📚 A-Level Physics June 18 Paper 3 Mark Scheme: Experimental Investigation Skills | A-Level 物理 2018年6月卷三评分标准：实验探究核心技能
Understanding the mark scheme for A-Level Physics Paper 3 is not just about knowing what earns marks — it reveals exactly how examiners assess your ability to think like a scientist. The June 2018 Paper 3 mark scheme highlights key skills in experimental design, data collection, uncertainty analysis and critical evaluation. This article breaks down those expectations into clear, actionable strategies so you can approach any investigation with confidence and precision.
理解 A-Level 物理第三卷的评分标准，不仅仅是知道怎样拿到分数——它揭示了考官如何评估你像科学家一样思考的能力。2018 年 6 月第三卷的评分标准突出了实验设计、数据收集、不确定度分析和批判性评估等关键技能。本文将把这些要求拆解成清晰、可操作的策略，帮助你自信而准确地应对任何实验探究。
1. Defining Variables Clearly | 清晰定义变量
The mark scheme consistently rewards candidates who distinguish between independent, dependent and control variables early in their plan. The independent variable is the one you deliberately change; the dependent variable is what you measure as a result; control variables are the quantities you keep constant to ensure a fair test.
评分标准始终青睐那些在实验计划中一开始就清晰区分自变量、因变量和控制变量的考生。自变量是你有意改变的量；因变量是你因此测量的量；控制变量则是你为保持公平测试而维持恒定的量。
For example, when investigating how the length of a pendulum affects its period, the length is independent, the period is dependent, and the mass of the bob and the amplitude of swing should be controlled. The 2018 paper expects you to state these explicitly and, where possible, explain how you would control each variable.
例如，在探究摆长如何影响周期时，摆长是自变量，周期是因变量，摆锤质量和摆幅角度应当被控制。2018 年的试卷希望你明确陈述这些变量，并在可能的情况下说明如何控制每一个变量。
2. Selecting Apparatus with Appropriate Precision | 选择精度恰当的仪器
A recurring theme in the June 18 Paper 3 mark scheme is the link between the apparatus chosen and the justified precision needed. Merit is given for naming instruments with appropriate ranges and resolutions — a micrometer screw gauge rather than a ruler for a wire’s diameter, or a stopwatch reading to 0.01 s for timing oscillations.
2018 年 6 月卷三评分标准中反复出现的一个主题是所选仪器与所需合理精度之间的联系。如果考生能说出具有合适量程和分辨率的具体仪器名称——测量金属丝直径用千分尺而不是直尺、计时振荡用可读到 0.01 秒的秒表——就能获得相应分数。
Always justify your choice. Saying ‘use a digital calliper because it has a higher resolution (0.01 mm) than a ruler (1 mm)’ shows evaluative thinking that examiners look for. Avoid vague phrases like ‘use a ruler’ without stating its resolution or the quantity being measured.
一定要为你的选择提供理由。像“使用数字游标卡尺，因为其分辨率（0.01 毫米）高于直尺（1 毫米）”这样的表达，体现了考官所寻求的评判性思维。避免使用“用尺子量”这样模糊的表述，而不说明它的分辨率或所要测量的量。
3. Designing a Repeatable Procedure | 设计可重复的操作步骤
The mark scheme insists on a logical, step-by-step sequence that another person could follow. Instructions such as ‘Set up the circuit as shown in the diagram’ or ‘Record the time for 10 complete oscillations and divide by 10 to find the period’ are good but must be complete — mentioning how to vary the independent variable and record the dependent variable.
评分标准要求呈现一个具有逻辑性、逐步推进的操作序列，并且另一个人也能照着操作。像“如图所示搭建电路”或“记录 10 个完整振荡的时间并除以 10 以求得周期”这类说明很好，但必须完整——要提到如何改变自变量并记录因变量。
Include details of repetition. The June 18 mark scheme specifically credits ‘repeat measurements and calculate a mean’ to reduce random error. For any experiment, state how many readings you will take (at least six for a graph) and that you will repeat each one, say, three times.
要包含重复测量的细节。2018 年 6 月的评分标准明确给“重复测量并计算平均值”以降低随机误差加分。对于任何实验，要说明你将会取多少组读数（作图至少需要六组），以及每组读数你将重复测量，比如三次。
4. Constructing an Effective Data Table | 构建有效的数据表格
A well-designed results table immediately signals a methodical approach. The mark scheme from June 18 expects columns with headings that include both the quantity and its unit, separated by a solidus (/) or bracket, such as ‘Length L / cm’ or ‘Time for 10T / s’. Consistent decimal places matching the instrument’s precision are essential.
