Mastering Physics Practical Skills | 物理实验操作指南

📚 Mastering Physics Practical Skills | 物理实验操作指南

Physics is an experimental science, and a large part of your assessment in both IB and AQA specifications revolves around practical work. Whether you are designing an investigation, recording data, or analysing errors, a clear understanding of core practical skills is essential. This guide brings together the key techniques, terminology, and strategies you need to excel in the laboratory and in your written papers.

物理学是一门实验科学，在 IB 和 AQA 的考试中，很大一部分评估都与实验工作有关。无论你是在设计实验方案、记录数据还是分析误差，清晰地掌握核心实验技能都是至关重要的。本指南汇集了关键的技巧、术语和策略，帮助你在实验室和试卷中脱颖而出。

1. Safety First | 安全第一

Before any experiment, always assess the risks. Identify hazards such as hot surfaces, sharp objects, electrical circuits, or heavy masses. Wear appropriate personal protective equipment (PPE) – safety goggles, lab coats, and sometimes gloves. Know the location of the fire extinguisher, first-aid kit, and emergency stop buttons.

每次实验前，务必评估风险。识别热表面、尖锐物体、电路或重物等危险源。穿戴适当的个人防护装备——护目镜、实验服，有时还需要手套。熟悉灭火器、急救箱和紧急停止按钮的位置。

For electrical work, use low voltages (typically under 12 V DC unless instructed otherwise). Check leads for frayed insulation before connecting. Never leave a circuit unattended while powered. When heating substances, use tongs or heat-resistant mats, and point boiling tubes away from yourself and others.

在使用电器时，采用低电压（除非另有说明，通常低于 12 V 直流电）。连接前检查导线绝缘层是否磨损。电路通电时切勿无人看管。加热物质时，使用钳子或耐火垫，并将沸腾管口朝向远离自己和他人的方向。

2. Selecting and Using Equipment | 选择和使用仪器

Choose the right instrument for the measurement you need. For length, a metre rule gives 1 mm resolution, vernier calipers give 0.1 mm or 0.02 mm, and a micrometer screw gauge gives 0.01 mm. For time, a digital stopwatch may read to 0.01 s, but human reaction time is around 0.2 s – this is the practical limit.

根据测量需要选择合适的仪器。测量长度时，米尺的分辨率为 1 mm，游标卡尺可达到 0.1 mm 或 0.02 mm，螺旋测微计的分辨率为 0.01 mm。测量时间时，数字秒表读数可达 0.01 s，但人的反应时间约为 0.2 s——这是实际的限制。

When using analogue instruments, always record to half the smallest scale division. For digital instruments, record every digit shown – including trailing zeros, as they indicate precision. Always zero the instrument (e.g., a balance, a voltmeter) before starting, and take repeat readings to improve reliability.

使用模拟仪表时，始终记录到最小刻度的一半。对于数字仪表，记录显示的所有数字——包括末尾的零，因为它们表示精度。开始测量前务必调零（例如天平、电压表），并进行重复读数以提高可靠性。

3. Measurement Techniques and Reading Instruments | 测量技巧与仪器读数

To minimise parallax error, your eye must be directly in line with the pointer and scale. On a mirror-backed scale, align the pointer with its own reflection. Use a set square when measuring the height of a pendulum bob or a ruler on a bench. For thermometers, stir the liquid and wait for thermal equilibrium before reading.

为了减少视差，眼睛必须与指针及刻度在一条直线上。在带有镜面背板的刻度盘上，让指针与其镜像重合。测量摆锤高度或桌面上直尺的高度时，使用三角尺辅助。温度计读数前应搅拌液体并等待热平衡。

When measuring oscillating quantities, such as the period of a pendulum, measure the time for multiple oscillations (e.g., 10 or 20) and then divide to find the period. This reduces the impact of reaction-time error by the factor of the number of oscillations counted.

测量振荡量时，例如单摆的周期，应测量多次振荡（例如 10 或 20 次）的总时间，再除以次数得到周期。这样可以将反应时间误差的影响减小到重复次数的分之一。

4. Understanding Uncertainty | 理解不确定度

Every measurement has an uncertainty. The absolute uncertainty of a single reading is often taken as ± half the smallest division (for analogue) or ± the last digit (for digital, unless stated otherwise). For a measured quantity obtained by difference, the absolute uncertainty is roughly twice the instrument uncertainty.

每次测量都有不确定度。单次读数的绝对不确定度通常取 ± 最小分度的一半（模拟仪表）或 ± 最后一位数字（数字仪表，除非另有说明）。对于通过差值得到的量，其绝对不确定度大约是仪器不确定度的两倍。

Percentage uncertainty is calculated by (absolute uncertainty / measured value) × 100%. This is especially useful when comparing the quality of measurements of different magnitudes. For multiple measurements, the spread (range/2) can be used as an estimate of the absolute uncertainty.

