📚 AQA AS Physics PH02: June 2022 Practical Investigation Exam Report | AQA AS物理PH02：2022年6月实验探究考试报告
The AQA AS Physics PH02 paper for the June 2022 series included a substantial practical investigation section designed to assess candidates’ experimental skills, data analysis, and evaluation abilities. This report summarises the key observations from the examiner’s feedback, highlighting common pitfalls and offering guidance to improve performance in similar tasks. The focus is on the free-fall experiment to determine g, but the underlying principles apply to all AS practical work.
AQA AS物理PH02试卷在2022年6月的考试中包含了一个重要的实验探究部分，旨在评估考生的实验技能、数据分析和评估能力。本报告总结了考官的反馈要点，突出常见错误，并为提高类似任务中的表现提供指导。虽然重点是测量重力加速度g的自由落体实验，但其基本原理适用于所有AS阶段的实验工作。
1. Overview of the PH02 Practical Component | PH02实验部分概述
The practical component in PH02 requires candidates to demonstrate a clear understanding of experimental design, accurate data collection, and thorough evaluation. In the June 2022 paper, the investigation centred on measuring the acceleration due to gravity, g, using a free-fall method. Candidates were expected to record repeat readings, calculate mean times, determine uncertainties, plot a suitable graph, and draw meaningful conclusions. The examiners noted that while many students followed the procedure correctly, a significant number lost marks due to poor data handling and superficial error analysis.
PH02中的实验部分要求考生展示对实验设计、准确数据收集和全面评估的清晰理解。在2022年6月的试卷中，探究主题是通过自由落体法测量重力加速度g。考生需要记录重复读数、计算平均时间、确定不确定度、绘制合适的图表并得出有意义的结论。考官指出，虽然许多学生正确地遵循了操作步骤，但相当一部分学生因数据处理不佳和误差分析流于表面而失分。
2. The Free-Fall Method for g | 测量g的自由落体法
The experiment involved dropping a steel ball from rest through a measured height s, and using light gates or a stopwatch to measure the time of fall t. The relationship s = ½gt² was then applied, rearranged to g = 2s / t². Candidates needed to recognise that plotting s against t² would yield a straight line with gradient ½g, thereby allowing g to be determined from the slope. This linearisation technique is fundamental in A-level physics and tests the ability to manipulate equations into a y = mx + c form.
该实验包括从静止释放一个钢球，让其下落已知高度s，并利用光门或秒表测量下落时间t。使用的方程为s = ½gt²，变形后得到g = 2s / t²。考生需要认识到，绘制s‑t²图会得到一条直线，其斜率为½g，从而可以通过斜率求出g。这种线性化方法是A‑level物理的基础，考查了将方程整理为y = mx + c形式的能力。
3. Common Errors in Distance Measurement | 距离测量中的常见错误
A frequent mistake was the inaccurate measurement of the drop height s. Many candidates measured from the bottom of the ball at release to the top of the landing pad, whereas the correct distance should be from the bottom of the ball to the landing surface when the timing stops – typically the same reference point. This could introduce a systematic error of several millimetres. Examiners emphasised using a metre ruler with a clear perpendicular line of sight and, if possible, a set square to align the ruler vertically.
一个常见的错误是下落高度s的测量不准确。许多考生测量的是释放时球底到落垫顶部的距离，而正确的距离应该是球底到计时停止时的落面——通常采用同一参考点。这可能会引入几毫米的系统误差。考官强调，应使用米尺并确保视线垂直，如果可能的话，使用三角板来确保尺子竖直对齐。
4. Timing Issues and Reaction Time Effects | 计时问题与反应时间影响
When using manual stopwatches, reaction time introduces random uncertainties. Candidates were expected to repeat each height measurement at least three times and calculate a mean time. However, many failed to recognise that a single anomalous result could skew the mean; the examiner report recommended identifying and discarding clear outliers. Furthermore, some students did not appreciate that a digital timer started and stopped by light gates eliminates reaction time entirely, which should be mentioned as an improvement in the evaluation section.
