📚 Pre-U OCR Physics: Key Points for Experimental/Practical Assessments | Pre-U OCR 物理：实验/实践考核要点
Success in OCR Pre-U Physics hinges not only on theoretical knowledge but also on the mastery of practical skills. The specification assesses these through a unique combination of a written practical exam and an independent research project. This article distills the key points you must grasp to excel in experimental work, from planning and measurement to uncertainty analysis and the personal investigation.
在 OCR Pre-U 物理中取得优异成绩，不仅取决于理论知识，还取决于对实践技能的掌握。该大纲通过书面实践考试与独立研究项目的独特组合来评估这些技能。本文提炼了你在实验工作中必须掌握的关键要点，从计划、测量到不确定度分析和个人调查。
1. Overview of Practical Assessment in Pre-U Physics | Pre-U 物理实践评估概览
Practical skills in OCR Pre-U Physics are formally examined in two components. Component 03 (Practical Skills in Physics) is a 1 hour 30 minutes written paper in which you answer questions based on pre-released experimental scenarios and data sets. This paper tests your ability to plan, analyse, and evaluate without carrying out hands-on experiments during the examination.
OCR Pre-U 物理的实践技能在两个组件中正式考查。组件 03（物理实践技能）是一份 1 小时 30 分钟的书面试卷，你需根据预先公布的实验场景和数据集回答问题。该试卷考察你在不动手实验的情况下进行计划、分析和评估的能力。
Component 04 (Personal Investigation) is a substantial independent research project performed under supervision. You choose a topic, design and perform the investigation, process the data, and write a full scientific report. This component carries significant weight and distinguishes Pre-U from many other qualifications.
组件 04（个人调查）是在督导下完成的一个大型独立研究项目。你自行选题，设计并实施调查，处理数据，并撰写完整的科学报告。该组件权重很大，使 Pre-U 课程有别于许多其他资格考试。
2. Planning and Design | 计划与设计
A well-structured plan is the foundation of any reliable experiment. Start by clearly phrasing the aim and the hypothesis you intend to test. Distinguish between the independent variable (what you change), the dependent variable (what you measure), and control variables (factors kept constant). List all apparatus with quantities and ranges, and draw a labelled diagram.
结构良好的计划是一切可靠实验的基础。先要清楚地表述实验目的和你要检验的假设。区分自变量（你改变的）、因变量（你测量的）和控制变量（保持不变的因素）。列出所有仪器及其数量和量程，并绘制带标注的示意图。
Your method must include specific steps to minimise systematic errors, such as checking the zero error on a micrometer or calibrating a thermometer at 0 °C and 100 °C. Indicate how you will obtain repeat readings to reduce random errors, and state the calculated resolution or smallest division of each instrument. For example, a stopwatch may display 0.01 s, but human reaction time introduces a much larger uncertainty; your plan could use a light gate to circumvent this.
你的方法必须包含尽可能减小系统误差的具体步骤，例如检查螺旋测微器的零位误差，或在 0 °C 和 100 °C 标定温度计。说明你将如何通过重复读数来减小随机误差，并列出每台仪器的计算分辨率或最小分度值。例如，秒表可能显示 0.01 s，但人的反应时间会引入大得多的不确定度；你的计划可以使用光闸来避免这一问题。
When dealing with electrical circuits, describe precautions such as limiting current to avoid heating effects in resistors, or using a potential divider for smoother control. A preliminary trial is often helpful to determine suitable ranges for variables and to identify any unexpected safety hazards.
处理电路时，要描述预防措施，例如限制电流以避免电阻器的热效应，或使用分压器以更平滑地控制。进行一次预备试验通常有助于确定变量的适宜范围，并识别任何意外的安全隐患。
3. Making Accurate Measurements | 精确测量
Accuracy tells how close a reading is to the true value; precision describes the spread of repeated readings. In the exam, you must recognise the difference and suggest improvements for each. Use instruments with appropriate resolution: a micrometer screw gauge (0.01 mm) for wire diameters, vernier calipers (0.1 mm or 0.05 mm) for the length of a pendulum, and a digital multimeter (often 0.1% accuracy) for electrical quantities.
准确度表示读数与真值接近的程度；精密度描述重复读数的分散程度。在考试中，你必须识别二者的区别并针对每种情况提出改进建议。使用分辨率恰当的仪器：螺旋测微器（0.01 mm）测量导线直径，游标卡尺（0.1 mm 或 0.05 mm）测量摆长，数字万用表（通常精度 0.1%）测量电学量。
Avoid parallax error by viewing the scale perpendicularly; many ammeters and voltmeters have a mirror behind the scale to help. When reading a liquid meniscus, align your eye with the bottom of the meniscus. For a metre rule, use a set square or use the rule on its edge to eliminate parallax. Take several repeats and record all raw values, not just the mean. If a reading is clearly anomalous, you may exclude it, but must explain why.
