scheme rewards references to specific numerical comparisons, such as ‘the two values of g differ by less than 5%, so the experiment supports the relationship within experimental uncertainty’.
示例答案通常暴露出考生未能将结论与原始数据联系起来。评分标准会奖励那些引用具体数值比较的回答，例如“两个g值相差不到5%，因此该实验在实验不确定度范围内支持该关系”。
Always check whether you need to calculate a percentage difference, compare measurements, or discuss the validity of a hypothesis using your results.
务必核查是否需要计算百分比差异、比较测量值，或利用你的结果讨论假设的有效性。
2. Identifying Variables and Control | 变量识别与控制
Every experiment begins with a clear statement of the independent, dependent, and control variables. For instance, when investigating the resistivity of a wire, the independent variable might be the length of the wire, the dependent variable the resistance, while temperature and material become key control variables.
每个实验都始于清晰地陈述自变量、因变量和控制变量。例如，在探究导线电阻率时，自变量可能是导线的长度，因变量为电阻，而温度和材料则成为关键的控制变量。
In the example responses, candidates who explicitly explain how they controlled confounding factors – such as using a constant‑temperature bath or waiting for readings to stabilise – score more highly than those who simply list variables.
在示例答案中，那些明确说明如何控制干扰因素的考生——比如使用恒温水浴或等待读数稳定——会比仅仅罗列变量的考生得分更高。
Control variables must be kept constant to ensure that any change in the dependent variable is solely due to the independent variable. This is a fundamental concept tested in PH01.
控制变量必须保持恒定，以确保因变量的任何变化完全源于自变量。这是PH01中考查的一个基本概念。
3. Planning an Experiment | 实验设计
A good experimental plan includes a labelled diagram of the apparatus, a step‑by‑step procedure, and a clear indication of the range and intervals for data collection. Examiners want to see that you have considered how to obtain reliable data, not just a sketch.
一个好的实验计划应包括标有注释的仪器示意图、逐步操作步骤，以及数据采集的范围和间隔的明确说明。阅卷人希望看到你考虑了如何获得可靠数据，而不仅仅是一幅草图。
For example, when measuring the acceleration of free fall using a light gate, you should specify the height range (e.g. 0.200 m to 1.000 m in 0.100 m steps) and justify why you chose at least six different heights to minimise random error in the gradient.
例如，当使用光电门测量自由落体加速度时，你应当指定高度范围（如0.200 m到1.000 m，步长0.100 m），并说明为何至少选取六个不同高度以最小化梯度中的随机误差。
The plan must also mention how to ensure safety: low voltage supplies, careful handling of masses, or fastening stands securely. This is often overlooked in weaker responses.
实验计划还必须提及如何确保安全：低压电源、小心处理砝码，或牢固固定支架。这一点在较薄弱的回答中常被忽略。
4. Measurement Techniques and Instruments | 测量技术与仪器
Selecting the appropriate measuring instrument is critical. In PH01 example responses, candidates who choose a micrometer screw gauge (precision ±0.01 mm) to measure the diameter of a thin wire instead of a ruler (precision ±1 mm) demonstrate awareness of precision and its impact on overall uncertainty.
选择合适的测量仪器至关重要。在PH01示例答案中，考生选用千分尺（精度±0.01 mm）而不是直尺（精度±1 mm）来测量细导线的直径，体现了对精度及其对总不确定度影响的认识。
Always state the resolution of each instrument and use it to estimate the absolute uncertainty in a single reading. For a digital meter, the uncertainty is usually the smallest readable digit; for an analogue scale, it is often half the smallest division.
始终说明每台仪器的分辨率，并用它来估算单次读数的绝对不确定度。对于数字仪表，不确定度通常是最小可读位；对于模拟刻度，通常是其最小分度值的一半。
Repeated measurements reduce random error. You should take at least three readings and calculate a mean, quoting the range or the half‑range as a measure of uncertainty if no other estimate is available.
重复测量能减小随机误差。你应当至少读取三个读数并计算平均值，在没有其他估计方法时，以极差或半极差作为不确定度的度量。
5. Recording and Tabulating Data | 记录与表格数据
Data tables must have clear headings with units and the uncertainty in each column. A common mistake seen in example responses is omitting units from column headers – marks are deducted because the table is incomplete.
数据表必须有清晰的表头，包含单位和每列的不确定度。示例答案中常见的错误是表头缺失单位——表格不完整会被扣分。
Record raw data to the precision of the instrument. If you measure a length as 25.0 cm on a ruler with 1 mm marks, write ‘25.0’ not ’25’. Consistent significant figures convey a correct appreciation of precision.