百分不确定度由（绝对不确定度 / 测量值）× 100% 计算得出。在比较不同量级测量的质量时，百分比不确定度尤其有用。对于多次测量，可用极差的一半（范围/2）作为绝对不确定度的估计值。

5. Types of Errors (Systematic vs. Random) | 误差类型（系统误差与随机误差）

Random errors cause readings to be scattered about the true value and can be reduced by taking many repeats and calculating a mean. They arise from unpredictable variations in the environment or observer judgement. Systematic errors, on the other hand, shift all readings in one direction and do not average out.

随机误差导致读数在真值附近分散分布，可以通过多次重复测量并取平均值来减小。它们源于环境或观察者判断的不可预测变化。而系统误差会使所有读数向同一个方向偏移，无法通过取平均值来消除。

Common systematic errors include an instrument that is not zeroed, a scale that is incorrectly calibrated, or taking a measurement with a constant parallax offset. The key is to recognise the type of error: random errors affect precision, while systematic errors affect accuracy.

常见的系统误差包括仪器未调零、标尺校准错误，或者测量时存在固定的视差偏移。关键是要认清误差类型：随机误差影响精密度，系统误差影响准确度。

6. Data Recording and Presentation | 数据记录与呈现

Design a clear results table before starting. Each column must have a heading that includes the quantity and its unit, separated by a forward slash (e.g., Voltage / V). All raw readings should be recorded here, along with processed quantities like averages. Use the same number of decimal places consistently for each column.

开始实验前设计清晰的记录表格。每一列必须有标题，包括物理量及其单位，用斜杠分隔（例如 Voltage / V）。所有原始读数应记录在此，同时记录平均值等处理后的量。同一列的数据应保持小数位数一致。

When presenting data, distinguish between independent variable (x-axis), dependent variable (y-axis), and controlled variables. Only tabulate values that you actually measure or calculate; do not fill cells with insignificant zeros unless they are meaningful to the precision.

呈现数据时，区分自变量（x 轴）、因变量（y 轴）和控制变量。只记录你实际测量或计算的值；不要用无意义的零填充单元格，除非它们反映了精度。

7. Graphing Skills | 绘图技巧

Plot graphs on proper graph paper or using software. Choose scales that make the plotted points occupy more than half the grid in each direction. Label axes with quantities and units, and use linear scales unless a logarithmic relationship is expected. Plot data points with small crosses (×) or circled dots, and add error bars if uncertainties are known.

在合适的坐标纸或软件上作图。所选坐标轴标度应使数据点占据各方向一半以上的网格区域。标注坐标轴及单位，除非预期是对数关系，否则采用线性标度。用小的十字叉（×）或带圈圆点标绘数据点，如果已知不确定度，还应添加误差棒。

Draw a line of best fit – not a dot-to-dot connection. The line should be smooth and pass as close as possible to the points, with an equal number of points on each side. If the relationship is known to be linear, use a transparent ruler. For curves, draw a smooth trend by hand or with a flexicurve.

绘制最佳拟合线——不要逐点连线。线条应平滑，尽可能靠近所有点，两侧点数大致相等。如果已知关系是线性的，使用透明直尺辅助。如果是曲线，用手绘或曲线尺画出平滑的趋势线。

8. Linearization and Analysis | 线性化与分析

Many practicals aim to verify a physical relationship of the form y = mx + c. If raw data yields a curve, transform one axis to straighten it. For example, if you suspect y ∝ x², plot y against x²; if y ∝ 1/x, plot y against 1/x. The gradient and intercept of this linear graph then give meaningful physical constants.

许多实验旨在验证 y = mx + c 形式的物理关系。如果原始数据图呈曲线，可以通过变换其中一个轴来拉直。例如，若你猜测 y ∝ x²，就绘制 y–x² 图；若 y ∝ 1/x，就绘制 y–1/x 图。此线性图的斜率和截距便给出有意义的物理常数。

To find the gradient, use a large triangle on the best-fit line – do not use table points. Gradient = Δy / Δx. The y-intercept is read directly where x = 0. Always state the units of gradient and intercept. Where possible, compare your experimental constant with the accepted literature value by calculating a percentage difference.

求斜率时，在最佳拟合线上取一个大三角形——不要使用表格中的点。斜率 = Δy / Δx。纵截距从 x = 0 处直接读取。始终标明斜率和截距的单位。尽可能将你的实验常数与公认文献值进行比较，计算百分比差异。

9. Error Propagation | 误差传递

When you combine measurements to calculate a final result, the uncertainties propagate. Simple rules apply: for addition or subtraction (Z = A ± B), add absolute uncertainties (ΔZ = ΔA + ΔB). For multiplication or division (Z = A × B or A/B), add percentage uncertainties (%Z = %A + %B).

