📚 A-Level Physics: June 2018 Paper 1 Experimental Investigation | A-Level 物理：2018年6月试卷1实验探究
In the June 2018 A‑Level Physics Paper 1, the experimental investigation question examined students’ ability to design, carry out, analyse and evaluate a practical task. This article breaks down the core skills assessed in that question and provides a step‑by‑step guide to mastering experimental investigations for A‑Level Physics.
在2018年6月A‑Level物理试卷1中，实验探究题考查了学生设计、实施、分析和评价实验的能力。本文分解了该题所评估的核心技能，并提供了掌握A‑Level物理实验探究的逐步指南。
1. Understanding the Experimental Context | 理解实验背景
The question typically describes a straightforward scenario, such as investigating the relationship between force and extension for a spring, or how the resistance of a wire varies with its length. The June 2018 paper presented a common practical: measuring the acceleration of free fall using a simple pendulum or an electromagnet‑release system. Candidates must extract the independent, dependent and control variables from the context. A clear grasp of the underlying physics – e.g. T = 2π√(L/g) – is essential for planning.
这类题目通常描述一个简单的场景，例如探究弹簧的力与伸长量的关系，或者导线电阻如何随长度变化。2018年6月的试卷呈现了一个常见的实验：使用单摆或电磁释放系统测量自由落体加速度。考生必须从背景中提取出自变量、因变量和控制变量。清晰掌握相关物理原理——例如 T = 2π√(L/g)——对设计实验至关重要。
2. Identifying and Controlling Variables | 识别与控制变量
Independent variable: length of the pendulum L. Dependent variable: period T. Controlled variables: mass of bob, amplitude (kept small, < 10°), release point. In the actual paper, students had to explain how to measure L from suspension point to centre of bob. The method must minimise parallax error by using a metre ruler aligned with a set square. Temperature and air currents were negligible if the amplitude was small.
自变量：摆长 L。因变量：周期 T。控制变量：摆球质量、振幅（保持微小，< 10°）、释放点。在实际试卷中，学生需要解释如何测量从悬挂点到摆球中心的长度 L。测量方法必须通过米尺配合三角尺对齐来减小视差。如果振幅微小，温度和气流影响可以忽略。
| Variable | 变量 | How to control | 如何控制 |
|---|---|
| Length L | 摆长 | Use a metre ruler and set square to mark start and end; measure from clamp to centre of bob. |
| Amplitude | 振幅 | Use a protractor to ensure release angle < 10°; keep same angle each trial. |
| Timer accuracy | 计时精度 | Use a light gate or measure time for 10 oscillations then divide by 10. |
This approach reduces systematic error. Timing multiple oscillations also minimises reaction‑time uncertainty.
这种方法可以减少系统误差。计时多个周期也能最小化反应时间引起的不确定度。
3. Designing a Results Table | 设计数据记录表
A good results table includes columns for the independent variable (L / m), dependent variable (time for 10 oscillations, t₁₀ / s), calculated period (T = t₁₀/10, s), and T² / s². Headings must show quantity and unit separated by a solidus or brackets, e.g. L / m. All raw data should be recorded to the same precision as the measuring instrument. For the metre ruler, this is usually ±0.001 m.
一个好的记录表应包含自变量（L / m）、因变量（10次振荡的时间 t₁₀ / s）、计算出的周期（T = t₁₀/10, s）以及 T² / s² 等列。表头必须用斜线或括号分开物理量和单位，如 L / m。所有原始数据的有效数字应与测量仪器精度保持一致。对于米尺，通常精确到 ±0.001 m。
| L / m | t₁₀ / s | T / s | T² / s² |
|---|---|---|---|
| 0.500 | 14.19 | 1.419 | 2.013 |
| 0.700 | 16.78 | 1.678 | 2.815 |
| 0.900 | 19.02 | 1.902 | 3.617 |
Repeating measurements and calculating a mean T reduces random error. The exam often asks how to present repeats and justify the number of significant figures.
重复测量并计算平均周期 T 可以减少随机误差。考试常会询问如何呈现重复数据以及如何确定有效数字的位数。
4. Dealing with Uncertainties | 处理不确定度
Every measurement has an uncertainty. For a metre ruler, the absolute uncertainty in a single reading is ± 0.001 m; for a length difference measured between two points, it becomes ± 0.002 m. For a stopwatch, the reaction‑time uncertainty is typically ± 0.2 s. When timing 10 oscillations, the absolute uncertainty in the period T is (0.2/10) = ± 0.02 s. Percentage uncertainties are calculated as (absolute uncertainty / value) × 100%. For T², the percentage uncertainty doubles because T is squared: %U(T²) = 2 × %U(T).
