📚 AS Physics Unit 1 Experimental Investigation: Jan 2020 Paper Insights | AS物理单元1实验探究：2020年1月试卷深度解析
Experimental investigation questions form the backbone of AS Physics Unit 1. They test your ability to design experiments, collect data, handle uncertainties, and draw valid conclusions. The January 2020 paper is a classic example where the experimental scenario demanded careful consideration of variables, measurement techniques, and error propagation. This article breaks down the core skills required, using insights from that paper to guide you through typical investigation tasks.
实验探究题是AS物理单元1的核心。它们考查你设计实验、收集数据、处理不确定度以及得出有效结论的能力。2020年1月的试卷就是一个经典案例，实验情境要求你仔细考量变量、测量技术和误差传递。本文将通过该试卷的洞察，拆解所需的核心技能，带你掌握典型的探究任务。
1. Decoding the Experiment Statement | 解读实验陈述
In the Jan 2020 paper, candidates first encountered a clear aim, often something like “investigate how the extension of a spring depends on the applied force”. Your immediate task is to rephrase that aim in terms of independent and dependent variables. Read every word: words such as “investigate”, “determine”, or “measure” signal different requirements. Determine usually asks for a specific physical quantity, while investigate implies you need to find a relationship.
在2020年1月试卷中，考生首先会看到一个明确的实验目的，比如“探究弹簧的伸长量如何随施加的力变化”。你的首要任务是用自变量和因变量来重新表述这个目标。仔细阅读每一个词：“探究”、“测定”或“测量”等词语暗示着不同的要求。“测定”通常要求找出一个具体的物理量，而“探究”意味着你需要找到一种关系。
Often the statement will hint at the apparatus available, such as a ruler, slotted masses, a stand, and a spring. Your role is to plan how to use them effectively. Even before you plan, identify the key physical principle, e.g., Hooke’s Law. In the 2020 context, the law was the basis for determining the spring constant or testing elasticity.
陈述通常会暗示可用的仪器，比如尺子、槽码、铁架台和弹簧。你的任务是规划如何有效使用它们。甚至在规划之前，就要识别出关键的物理原理，例如胡克定律。在2020年的情境中，该定律是测定弹簧劲度系数或测试弹性的基础。
2. Identifying Variables Clearly | 明确识别变量
The independent variable is the one you deliberately change. In a spring investigation from Jan 2020, it would be the force applied (calculated from mass × gravitational field strength). The dependent variable is the extension of the spring, measured as the change in length. Control variables must be kept constant: temperature (to avoid affecting spring stiffness), the same spring (material, dimensions), and the initial point of measurement.
自变量是你故意改变的物理量。在2020年1月的弹簧探究中，它就是施加的力（由质量 × 重力场强度计算得出）。因变量是弹簧的伸长量，即长度变化。控制变量必须保持不变：温度（避免影响弹簧刚度）、同一根弹簧（材料、尺寸）以及测量的起始点。
Marks in the paper are often awarded for stating how each variable is measured or controlled. For instance: “The independent variable is the force, varied by adding known masses and calculating F = mg, where g is taken as 9.81 N kg⁻¹.” You must also mention the range: e.g., 0 – 2 N in steps of 0.2 N. Six to ten readings are expected.
试卷中通常会给分给写明每个变量如何测量或控制的做法。例如：“自变量是力，通过添加已知质量并计算 F = mg 来改变，其中 g 取 9.81 N kg⁻¹。” 你还需提及范围：比如 0–2 N，以 0.2 N 为增量。通常需要六到十个读数。
3. Apparatus Selection and Resolution | 仪器选择与分辨率
Typical apparatus in the Jan 2020 setup included a metre rule, a set of slotted masses, a clamp stand, and a spring. The metre rule has a resolution of ±1 mm, but your uncertainty in reading extension is likely larger due to parallax and judging the spring’s end. You might use a set-square to align the eye horizontally. For force, the smallest mass may be 10 g, giving a resolution of 0.1 N.