按照仪器的精度记录原始数据。如果用毫米刻度的直尺测出一个长度为25.0 cm，就应写成“25.0”而不是“25”。小数点后一致的数字反映了对精度的正确理解。
Include a calculated mean and the percentage uncertainty for any derived quantity. For instance, if the diameter d = 0.46 ± 0.01 mm, the percentage uncertainty is (0.01/0.46)×100% ≈ 2.2%, which propagates through equations.
应包含计算出的平均值和任何导出量的百分比不确定度。例如，如果直径 d = 0.46 ± 0.01 mm，那么百分比不确定度为 (0.01/0.46)×100% ≈ 2.2%，这种不确定度会通过公式传递。
6. Calculating Uncertainties | 不确定性计算
Understanding uncertainty propagation is essential for PH01. When adding or subtracting quantities, absolute uncertainties add. When multiplying or dividing, percentage uncertainties add.
理解不确定度的传递对PH01至关重要。加、减运算时，绝对不确定度相加。乘、除运算时，百分比不确定度相加。
If a quantity is raised to a power, such as d², the percentage uncertainty is multiplied by that power. For example, the percentage uncertainty in cross‑sectional area A = π(d/2)² is twice the percentage uncertainty in the diameter.
若一个量被乘方，例如 d²，其百分比不确定度应乘以该方次。例如，横截面积 A = π(d/2)² 的百分比不确定度是直径百分比不确定度的两倍。
A useful summary table:
| Operation | Uncertainty Rule |
|---|---|
| Addition / Subtraction | Add absolute uncertainties ΔQ = ΔA + ΔB |
| Multiplication / Division | Add percentage uncertainties %Q = %A + %B |
| Power, e.g. Aⁿ | Multiply percentage uncertainty by n: %Q = n × %A |
一个实用的总结表：
| 运算 | 不确定度规则 |
|---|---|
| 加法 / 减法 | 绝对不确定度相加 ΔQ = ΔA + ΔB |
| 乘法 / 除法 | 百分比不确定度相加 %Q = %A + %B |
| 乘方，例如 Aⁿ | 百分比不确定度乘以 n：%Q = n × %A |
7. Plotting Graphs and Error Bars | 绘图与误差线
In AS Physics Unit 1, you are frequently asked to plot a straight‑line graph and use its gradient. Use a sharp pencil, label axes with quantity and unit (e.g. ‘T² / s²’), and choose scales that occupy at least half of the graph paper in both directions.
在AS物理单元1中，你经常需要绘制一条直线图并利用其斜率。请使用削尖的铅笔，用物理量和单位标记坐标轴（例如“T² / s²”），并选择能让数据点在两个方向上都至少占据一半图纸的标度。
Error bars represent the absolute uncertainty in each plotted value. If the uncertainty is too small to draw a clear bar, state this and note that they are not visible. Include both horizontal and vertical error bars when both variables have significant uncertainty.
误差线表示每个数据点的绝对不确定度。如果不确定度太小而无法画出清晰的误差线，请说明这一情况并指出它们不可见。当两个变量都有显著不确定度时，应同时绘制水平和垂直误差线。
In the example responses, candidates who plot accurate error bars and use them to discuss the scatter of points generally achieve higher marks for analysis.
在示例答案中，准确绘制误差线并利用它们讨论数据点离散程度的考生通常能在分析部分获得更高分数。
8. Drawing Lines of Best Fit and Worst Fit | 最佳拟合与最差拟合线
The line of best fit should pass through as many points as possible, balancing those above and below the line. Do not force it through the origin unless the theoretical relationship demands it and your data support that choice.
最佳拟合线应尽可能多地穿过数据点，并使线上、线下的点数大致平衡。不要强制通过原点，除非理论关系要求如此且你的数据也支持这一选择。
To estimate the uncertainty in the gradient, draw two additional lines: the steepest and shallowest reasonable straight lines that still pass through the error bars. These are often called the ‘worst fit’ lines. The uncertainty in gradient is:
Δm = (mₘₐₓ – mₘᵢₙ) / 2
要估算梯度的不确定度，可额外绘制两条线：穿过误差线的最陡和最浅的合理直线，它们常被称为“最差拟合”线。梯度的不确定度为：
Δm = (m_max – m_min) / 2
Examiners look for these lines drawn with a ruler and clearly labelled. The same method can be used to find the uncertainty in the y‑intercept.