在使用手动秒表时，反应时间会引入随机不确定性。考生需要对每个高度至少重复测量三次，并计算平均时间。然而，许多人未能意识到，单个异常结果可能会扭曲平均值；考官报告建议识别并剔除明显的异常值。此外，一些学生没有认识到，由光门触发启动和停止的数字计时器能完全消除反应时间，这应在评估部分作为改进措施提及。
5. Data Recording and Significant Figures | 数据记录与有效数字
The raw data table presented by many candidates lacked consistency in significant figures. For instance, a time recorded as 0.54 s, 0.5 s, and 0.543 s for three trials indicated carelessness. All readings should be recorded to the same precision, typically to 0.01 s if the stopwatch reads to 10 ms, or to the resolution of the instrument. The mean should then be quoted to the same number of decimal places, not falsely increased precision. The examiners noted that the correct use of significant figures in the calculated value of g was also weak; many candidates gave g to 5 or 6 significant figures when the input data justified only 2 or 3.
许多考生提交的原始数据表在有效数字上缺乏一致性。例如，三次试验的时间记录为0.54 s、0.5 s和0.543 s，表明粗心大意。所有读数都应以相同的精度记录，如果秒表读数为10毫秒，则通常记录到0.01 s，或记录到仪器的分辨率。然后，平均值也应保留相同的小数位数，而不是虚假地提高精度。考官指出，g的计算值中有效数字的正确使用也很薄弱；许多考生给出的g有5或6位有效数字，而输入数据仅能支持2到3位。
6. Calculating Uncertainty in Time and Height | 时间与高度不确定度的计算
Uncertainty calculations were a major discriminator. For a single measurement of height using a metre ruler, the absolute uncertainty is typically ±1 mm or half the smallest division, but candidates often incorrectly used ±0.5 mm without justification. For time, when repeat readings were taken, the uncertainty could be estimated from the range (half the range) or the standard deviation, yet many simply quoted the instrument resolution (e.g., ±0.01 s) even though random scatter was larger. The examiners stressed the importance of using the larger of the instrument uncertainty and the spread of repeat readings as the absolute uncertainty.
不确定度的计算是一个主要的分水岭。对于使用米尺的单次高度测量，绝对不确定度通常为±1 mm或最小刻度的一半，但考生常无理由地使用±0.5 mm。对于时间，当进行了重复读数时，不确定度可以通过极差（极差的一半）或标准差来估算，然而许多人仅仅引用了仪器分辨率（例如±0.01 s），尽管随机散布更大。考官强调，应将仪器不确定度和重复读数的散布中的较大者作为绝对不确定度。
7. Graph Plotting and Line of Best Fit | 图形绘制与最佳拟合线
The examiner report highlighted poor graph skills. Many candidates plotted s against t instead of t², resulting in a curve that made gradient analysis impossible. Even when the correct axes were chosen, scales were often inappropriate – for instance, using 1 cm = 0.01 s² on the horizontal axis, which compressed the data and reduced accuracy. Error bars were frequently missing or drawn incorrectly; they should represent the absolute uncertainty in the quantity plotted, not a generic small line. The line of best fit should pass through the centroid and, where possible, the origin, since s = 0 when t² = 0.
考官报告强调了图形绘制技能的不足。许多考生绘制了s对t（而非t²）的图，结果得到一条曲线，无法进行斜率分析。即使选择了正确的坐标轴，比例尺也常常不合适——例如，横轴使用1 cm = 0.01 s²，这压缩了数据并降低了精度。误差棒经常缺失或绘制错误；它们应表示所绘量的绝对不确定度，而非一条随便的小线段。最佳拟合线应通过所有点的质心，并在可能的情况下通过原点，因为当t² = 0时s = 0。
8. Gradient Calculation and Determination of g | 斜率计算与g的确定
Once the graph s vs. t² was drawn, the gradient m = Δs / Δ(t²) should be calculated using a large triangle, not individual data points. The value of g is then 2m. A common error was to forget the factor of 2, leading to a g value of around 4.9 m s⁻². Others calculated the gradient as Δt² / Δs, inverting the relationship. The unit of the gradient should be m s⁻², and the final g should be expressed with its absolute uncertainty, obtained from the difference between the steepest and shallowest acceptable lines of best fit.