2020年1月实验装置中典型的仪器包括米尺、一套槽码、铁架台和弹簧。米尺的分辨率为 ±1 mm，但在读取伸长量时，由于视差和判断弹簧端点，不确定度通常更大。你可以用三角尺来水平对齐视线。对于力，最小质量可能是 10 g，提供 0.1 N 的分辨率。
Always justify why you chose a particular instrument. For length, a vernier calliper may seem better, but it cannot measure the spring’s total length of 20+ cm. The metre rule is more practical. When asked to improve precision, you might suggest using a digital force sensor or a pointer and scale aligned behind the spring. Such improvements were assessed in Jan 2020.
始终要说明你为何选择某个特定仪器。对于长度，游标卡尺看似更佳，但它无法测量弹簧超过20厘米的总长。米尺更实用。当被要求提高精度时，你可能建议使用数字力传感器，或在弹簧后面安装指针和刻度尺。这些改进在2020年1月试卷中有所考查。
4. Risk Assessment and Safety | 风险评估与安全
Although not a major mark earner in Jan 2020, a brief safety comment is good practice. For a hanging spring and masses, the risk is masses falling on feet or the spring snapping. Low risk, but you can mention: “Place a soft mat or tray below the masses; wear safety shoes; ensure the clamp is secure.” Always link the hazard to the experiment.
虽然在2020年1月的试卷中安全评估并非主要得分点，但简短提及是个好习惯。对于悬挂的弹簧和砝码，风险是砝码掉落砸到脚或弹簧断裂。风险较低，但你可以提：“在砝码下方放置软垫或托盘；穿安全鞋；确保夹子牢固。” 始终将危险与实验联系起来。
If using a free-fall apparatus to measure g (another possible Unit 1 experiment), mention avoiding obstruction and ensuring a clear landing area. Keep safety points realistic and concise.
如果使用自由落体装置测量 g（另一种可能的单元1实验），要提及避免障碍物并确保有清晰的着地区域。安全要点要切合实际且简洁。
5. Data Collection Strategy | 数据收集策略
For the Jan 2020 spring experiment, you would first measure the unloaded length of the spring, L₀, using the metre rule. Then add masses one by one, measuring the new length L. Repeat each measurement two or three times to reduce random error and take an average. Record masses, total force, length L, and calculate extension x = L – L₀.
对于2020年1月的弹簧实验，你会首先用米尺测量弹簧的空载长度 L₀。然后逐一添加质量，测量新的长度 L。每个读数重复两到三次以减少随机误差并取平均值。记录质量、总力、长度 L，并计算伸长量 x = L – L₀。
The Jan 2020 paper often provided a table for you to complete. You must fill it with consistent significant figures and units. For extension, if L₀ was measured to the nearest 1 mm, extension should be given to the nearest millimetre. The calculated force might have 2 or 3 significant figures based on the mass values. Always leave units in the header row of the table.
2020年1月试卷通常会提供一个表格让你填写。你必须用一致的有效数字和单位来填写。对于伸长量，如果 L₀ 精确到毫米，伸长量也应精确到毫米。计算力时，根据质量值的有效数字，保持2或3位有效数字。始终在表头行标注单位。
6. Plotting and Analysing Graphs | 绘图与图像分析
A graph of force F against extension x (or vice versa) is expected. Jan 2020 likely asked you to plot a graph and determine the spring constant k. Since F = kx, the gradient of an F‑x graph equals k. If you plotted x on the y-axis and F on the x-axis, the gradient would be 1/k. Always label axes with quantity and unit, use sensible scales, and draw a best-fit line.
预计你会绘制力 F 与伸长量 x 的关系图（或反之）。2020年1月试卷很可能要求你绘制图像并测定弹簧劲度系数 k。因为 F = kx，所以 F‑x 图像的斜率等于 k。如果你将 x 画在 y 轴，F 画在 x 轴，斜率则是 1/k。始终用物理量和单位标注坐标轴，使用合理的比例，并画出最佳拟合线。
The Jan 2020 mark scheme rewarded accurate plotting, a line that passed through the origin (if Hooke’s law is valid), and calculation of gradient using a large triangle. You must show the triangle on the graph and give the gradient to 2 or 3 significant figures. The unit of k derived from such a graph is N m⁻¹.