一张设计良好的结果表格能立刻显示出有条不紊的实验素养。2018 年 6 月的评分标准要求表格各栏的标题应同时包含物理量及其单位，用斜线（/）或括号分隔，例如“长度 L / cm”或“10T 时间 / s”。保持与仪器精度相匹配的小数位数至关重要。
Do not forget to include columns for calculated quantities such as ‘Period T / s’ or ‘T² / s²’. The mark scheme often awards a specific mark for a correctly calculated derived quantity, so organise your table to show raw data first, then processed data.
不要忘记添加计算量栏目，例如“周期 T / s”或“T² / s²”。评分标准常常会为正确计算的导出量给一个特定的分数，因此设计表格时应先列出原始数据，再列出处理后的数据。
5. Handling Raw and Derived Uncertainties | 处理原始与导出量的不确定度
A significant portion of Paper 3 marks revolves around uncertainty. From the June 18 mark scheme, you need to state the absolute uncertainty in each raw reading, often ± half the smallest scale division for analogue instruments, or ± the last stable digit for digital ones. For repeated readings, the half-range (±(max − min)/2) is commonly accepted.
第三卷有相当可观的分数与不确定度有关。根据 2018 年 6 月的评分标准，你需要给出每个原始读数的绝对不确定度。对于模拟式仪器，通常是 ± 最小刻度的一半；对于数字式仪器，则是 ± 最末稳定位。对重复读数而言，半范围（±(最大值 − 最小值)/2）是常用的表示方法。
When quantities are combined, you must propagate uncertainties correctly. If T = t/10, the absolute uncertainty in T is the absolute uncertainty in t divided by 10. The mark scheme gives credit for showing working, even if the arithmetic is slightly off, as long as the principle is clear.
当多个量组合时，你必须正确传递不确定度。若 T = t/10，T 的绝对不确定度就是 t 的绝对不确定度除以 10。评分标准对于展示计算过程的情况会给予肯定，即使最终算数略有偏差，只要原理清晰即可。
6. Plotting Graphs that Earn Full Marks | 绘制能拿到满分的图表
The graph is often worth 4–6 marks in Paper 3. To satisfy the June 18 mark scheme, axes must be labelled with quantity and unit, scales must be linear and use more than half the grid, and points must be plotted as neat crosses or small circles with a sharp pencil. A misleading scale (e.g. awkward multiples of 3) will lose marks.
第三卷中图表通常值 4–6 分。要满足 2018 年 6 月的评分标准，坐标轴必须标注物理量和单位，刻度必须线性并利用超过半幅方格纸，数据点必须用削尖的铅笔画成整洁的叉号或小圆圈。使用不方便的刻度（例如 3 的奇数倍）会导致失分。
The best-fit line must be a smooth straight line that passes as closely as possible to the points, with a balanced distribution of points above and below it. The mark scheme looks for a thin, continuous line drawn with a transparent ruler, not a thick fuzzy line. If the relationship is curved, draw a smooth curve without ruling.
最佳拟合线必须是一条平滑的直线，尽可能贴近所有数据点，且线上方和下方的点数分布均衡。评分标准要求用透明尺子画出细而连续的直线，而非粗而模糊的线。如果关系是曲线的，要画出光滑曲线，不用尺子硬画。
7. Determining Gradient and Intercept Precisely | 精确求取斜率与截距
The June 18 mark scheme rewards candidates who use a large triangle to find the gradient — the triangle should span at least half the length of the drawn line. Read off coordinates from the line itself, not from data points. Show the calculation clearly: gradient = (y₂ − y₁) / (x₂ − x₁).
2018 年 6 月的评分标准对使用大三角形求取斜率的考生给予加分——该三角形的边长至少应跨越所画直线长度的一半。从拟合线上读取坐标，而非从数据点读取。要清晰地展示计算过程：斜率 = (y₂ − y₁) / (x₂ − x₁)。
For the intercept, when the x-axis starts at zero, read directly off the graph. If the x-axis does not start at zero, use y = mx + c with a point on the line to calculate c. Always quote the final gradient and intercept with appropriate units and to a sensible number of significant figures (usually 2 or 3).
求截距时，若 x 轴从零开始，可直接从图上读取。若 x 轴不是从零开始，可利用直线上的一个点和公式 y = mx + c 来计算 c。最终的斜率和截距应始终带上适当的单位，并保留合理的有效数字位数（通常为 2 或 3 位）。
8. Relating Results to Equations and Constants | 将结果与方程和常量关联
In many Paper 3 experiments, the gradient or intercept corresponds to a physical constant such as g, resistivity, or Young modulus. The mark scheme requires you to state clearly what the gradient represents, e.g. ‘gradient = 4π²/g’ for a pendulum, and then equate it to your measured value to find the constant.