当你组合测量值来计算最终结果时，不确定度会传递。简单的规则是：对于加法或减法（Z = A ± B），将绝对不确定度相加（ΔZ = ΔA + ΔB）。对于乘法或除法（Z = A × B 或 A/B），将百分不确定度相加（%Z = %A + %B）。

When a quantity is raised to a power (Z = Aⁿ), multiply the percentage uncertainty by |n|. For logarithms and trigonometric functions, more advanced methods are used, but at this level, you will often simply be asked to estimate the worst-case maximum and minimum possible results.

当物理量做幂运算时（Z = Aⁿ），将百分不确定度乘以 |n|。对于对数和三角函数，需使用更高级的方法，但在目前阶段，通常会要求你估算最坏情况下可能的最大值和最小值。

10. Evaluating the Experiment | 评估实验

An evaluation must identify the main sources of uncertainty and suggest realistic improvements. Comment on the size of your percentage uncertainties: generally, if the total percentage uncertainty is larger than the percentage difference from the accepted value, your result is consistent with the accepted value within experimental error.

评估环节必须指出不确定度的主要来源，并提出切实可行的改进建议。评论百分不确定度的大小：通常，如果总百分不确定度大于与公认值的百分比差，说明在实验误差范围内你的结果与公认值一致。

Do not simply list human error or “readings were not taken accurately.” Be specific: for example, “the digital balance drifted, causing readings to increase over time,” or “the laser beam spot was large, making it difficult to judge the exact centre on the screen.” Then propose a concrete fix: “use a balance with a draft shield” or “use a narrower aperture to reduce spot size.”

不要只是列举人为错误或“读数不准确”。要具体：例如，“数字天平发生漂移，导致读数随时间增大”，或者“激光光斑较大，难以在屏幕上判断精确中心”。然后提出具体的改进措施：“使用带防风罩的天平”或“使用更小的光阑以减小光斑”。

11. Common Practicals and Their Pitfalls | 常见实验及易错点

In pendulum investigations (determining g), avoid large amplitudes (keep < 10°) to maintain simple harmonic motion. Measure the effective length from the point of suspension to the centre of mass of the bob. In a free-fall experiment using a trapdoor and an electromagnet, ensure the ball is released cleanly and the timing circuit has minimal lag.

在单摆实验中（测定 g），避免大的振幅（保持 < 10°）以维持简谐运动。有效摆长应从悬挂点到摆锤的质心。在使用电磁铁和光隙门的自由落体实验中，确保小球被干净利落地释放，且计时电路延时极小。

For ohm’s law and resistivity practicals, the current must not be too high to avoid heating the wire, which changes its resistance. Use a rheostat to vary current and take readings quickly. For a diffraction grating experiment, ensure the laser beam is perpendicular to the screen, and measure distances with a metre rule and a vernier scale for the fringe spacing.

在做欧姆定律和电阻率实验时，电流不应过大，以免加热导线从而改变电阻。使用变阻器改变电流并快速读数。在衍射光栅实验中，应确保激光束垂直于屏幕，并用米尺和游标卡尺配合测量条纹间距。

12. Achieving Top Marks in Practical Assessments | 在实验评估中获得高分

In IB, your Internal Assessment (IA) rewards personal engagement, exploration, and thorough analysis. State a clear, focused research question. Demonstrate initiative in modifying the procedure and reflecting on the method. In AQA, the practical endorsement and written questions on required practicals assess your ability to follow procedures, handle data, and evaluate results. Use precise scientific language throughout.

在 IB 中，内部评估（IA）看重个人投入、探索和透彻分析。提出一个明确、聚焦的研究问题。在修改程序和反思方法上展现主动性。在 AQA 中，实验操作签核及相关必做实验的笔试题目，评估你遵循程序、处理数据和评估结果的能力。全程使用精确的科学语言。

Always connect your discussion back to the underyling physics. For example, do not just say “the line is straight”; explain that a straight line through the origin shows direct proportionality, confirming the relationship predicted by the theory. When stating a final value, give it as result ± absolute uncertainty, with the correct unit and to the appropriate significant figures.

始终将讨论与背后的物理原理联系起来。例如，不要只说“线是直的”；要解释一条过原点的直线表明正比关系，验证了理论预测的关系。在给出最终数值时，以结果 ± 绝对不确定度的形式呈现，带正确单位，并取适当的有效数字。

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Mastering Physics Practical Skills | 物理实验操作指南