阅卷人期望看到这些线用直尺绘制并清晰标记。相同的方法也可用于求得y轴截距的不确定度。
9. Determining Gradient and Intercept | 计算斜率与截距
Calculate the gradient using a large triangle, showing clearly the coordinates of the two points you used. State the formula:
m = (y₂ – y₁) / (x₂ – x₁)
用一个大三角形计算斜率，清楚标明所用两点的坐标。写出公式：
m = (y₂ – y₁) / (x₂ – x₁)
The y‑intercept c is read directly from the graph where the line crosses the y‑axis. Both gradient and intercept must be given with appropriate units and their absolute uncertainties, rounded to the same number of decimal places as the uncertainty.
y轴截距 c 直接从图中直线与y轴的交点读出。斜率和截距均需带有合适的单位及其绝对不确定度，并四舍五入到与不确定度相同的小数位数。
In PH01, typical relationships tested include V = IR, v² = u² + 2as, and T = 2π√(L/g). Relating the gradient to a physical constant (e.g. g = 4π²/m) and calculating its experimental value and percentage difference from the accepted value is a key skill.
在PH01中，考查的典型关系包括 V = IR、v² = u² + 2as 和 T = 2π√(L/g)。将斜率与物理常数关联（例如 g = 4π²/m），计算其实验值以及与公认值的百分比差异，是一项关键技能。
10. Evaluating Results and Sources of Error | 结果评估与误差来源
Evaluation requires you to identify the main sources of uncertainty or error and classify them as systematic or random. For example, a zero error on a voltmeter is a systematic error; reaction time in starting a stopwatch leads to random error.
评估部分要求你辨认主要的不确定度或误差来源，并将其归类为系统误差或随机误差。例如，电压表的零点误差是系统误差；启动秒表的反应时间则导致随机误差。
Refer back to your data: if the line of best fit does not pass through the origin despite a theoretical prediction, a systematic error may be present. Percentage differences between experimental and accepted values help quantify the credibility of your results.
回头分析你的数据：如果最佳拟合线没有如理论预测那样通过原点，则可能存在系统误差。实验值与公认值之间的百分比差异有助于量化结果的可信度。
In the example responses, effective candidates state which measurement contributed most to the overall uncertainty and explain why, often based on the percentage uncertainty of each variable.
在示例答案中，得高分的考生会指出哪个测量对总不确定度贡献最大，并解释原因，通常基于每个变量的百分比不确定度。
11. Suggesting Improvements | 改进建议
Proposed improvements must be specific and linked to the identified sources of error. Rather than a generic ‘use more accurate instruments’, you could say: ‘use a digital calliper instead of a ruler to reduce the percentage uncertainty in the measurement of the wire’s diameter from 5 % to 0.5 %’.
提出的改进措施必须具体，并与已识别的误差来源相关联。不要泛泛而谈“使用更精确的仪器”，你可以说：“使用数显卡尺代替直尺，将导线直径测量的百分比不确定度从5%降低到0.5%”。
Additional improvements might include increasing the number of data points, extending the range of measurements, controlling temperature more strictly, or using data‑logging equipment to reduce reaction‑time errors.
其他改进措施可能包括增加数据点数量、扩大测量范围、更严格地控制温度，或使用数据采集设备以减少反应时间误差。
Examiners also reward suggestions that are practical and cost‑effective within a typical school laboratory. Avoid suggesting equipment that would be unavailable or unfeasible.
阅卷人同样青睐那些在典型学校实验室中切实可行且成本合理的建议。避免建议无法获得或不可行的设备。
12. Common Mistakes in Practical Responses | 常见回答错误
The example responses for PH01 reveal several recurring mistakes: confusing precision with accuracy, failing to include units or uncertainties in tables, forcing the best‑fit line through the origin without justification, and drawing error bars that are too small to be visible yet not commenting on them.
PH01的示例答案揭示了几个反复出现的错误：混淆精度与准确度，表格中遗漏单位或不确定度，无理由地将最佳拟合线强制通过原点，以及绘制了过小、不可见的误差线却不加说明。
Another common error is treating all uncertainties as absolute when a percentage treatment is needed, or misidentifying a systematic error as random. Practice writing concise, quantitative evaluations that directly compare numbers.
另一个常见错误是把所有不确定度都当作绝对不确定度处理，而实际上需要百分比处理，或者将系统误差误判为随机误差。请练习撰写简明、量化的评估，直接进行数字比较。
Finally, always read the question carefully: some investigations require you to determine a constant, while others ask you to verify a relationship. Your analysis and conclusion must match the stated aim.
最后，务必仔细审题：有些探究要求你测定一个常数，而另一些则要求你验证一种关系。你的分析和结论必须与所陈述的目标相符。
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