在许多第三卷实验中，斜率或截距对应于某一物理常量，如 g、电阻率或杨氏模量。评分标准要求你明确陈述斜率代表了什么，例如对于单摆“斜率 = 4π²/g”，然后将其与你测得的数值建立等式以求出该常量。
When comparing with a known value, calculate the percentage difference or percentage uncertainty. The June 18 mark scheme often asked whether the accepted value lies within the experiment’s uncertainty range, and the ability to make this judgement is highly rewarded.
与已知值比较时，要计算百分差或百分不确定度。2018 年 6 月的评分标准常常要求判断公认值是否落在实验的不确定度范围内，而这种判断能力会得到高度认可。
9. Identifying Sources of Uncertainty and Error | 辨识不确定度来源与误差
A common pitfall is to list vague errors like ‘human error’ or ‘parallax error’ without linking them to the specific measurement. The mark scheme wants you to state exactly which measurement is affected and whether the error is random or systematic.
一个常见的失误是罗列诸如“人为误差”或“视差误差”这类笼统说法，却不将它们与具体的测量联系起来。评分标准希望你能确切指出哪个测量受到了影响，以及该误差是偶然误差还是系统误差。
For a pendulum, a random error could be the variation in reaction time when starting and stopping the stopwatch. A systematic error could be a ruler with a zero error or a meter stick that is not perpendicular to the pivot. Linking cause and effect earns the analysis marks.
对于单摆，偶然误差可能来自启动和停止秒表时反应时间的差异。系统误差可能来自直尺存在零刻度误差或米尺没有与支点垂直。将原因与影响联系起来分析，才能拿到分析评价分数。
10. Proposing Specific and Feasible Improvements | 提出具体且可行的改进方法
A question that asks for two improvements appears in almost every Paper 3. According to the June 18 mark scheme, each suggestion must be linked to a previously identified problem, and it must be practical within a school laboratory. Generic statements like ‘use a computer’ are rarely credited.
几乎每一份第三卷都会有一道要求提出两项改进的问题。根据 2018 年 6 月的评分标准，每条建议都必须与之前指出的某个问题相关联，且必须在学校实验室中切实可行。“用电脑”这类泛泛而谈的说法极少得分。
Good examples include: ‘Use a fiducial marker at the centre of oscillation to improve timing precision’ or ‘Measure the diameter of the wire in three places using a micrometer to take an average and reduce the effect of irregular thickness’. These improvements directly address a source of uncertainty.
好的例子包括：“在振荡中心设置一个参照标记，以提高计时精度”或“用千分尺在金属丝的三个不同位置测量直径，取平均值以减少厚度不均匀的影响”。这些改进直接针对了不确定度的来源。
11. Understanding Risk Assessment and Safety | 理解风险评估与安全措施
Although less heavily weighted, safety considerations are part of the planning process the mark scheme rewards. Mention potential hazards (e.g. hot wires, falling masses, stretched springs) and simple precautions (e.g. wear goggles, use a low voltage, place a cushion on the floor).
虽然权重较小，但安全考量是实验规划的一部分，评分标准同样会给予加分。要提及潜在的危害（如发烫的导线、下落的砝码、拉伸的弹簧）以及简单的预防措施（如佩戴护目镜、使用低电压、在地板放置软垫）。
Do not invent exotic dangers — the exam expects common sense. For electrical circuits, note that currents should be switched off between readings to prevent heating. For a loaded spring, mention the importance of securing the clamp stand to avoid tipping.
不要凭空编造离奇的危险——考试考查的是常识。对于电路，要指出在两次读数之间应断开电流以防导线发热。对于载重的弹簧，要说明固定好铁架台以防倾倒的重要性。
12. Mastering the Conclusion and Justification | 掌握结论与论证的写法
The final few lines of your answer should directly address the aim, state whether the relationship is proportional or inversely proportional, and quote supporting data. From the June 18 mark scheme, a conclusion that says ‘the period squared is directly proportional to the length because the graph is a straight line through the origin’ is ideal.
答案的最后几行应直接回扣实验目的，说明关系是正比还是反比，并引用支持数据。根据 2018 年 6 月的评分标准，像“周期的平方与摆长成正比，因为图表是一条通过原点的直线”这样的结论就是理想答案。
Always quantify your judgement. Instead of ‘the value is close to the accepted value’, write ‘the experimental value of g = 9.6 ± 0.3 m s⁻², which agrees with the accepted value 9.81 m s⁻² within experimental uncertainty’. This final touch demonstrates full command of the skills the Paper 3 mark scheme assesses.
总要量化你的判断。与其说“该值与公认值接近”，不如写“实验值 g = 9.6 ± 0.3 m s⁻²，在实验不确定度范围内与公认值 9.81 m s⁻² 相符”。这一收尾体现了你对第三卷评分标准所考察的各项技能已完全掌握。
Published by TutorHao | Physics Revision Series | aleveler.com
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