2020年1月的评分方案奖励精确的描点、一条通过原点的直线（若胡克定律成立），以及使用大三角形计算斜率。你必须在图像上画出三角形，并将斜率以2或3位有效数字给出。从该图像得出的 k 的单位是 N m⁻¹。
7. Handling Uncertainties from Graphs | 从图像处理不确定度
One of the key exam skills tested in Jan 2020 was uncertainty analysis. To find the uncertainty in the gradient, draw two lines: the steepest and shallowest plausible lines through the error bars (or through the points if error bars are not given). Calculate both gradients, then uncertainty = (max gradient – min gradient)/2.
2020年1月试卷考查的关键应试技能之一是不确定度分析。要找出斜率的不确定度，需画出两条线：通过误差棒（或如果没有误差棒则通过数据点）的“最陡”和“最平”合理直线。计算两个斜率，然后不确定度 = (最大斜率 – 最小斜率)/2。
The Jan 2020 paper often provided pre-calculated percentage uncertainties for you to combine. For instance, if k is derived from a single gradient and other measured quantities, you might need to combine percentage uncertainties using the rules: add for multiplication/division. This approach was often tested in the data analysis section.
2020年1月试卷常提供预先计算好的百分比不确定度让你组合。例如，若 k 是由单一斜率和其他测定量导出，你可能需要运用合成规则：乘除时相加百分比不确定度。这种方法在数据分析部分经常考查。
8. Error Sources and Evaluation | 误差来源与评估
Systematic error in the Jan 2020 spring experiment might be a zero error in the ruler, or the spring having a coiled end that makes it difficult to define the exact point of measurement. This could shift all readings by a constant amount but not affect the gradient. Random errors arise from judgement of the spring end, parallax, and mass variation.
2020年1月弹簧实验中的系统误差可能是尺子的零误差，或者弹簧的盘簧末端导致难以确定精确测量点。这可能会使所有读数偏移一个恒定值，但不影响斜率。随机误差来源于对弹簧端点的判断、视差以及砝码质量的差异。
When evaluating the experiment, you could comment on the largest source of uncertainty: “The extension is small for the first few masses, meaning the percentage uncertainty in x is large. This could be reduced by using a pointer and a vernier scale, or a motion sensor.” Such improvements were commonly asked in Jan 2020 papers.
评估实验时，你可以评论最大的不确定度来源：“前几个质量对应的伸长量较小，这意味着 x 的百分比不确定度很大。这可以通过使用指针和游标尺，或运动传感器来减小。” 这类改进方案在2020年1月试卷中经常被问到。
9. Determining Physical Constants Accurately | 准确测定物理常数
If the aim was to determine the spring constant k, the Jan 2020 paper expected you to not just give the gradient, but also state it with its absolute uncertainty and unit: e.g., k = 25.4 ± 0.6 N m⁻¹. You might be asked to compare your value with a known value and discuss validity. For example, “Our value of 25.4 N m⁻¹ differs from the expected 24.8 N m⁻¹ by 2.4%, which lies within the experimental uncertainty, hence it is consistent.”
如果目的是测定弹簧劲度系数 k，2020年1月试卷期望你不仅给出斜率，还要注明其绝对不确定度和单位：例如 k = 25.4 ± 0.6 N m⁻¹。你可能还会被要求将你的值与已知值比较并讨论有效性。例如：“我们的值25.4 N m⁻¹与预期值24.8 N m⁻¹相差2.4%，这在实验不确定度范围内，因此两者一致。”
The paper often gave a target constant like Young’s modulus from a wire extension experiment. Knowing how to compute percentage difference and compare it with percentage uncertainty is vital. In Jan 2020, candidates who could correctly argue that the difference was larger than the instrumental uncertainty concluded the presence of a procedural error.