每个测量值都有不确定度。对于米尺，单次读数的绝对不确定度为 ± 0.001 m；对于两点间的长度差，不确定度为 ± 0.002 m。对于秒表，反应时间的不确定度通常为 ± 0.2 s。当测量10次振荡时，周期 T 的绝对不确定度为 (0.2/10) = ± 0.02 s。百分不确定度按 (绝对不确定度/测量值) × 100% 计算。对于 T²，由于平方关系，百分不确定度翻倍：%U(T²) = 2 × %U(T)。
In the June 2018 paper, candidates had to combine uncertainties to find the uncertainty in the calculated value of g. This requires careful propagation of errors through the equation g = 4π²L/T².
在2018年6月的试卷中，考生需要合成不确定度以求出计算值 g 的不确定度。这就需要通过方程 g = 4π²L/T² 谨慎地进行误差传递。
%U(g) = %U(L) + 2 × %U(T)
Thus the largest contribution to the uncertainty in g usually comes from the timing of T, especially if a stopwatch is used.
因此，g 的不确定度中最大的贡献通常来自 T 的计时，尤其在使用秒表时。
5. Graphical Analysis | 图像分析
The expected graph for the pendulum experiment is a plot of T² against L. According to T² = (4π²/g) L, the graph should be a straight line through the origin. The gradient m = 4π²/g, so g = 4π²/m. In Paper 1, students were asked to plot the data, draw a line of best fit, and determine g from the gradient. They also had to calculate the absolute uncertainty in the gradient by drawing worst‑fit lines (steepest and shallowest acceptable lines) that bracket the data points including error bars.
单摆实验预期的图像是 T² 对 L 作图。根据 T² = (4π²/g) L，图像应为一条过原点的直线。斜率 m = 4π²/g，因此 g = 4π²/m。在试卷1中，要求学生描点、画最佳拟合线，并从斜率求出 g。他们还需要通过画最陡和最浅的可接受线（包含误差棒的极端拟合线）来求出斜率的绝对不确定度。
Δm = (mmax − mmin) / 2
The percentage uncertainty in g is then the same as the percentage uncertainty in m, because g ∝ 1/m. Writing g with its absolute uncertainty (e.g. 9.81 ± 0.15 m s⁻²) and comparing with the accepted value (9.81 m s⁻²) completes the analysis.
g 的百分不确定度与 m 的百分不确定度相同，因为 g ∝ 1/m。将 g 与其绝对不确定度一起写出（如 9.81 ± 0.15 m s⁻²），并与标准值（9.81 m s⁻²）比较，即可完成分析。
6. Evaluation of the Experiment | 实验评价
Examiners expect a structured evaluation: comment on whether the results support the theoretical relationship, identify sources of uncertainty, and suggest realistic improvements. The main uncertainty in the pendulum experiment is measuring the period due to reaction time. A light gate connected to a data logger would eliminate this. Another issue is determining the exact centre of mass of the bob – using a bob with a clearly marked centre reduces this. The assumption that the string is massless and the bob is a point mass also introduces a slight systematic error.
考官期待结构化的评价：评论结果是否支持理论关系，指出不确定度的来源，并提出切实可行的改进方案。单摆实验的主要不确定度是由于反应时间引起的周期测量。使用连接数据采集器的光闸可以消除这个问题。另一个问题是确定摆球的准确质心——使用质心标记清晰的摆球可以减少此项误差。细绳无质量且摆球是质点的假设也会引入微小的系统误差。
For the June 2018 question, a common mark‑earning improvement was ‘measure time for 20 or more oscillations to reduce the percentage uncertainty in T, and use a fiducial marker at the equilibrium position for consistent timing.’
在2018年6月的题目中，一个常见的得分改进是“测量20次或更多次振荡的时间以减小 T 的百分不确定度，并在平衡位置使用基准标记以保证计时一致”。
7. Understanding the Aim of the Investigation | 理解探究目标
The experimental investigation is not just about getting the ‘right’ value of g. The mark scheme rewards logical planning, correct handling of data, valid graph work, and a critical evaluation. Even if a candidate’s g is far from 9.81, a clear, well‑supported method can still gain high marks. Paper 1 reflects this emphasis on the process of science rather than only the outcome.
