IB & CIE Physics: Experimental Skills and Practical Guide | IB CIE 物理：实验操作指南

📚 IB & CIE Physics: Experimental Skills and Practical Guide | IB CIE 物理：实验操作指南

Physics is an experimental science, and a strong grasp of practical skills is essential for success in both IB and CIE A-Level Physics. Whether you are preparing for the IB internal assessment (IA) or the CIE Paper 3 practical exam, this guide covers key techniques, error analysis, data presentation, and safe laboratory practice. Mastering these skills not only helps you score highly in assessments but also trains you to think like a scientist.

物理是一门实验科学，扎实的实验技能对于在IB和CIE A-Level物理中取得成功至关重要。无论你在准备IB内部评估（IA）还是CIE Paper 3实验考试，本指南将涵盖关键的实验技术、误差分析、数据展示以及安全的实验室操作。掌握这些技能不仅能帮助你在考核中获得高分，也能训练你像科学家一样思考。

1. Introduction to Practical Work | 实验概述

Practical work in physics develops scientific thinking, manipulative skills, and the ability to interpret data critically. Both IB and CIE syllabi emphasize planning, implementation, analysis, and evaluation as four essential stages of any investigation. In the IB IA, you design and carry out your own experiment; in CIE Paper 3, you follow given instructions while demonstrating correct use of apparatus and recording data with appropriate precision.

物理实验旨在培养科学思维、操作技能和批判性解读数据的能力。IB和CIE教学大纲都强调计划、实施、分析和评估是任何探究的四个关键阶段。在IB内部评估中，你需要自行设计并完成实验；在CIE Paper 3中，你按照给定指导操作，同时展示正确使用仪器并以适当精度记录数据的能力。

Marks are awarded for systematic presentation, correct manipulation, accurate measurements, and insightful evaluation of uncertainties and limitations. Always read the assessment criteria before you begin.

评分依据包括系统性的呈现、规范的操作、精确的测量以及对不确定度和局限性的深入评估。开始实验前，务必先阅读评分标准。

2. Measuring Instruments and Their Uses | 测量仪器及其使用

Choosing the right instrument for a measurement determines the precision you can achieve. The table below summarizes common instruments in a school laboratory.

选择合适的测量仪器决定了你能达到的精度。下表总结了学校实验室中的常用仪器。

Instrument	Typical Range	Precision / Least Count	Common Use
Metre rule	0 – 100 cm	1 mm	Length of a pendulum, height
Vernier calipers	0 – 15 cm	0.1 mm or 0.05 mm	Diameter of a cylinder, thickness
Micrometer screw gauge	0 – 25 mm (or larger)	0.01 mm	Wire diameter, thin sheet thickness
Stopwatch	0 – 9 h	0.01 s (digital)	Time of fall, period of oscillation
Thermometer (liquid-in-glass)	-10 °C – 110 °C	0.5 °C or 1 °C	Temperature change of water
Ammeter (analogue)	0 – 1 A / 0 – 5 A	0.02 A (typical)	Current in a circuit
Voltmeter (digital)	0 – 20 V	0.01 V	Potential difference across a component

Always check the least count before you start. For analogue scales, estimate to half of the smallest division; for digital instruments, the reading is taken as shown, but the uncertainty is often ± the last digit or as stated in the manual.

开始测量前务必检查最小刻度。对于模拟刻度，估读到最小分度的一半；对于数字仪器，直接读数，但不确定度通常为±末位数字或按照说明书规定。

3. Reading Scales and Precision | 读数与精度

Parallax error occurs when your eye is not perpendicular to the scale. To avoid it, keep your line of sight directly above the pointer or liquid meniscus. For mercury or water thermometers, read the bottom of the meniscus at eye level.

当视线未与刻度垂直时会产生视差。为避免视差，眼睛应位于指针或液面正上方。对于水银或水温度计，应在与液面弯月面底部齐平的位置读数。

Record all raw data with a consistent number of decimal places that reflects the instrument’s precision. For example, if using a metre rule with 1 mm divisions, write 15.3 cm, not 15 cm or 15.30 cm. With vernier calipers reading 3.45 cm, you may write 3.45 cm, implying a precision of 0.01 cm.

记录所有原始数据时，应使用一致的小数位数以反映仪器精度。例如，使用最小刻度为1 mm的米尺时，应记为15.3 cm，而非15 cm或15.30 cm。若游标卡尺读数为3.45 cm，记为3.45 cm即可，表明精度为0.01 cm。

Taking repeated readings and calculating the mean reduces the effect of random errors. Always take at least three readings for critical measurements and check for outliers.

多次测量并取平均值可减小随机误差的影响。关键测量至少进行三次，并检查有无异常值。

4. Uncertainties and Errors | 不确定度与误差

Errors are not the same as mistakes. Systematic errors cause readings to deviate from the true value by a consistent amount (e.g., zero error on a micrometer). Random errors cause readings to scatter around the true value due to unpredictable variations.

误差不同于错误。系统误差导致读数以固定量偏离真值（例如千分尺的零误差）。随机误差则由于不可预测的变动使得读数围绕真值散布。

Uncertainty quantifies the range within which the true value is expected to lie. The absolute uncertainty of a single measurement is usually taken as half the smallest scale division (for analogue) or the least count (for digital). When multiple readings are taken, the uncertainty can be estimated as half the range (max – min)/2 or the standard deviation.