通过垂直观察刻度来避免视差误差；许多安培表和伏特表在刻度后带有镜面以辅助对齐。读取液体弯月面时，视线应与弯月面底部齐平。使用米尺时，可借助直角尺或将尺竖立以消除视差。进行多次重复并记录所有原始数值，而不只是平均值。若某读数明显异常，可以剔除，但必须说明原因。
t of reaction time. Where possible, use electronic sensors: a light gate with a data logger records times to within 0.1 ms, enormously increasing precision.
计时是常见的薄弱环节。对于单摆，至少计时 20 次全振动（T = t/20）以减小反应时间的影响。可能的话，使用电子传感器：带数据记录器的光闸可以记录到 0.1 ms 的时间，极大地提高了精密度。
4. Recording and Presenting Data | 记录和呈现数据
All data must be tabulated neatly. The heading of each column should contain the symbol for the quantity, a slash, and the unit, e.g. 'l / mm' or 'T / s'. Record raw data to a number of significant figures that respects the instrument's resolution; do not artificially increase precision. Calculated quantities such as T², ln T, or 1/I should be placed in additional columns, with consistent decimal places or significant figures.
所有数据必须整齐地录入表格。每列表头应包含物理量符号、斜杠和单位，例如 “l / mm” 或 “T / s”。原始数据应按照仪器分辨率所能保证的有效数字位数记录；不可人为提高精密度。计算量如 T²、ln T 或 1/I 应放入附加列，并保持小数位数或有效数字一致。
Graphs are a central part of practical analysis. Use the largest possible scale to fill at least half of the graph paper. Label axes as 'quantity / unit' – for example, 'v / m s⁻¹' and 't / s'. Plot data points as small crosses or encircled dots; never simply use a dot. Draw a best-fit straight line or smooth curve through the points, paying attention to any anomalies that do not follow the trend.
图线是实践分析的核心部分。使用尽可能大的标度，至少占据坐标纸面积的一半。坐标轴标注为“量 / 单位”——例如 “v / m s⁻¹” 和 “t / s”。数据点用小十字或带圈的圆点标出；切勿只画一个点。穿过各点画出最佳拟合直线或光滑曲线，注意那些不遵循趋势的异常数据。
When you draw a best-fit line, ensure there is an even scattering of points above and below the line. For a curved plot, draw a smooth curve rather than joining points with a ruler. Never force a line through the origin unless there is a theoretical justification to do so.
绘制最佳拟合直线时，应使点均匀分布在线的上方和下方。对曲线图，应画出光滑曲线，而非用直尺逐点连接。除非有理论依据，否则切勿强行让直线通过原点。
5. Analysing Data and Using Graphs | 数据分析和图表运用
v² = u² + 2as can be written as v² = 2as if u = 0; plotting v² against s gives a gradient of 2a. In a simple pendulum, T = 2π√l/g (4π²/g)l, so a graph of T² against l yields a gradient of 4π²/g and an intercept of zero.
直线图是你最强大的工具。关系式 y = mx + c 常常编码了物理量。对自由落体，v² = u² + 2as 若 u = 0 可表示为 v² = 2as；作 v²–s 图得到斜率为 2a。在单摆实验中，T = 2π√l/g 可通过平方线性化：T² = (4π²/g)l，因此 T²–l 图给出斜率为 4π²/g，截距为零。
ly show the coordinates used. You may then calculate the required physical quantity, e.g. g = 4π² / gradient. Always include units throughout the calculation.
计算斜率时，选择最佳拟合直线上两个相距较远的点（非原始数据点）。画一个大三角形并计算 Δy/Δx。清楚标示所用坐标。随后计算所需的物理量，例如 g = 4π² / 斜率。整个过程始终要带单位。
To estimate the uncertainty in the gradient, draw the 'steepest' and 'shallowest' worst-fit lines that still pass through or near the error bars. The uncertainty in gradient m is given by (mmax − mmin olute uncertainty, e.g. g = (9.8 ± 0.2) m s⁻², demonstrates competent practical reporting.