试卷常给出目标常数，比如金属丝伸长实验中的杨氏模量。懂得如何计算百分比差值并与百分比不确定度比较至关重要。在2020年1月的试卷中，能够正确论证差值大于仪器不确定度的考生，得出的结论是存在操作误差。
10. Applying to Other Unit 1 Investigations | 应用到其他单元1探究
The skills from the Jan 2020 paper are directly transferable to other common Unit 1 experiments: measuring g using free fall or a pendulum, determining the Young modulus of a wire, investigating terminal velocity in a fluid, or resistors in series/parallel in the electricity topic. In each case, the logical flow of variables → apparatus → data → graph → uncertainty remains the same.
2020年1月试卷中的技能可直接应用于其他常见的单元1实验：用自由落体或单摆测量 g、测定金属丝的杨氏模量、探究流体中的终极速度，或电学主题中的电阻串联/并联。在每种情况下，变量→仪器→数据→图像→不确定度的逻辑流程保持不变。
For instance, in the Young modulus experiment, the independent variable is force (masses), the dependent is extension (measured with a vernier or a travelling microscope), and control variables are length, cross-sectional area, and temperature. The gradient of a stress‑strain graph yields the Young modulus. Similar graph‑based analysis of uncertainty is required.
例如，在杨氏模量实验中，自变量是力（砝码），因变量是伸长量（用游标或移测显微镜测量），控制变量是长度、横截面积和温度。应力‑应变图像的斜率给出杨氏模量。同样需要进行基于图像的不确定度分析。
11. Common Mistakes and How to Avoid Them | 常见错误与避免方法
From examiner reports on the Jan 2020 paper, frequent errors included mixing up the axes, not starting the graph origin at (0,0) when the relationship passes through zero, using too small a triangle for gradient, forgetting units in final answers, and treating percentage uncertainty as a simple subtraction rather than addition for combined quantities. Also, describing improvements without linking to the error.
根据2020年1月试卷的考官报告，常见错误包括混淆坐标轴、当关系通过零点时却不从(0,0)开始绘图、用于计算斜率的三角形太小、最终答案遗漏单位，以及在合成物理量时将百分比不确定度当作简单相减而非相加。还有，描述改进措施时未能与误差关联。
To avoid these, always annotate your graph with “force F / N” and “extension x / mm”. For a spring, the extension is zero when force is zero, so force the line through the origin if appropriate, but only if the question says the spring obeys Hooke’s law. For the triangle, use at least half the graph’s span.
为避免这些错误，始终在图像上标注“力 F / N”和“伸长量 x / mm”。对于弹簧，当力为零时伸长量为零，因此如果合适的话应强制让直线通过原点，但仅限于题目说弹簧遵守胡克定律的情况。选取三角形时，至少要使用图像跨度的一半。
12. Summary: Mastering Unit 1 Experiment Questions | 总结：掌握单元1实验题
The Jan 2020 AS Physics Unit 1 experimental investigation is not just about performing a practical; it assesses your holistic understanding of measurement and data evaluation. By systematically identifying variables, selecting appropriate instruments, tabulating data with correct uncertainties, plotting a precise graph, calculating gradient and its uncertainty, and finally linking the result to theory, you can secure high marks.
2020年1月AS物理单元1的实验探究不仅仅是动手操作；它评估的是你对测量和数据分析的全面理解。通过系统地识别变量、选择合适仪器、以正确的不确定度列表记录数据、绘制精确图像、计算斜率及其不确定度，并最终将结果与理论联系起来，你就能获得高分。
Remember that each mark in the paper targets a specific skill: a mark for the correct variable, a mark for the graph scales, a mark for the gradient calculation, and a mark for the evaluation. Treat every sub-question as an opportunity to demonstrate your precision and depth of thought. Practice with past papers like Jan 2020, and you will find the pattern repetitive and manageable.
请记住，试卷中的每一分都指向一个特定技能：变量正确得一分，图像比例得一分，斜率计算得一分，评估得一分。把每个小问都当作展示你精准度和思维深度的机会。用像2020年1月这样的历年真题进行练习，你就会发现其中的模式是重复且可控的。
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