绘制出s‑t²关系图后，应使用一个大三角形（而非单个数据点）来计算斜率m = Δs / Δ(t²)。g的值等于2m。一个常见错误是忘记了因子2，导致g值约为4.9 m s⁻²。有人计算斜率为Δt² / Δs，颠倒了关系。斜率的单位应该是m s⁻²，最终的g值应与其绝对不确定度一起表示，该不确定度由最佳拟合线的最大和最小可接受斜率之差得出。
9. Evaluation of Systematic vs. Random Errors | 系统误差与随机误差的评估
Candidates must distinguish between systematic and random uncertainties. In this free-fall experiment, systematic effects might include parallax error in reading the ruler, a misaligned light gate, or the assumption that initial velocity is zero if the ball is not truly dropped from rest. Random errors arise from variations in timing and small air currents. A top mark response linked specific error sources to the type of uncertainty and suggested practical ways to reduce them, such as using a plumb line to ensure vertical alignment or a vacuum column to remove air resistance.
考生必须区分系统误差和随机不确定度。在这个自由落体实验中，系统效应可能包括读取尺子时的视差、光门未对准，或者如果球并非真正由静止释放而假设初速度为零。随机误差源于计时波动和微小的气流。高分答案会将具体的误差来源与不确定度类型联系起来，并提出切实可行的减少方法，如使用铅垂线确保竖直对齐，或使用真空柱消除空气阻力。
10. Identifying and Handling Anomalies | 识别与处理异常值
The examiner report showed that few candidates correctly identified anomalous results in their dataset. An anomaly might be a time reading at a certain height that deviates significantly from the trend. Instead of simply removing it, candidates should first re-examine the procedure and, if possible, repeat that measurement. If the anomaly is retained, it must be clearly labelled on the graph but not included in the line of best fit. Understanding that anomalies can arise from a miss-timing or an obstruction during fall demonstrates higher-level evaluation.
考官报告显示，很少有考生能正确识别数据集中的异常值。异常值可能是某一高度的时间读数明显偏离趋势。考生不应简单删除它，而应首先重新检查操作过程，如有可能，应重复该测量。如果保留异常值，则必须在图上清晰标出，但不纳入最佳拟合线。理解异常值可能源于计时失误或下落中的阻滞，体现了更高层次的评估能力。
11. Suggestions for Improvement from the Examiner | 考官提出的改进建议
For a more reliable g value, candidates could suggest using electronic sensors such as light gates or a sound-triggered timer to remove reaction time, increasing the range of heights to at least 6 values between 0.50 m and 2.00 m, and using a slow-motion video analysis technique. The examiner also noted that stating ‘use more precise equipment’ without specifying what and why is insufficient. Practical modifications must be linked to a reduction in a specific uncertainty, e.g., a digital height gauge to reduce the absolute uncertainty in s to ±0.1 mm.
为了获得更可靠的g值，考生可以建议使用电子传感器，如光门或声控计时器，以消除反应时间，将高度范围增大到至少包含6个数值（0.50 m至2.00 m之间），并使用慢动作视频分析技术。考官还指出，仅仅说“使用更精确的设备”而不说明是什么和为什么，是不够的。实际的改进措施必须与减少某个特定不确定度联系起来，例如，使用数字高度计将s的绝对不确定度降至±0.1 mm。
12. Key Takeaways and Revision Tips | 关键要点与复习建议
Success in the PH02 practical investigation requires regular hands-on experience with data logging, graph plotting, and uncertainty analysis. Students should practise drawing error bars, determining extreme gradients, and using the formula for percentage uncertainty. It is equally important to read the instrument resolution correctly and to keep a thorough lab book. Revision must move beyond memorising procedures to understanding the physics behind each step. The examiner’s final advice was: ‘Show all working, pay attention to units, and never leave the evaluation section blank – even a brief comment on the largest source of uncertainty can earn marks.’
要在PH02实验探究中取得成功，需要经常动手实践数据记录、图表绘制和不确定度分析。学生应练习绘制误差棒、确定极端斜率，并使用百分不确定度的公式。同样重要的是，正确读取仪器分辨率并保留详细的实验记录本。复习必须超越记忆步骤，转而理解每一步背后的物理原理。考官的最终建议是：“展示所有计算过程，注意单位，决不要将评估部分留空——即使只对最大不确定度来源进行简短评论，也能得分。”
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