要估计斜率的不确定度，画出能通过或接近误差棒的最陡和最平缓的最劣拟合线。斜率 m 的不确定度为 (mmax − mmin)/2。截距同理。将最终结果表示为带绝对不确定度的形式，例如 g = (9.8 ± 0.2) m s⁻²，可展示扎实的实践报告能力。
6. Evaluating Uncertainties and Errors | 不确定度和误差评估
esolution. For an analogue scale, it is ± half the smallest division. When several repeat readings are taken, the mean value's uncertainty can be estimated as half the range: Δx = (xmax − xmin)/2.
每个测量值都有其不确定度。对数字仪表单次读数，绝对不确定度通常取为 ± 分辨率。对模拟刻度，取 ± 最小分度值的一半。当取多次重复读数时，平均值的绝对不确定度可估计为半范围：Δx = (xmax − xmin)/2。
r Z = A − B, then ΔZ = ΔA + ΔB. For multiplication or division, percentage uncertainties add. If Z = A × B or Z = A / B, then %ΔZ = %ΔA + % power is involved, the percentage uncertainty is multiplied by the power: if Z = Aⁿ, then %ΔZ = n × %ΔA.
合成不确定度的规则取决于数学运算。加减时，绝对不确定度相加。若 Z = A + B 或 Z = A − B，则 ΔZ = ΔA + ΔB。乘除时，百分不确定度相加。若 Z = A × B 或 Z = A / B，则 %ΔZ = %ΔA + %ΔB。遇到乘方时，百分不确定度乘以指数：若 Z = Aⁿ，则 %ΔZ = n × %ΔA。
You must also distinguish between random and systematic errors. Random errors (e.g. fluctuation in a digital reading) cause scatter and can be reduced by averaging and better technique. Systematic errors (e.g. a faulty balance or incorrectly zeroed meter) shift all results in the same direction and are not reduced by repeats; they must be eliminated by calibration or correction. A consistent bias between your result and the accepted value often points to systematic error.
你还必须区分随机误差和系统误差。随机误差（例如数字读数的波动）引起数据分散，可通过取平均值和优化技术来减小。系统误差（例如天平故障或仪表零位不准）使所有结果朝同一方向偏移，不因重复而减小；必须通过校准或修正消除。你的结果与公认值之间存在一贯偏差，通常表明存在系统误差。
When writing a conclusion, compare the percentage difference between your value and the accepted value with the total experimental percentage uncertainty. If the difference falls within the uncertainty, the result is considered accurate within experimental error. If not, you must discuss unaccounted systematic errors.
撰写结论时，将你的数值与公认值之间的百分比差异与总实验百分不确定度进行比较。若差异落在不确定度范围内，则认为结果在实验误差范围内是准确的。否则必须讨论未加考虑的系统误差。
7. Drawing Conclusions and Discussing Limitations | 得出结论并讨论局限性
nal experimental value with its absolute uncertainty and provide a direct comparison, e.g. ' ich agrees with the accepted value of 1.10 × 10⁻⁶ Ω m within the experimental error of 4.4%.'
可靠的结论应说明实验证据是否支持最初假设。必须引用带有绝对不确定度的最终实验值，并给出直接比较，例如：“测得镍铬合金的电阻率为 (1.13 ± 0.05) × 10⁻⁶ Ω m，在 4.4% 的实验误差范围内与公认值 1.10 × 10⁻⁶ Ω m 一致。”
An evaluation must go beyond merely listing errors. For each significant source of uncertainty judged against the percentage uncertainty contribution, explain how it affected the data and propose a concrete improvement. For instance, 'The largest random error arose from timing by hand (∼10% uncertainty in the period); using a light gate linked to a data logger would reduce this to below 0.1%.' Quantified suggestions carry more weight.
评估工作不能仅仅罗列误差。应根据每个显著的不确定来源所占的百分不确定度贡献，解释它如何影响数据，并提出具体的改进措施。例如，“最大的随机误差来源于手工计时（周期的不确定度约 10%）；使用连接数据记录器的光闸可将此项降至 0.1% 以下。”量化的建议更有分量。
Identify any anomalous results that were omitted and explain why. If the experiment is precise but not accurate, discuss the likely systematic errors, such as a displaced zero or a theoretical simplification that was not valid under the experimental conditions.
指出任何因故省略的异常结果并说明理由。若实验精密但不准确，讨论可能的系统误差，例如零点偏移，或在实验条件下不适用的理论简化。
8. The Personal Investigation (Component 04) | 个人调查（组件04）
The Personal Investigation is your opportunity to demonstrate genuine scientific inquiry. You must select a topic within the physics syllabus, construct a testable hypothesis, design multiple experiments, and collect high-quality data. The emphasis is on independence, so
Published by TutorHao | Pre-U Physics Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图