实验探究的目的不仅仅是获得 g 的“正确”数值。评分方案奖励合乎逻辑的计划、正确的数据处理、有效的作图工作以及批判性评价。即使考生的 g 与 9.81 相差甚远，只要方法清晰、有据可依，仍然可以获得高分。试卷1正反映了这种对科学过程而非仅仅关注结果的重视。
8. Common Mistakes in Experimental Questions | 实验题的常见错误
One mistake is confusing precision with accuracy. A reading can be very precise (many decimal places) but completely inaccurate due to a systematic error. Another is failing to convert units, e.g. plotting L in cm when the equation expects metres. Not including error bars on the graph, or drawing a line of best fit that does not pass through all error bars, loses marks. Also, some candidates forget to calculate T² or use the wrong formula for the period.
常见错误之一是混淆了精密度和准确度。一个读数可能非常精密（许多小数位），但会因系统误差而完全不准确。另一个错误是未换算单位，例如当方程预期以米为单位时，L 却用厘米作图。图上未画误差棒，或最佳拟合线没有穿过所有误差棒，都会丢分。此外，一些考生忘记计算 T² 或者使用了错误的周期公式。
9. Tackling the Question Under Time Pressure | 在时间压力下应对试题
In a 1.5‑hour paper, the experimental question is often worth 12–15 marks and should take about 20 minutes. Begin by scanning the whole question to understand the equipment list and the variables. Plan your answer mentally: design, data, graph, evaluation. Often the question is structured in parts (a)–(e), which guide you through the process. Stick to the bullet points asked; do not write an essay but ensure you cover each instruction. For calculation parts, show all steps and give the final answer to an appropriate number of significant figures (usually 3 s.f.).
在1.5小时的试卷中，实验题通常占12–15分，应花费约20分钟。开始时先浏览整个题目，了解设备清单和变量。在脑中计划答案：设计、数据、图像、评价。题目通常分解为(a)到(e)等部分，引导你完成整个过程。紧扣题目要求回答；不要写成论文，但要确保覆盖每条指令。对于计算部分，展示所有步骤，并给出合适有效数字（通常是3位）的最终答案。
10. Linking to Other Core Practicals | 联系其他核心实验
The skills tested in the June 2018 pendulum investigation are transferable to all A‑Level core practicals. Whether measuring the resistivity of a wire (R = ρL/A), the Young modulus of a material (stress/strain), or the internal resistance of a cell (V = ε − Ir), the logic is identical: identify variables, linearise the equation, measure with repetitions, plot the appropriate graph, extract the gradient, calculate the target quantity, propagate uncertainties, and critically evaluate. Mastering one practical deeply is the key to performing well on any experimental question.
2018年6月单摆实验所考查的技能可迁移至所有A‑Level核心实验。无论是测量导线电阻率（R = ρL/A）、材料的杨氏模量（应力/应变）还是电池内阻（V = ε − Ir），其逻辑完全相同：识别变量、线性化方程、重复测量、作出相应图像、提取斜率、求出目标量、传递不确定度并进行批判性评价。深入掌握一个实验是在任何实验题上表现优异的关键。
11. Preparing for Your Own Exam | 为你的考试做准备
To excel, practise past paper experimental questions under timed conditions. Learn the standard uncertainty propagation rules and practise drawing error bars and worst‑fit lines on graph paper. Familiarise yourself with typical improvements: use of data loggers, repeating measurements, reducing parallax, and controlling environmental factors. The June 2018 paper serves as a perfect model for the depth and style of A‑Level practical assessment.
为了脱颖而出，请在限时条件下练习历年真题中的实验题。掌握标准的不确定度传递规则，并在坐标纸上练习绘制误差棒和最差拟合线。熟悉典型的改进措施：使用数据采集器、重复测量、减小视差以及控制环境因素。2018年6月的试卷为A‑Level实验评估的深度和风格提供了完美的范例。
12. Conclusion | 结语
The experimental investigation question in A‑Level Physics June 2018 Paper 1 assessed a full range of practical competencies. By following a systematic approach – understand, design, measure, graph, calculate, evaluate – you can secure high marks. Remember that the process matters as much as the final value. With thorough preparation, any experimental scenario becomes manageable.
A‑Level物理2018年6月试卷1中的实验探究题全面评估了各项实验能力。遵循系统的步骤——理解、设计、测量、作图、计算、评价——你就能稳拿高分。请记住，过程与最终结果同样重要。通过充分准备，任何实验场景都将变得迎刃而解。
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