不确定度量化了真值预期所在的范围。单次测量的绝对不确定度通常取最小分度的一半（模拟仪器）或末位数字（数字仪器）。多次测量时，不确定度可估计为极差的一半（最大值–最小值）/2或标准偏差。

For calculations, uncertainties propagate according to simple rules. When adding or subtracting quantities, absolute uncertainties add: If R = A + B, then ΔR = ΔA + ΔB. When multiplying or dividing, relative (percentage) uncertainties add.

计算时，不确定度遵循简单传播规则。加减运算中绝对不确定度相加：若R = A + B，则ΔR = ΔA + ΔB。乘除运算中相对（百分比）不确定度相加。

If R = A × B or R = A ÷ B, then ΔR/R = ΔA/A + ΔB/B

Always express the final result as (best estimate ± absolute uncertainty) with the correct unit. Quote the uncertainty to one significant figure (or two if the leading digit is 1) and round the best estimate to the same decimal place.

最终结果应表示为（最佳估值 ± 绝对不确定度）并带正确单位。不确定度保留一位有效数字（首位是1时可保留两位），最佳估值则四舍五入至相同小数位。

5. Recording and Presenting Data | 记录与呈现数据

Data tables must be neat and self-explanatory. Each column should have a heading that includes the quantity and its unit separated by a slash, e.g., ‘Length L / cm’. Raw data and calculated quantities belong in separate columns. Use consistent significant figures throughout.

数据表必须整洁且自明。每列应有表头，包含物理量及其单位，用斜线分隔，例如“长度 L / cm”。原始数据与计算量应分列放置。全表采用一致的显著数字。

Never erase raw data; if you make a mistake, cross it out with a single line and write the correction nearby. Examiners look for evidence that you recorded data directly, not after editing.

切勿擦除原始数据；若写错，用单线划掉并在旁边写上修正值。考官寻找的是你直接记录数据的证据，而非事后编辑的痕迹。

When processing data, show one sample calculation in full, then tabulate the results. State any formulae used and explain your steps clearly.

处理数据时，完整展示一次样本计算，然后将结果制成表格。说明使用的公式，并清晰解释计算步骤。

6. Graphing Techniques | 绘图技巧

Plot the independent variable on the x-axis and the dependent variable on the y-axis. Use a sharp pencil and draw data points as small crosses or circled dots. Choose a scale that makes the plotted points occupy at least half the graph area in both directions. Label each axis with the quantity and unit, e.g., ‘Time t / s’.

将自变量标在x轴，因变量标在y轴。用削尖的铅笔将数据点画成小十字或加圈圆点。选取比例时要使点占据图表区域至少一半。每个坐标轴标上物理量和单位，例如“时间 t / s”。

Draw a best-fit straight line or smooth curve that passes as close as possible to all points, with roughly equal numbers of points on either side. Do not force the line through the origin unless the theoretical relationship demands it. If uncertainties are known, add error bars to each point before fitting.

画出最贴近所有点的最佳拟合直线或光滑曲线，使点大致均匀分布在线的两侧。除非理论关系要求，否则不要强制通过原点。若已知不确定度，在拟合前先给每个点加上误差棒。

Calculate the gradient and intercept from the best-fit line, not from raw data points. For a straight line, choose two points far apart on the line, not necessarily data points, label their coordinates, and use gradient = (y₂ – y₁)/(x₂ – x₁). Always include units for gradient and intercept.

应使用最佳拟合线而非原始数据点来计算斜率和截距。对于直线，选取线上相距较远的两点（不必是数据点），标注其坐标，使用斜率 = (y₂ – y₁)/(x₂ – x₁)。斜率与截距务必带单位。

7. Linearization and Analysis | 线性化与分析

Many physics relationships are non-linear, but you can transform them into linear form to extract constants. For example, the period of a simple pendulum T = 2π√(L/g) squares to T² = (4π²/g)L. Plotting T² against L gives a straight line through the origin, and g can be found from the gradient: g = 4π² / gradient.

许多物理关系是非线性的，但可以通过变换转化为直线形式来求得常数。例如，单摆周期 T = 2π√(L/g) 可平方为 T² = (4π²/g)L。绘制 T²–L 图可得过原点直线，由斜率可求 g：g = 4π² / 斜率。

Similarly, for exponential decay A = A₀ e^(-λt), take natural logs: ln A = ln A₀ – λ t. A graph of ln A versus t yields a straight line whose gradient is -λ.

同样，对于指数衰减 A = A₀ e^(-λt)，取自然对数得 ln A = ln A₀ – λ t。以 ln A 对 t 作图得到直线，其斜率为 -λ。

Always state the relationship you expect, explain what you plot on each axis, and show how the unknown quantity relates to the gradient or intercept. This demonstrates deep understanding and is rewarded in both IB and CIE marking schemes.

务必说明预期的关系，解释各轴所绘内容，并展示未知量与斜率或截距的关系。这体现了深入理解，在IB和CIE评分方案中均可获得加分。

8. Planning an Investigation | 设计探究

A good plan states a clear, focused research question and identifies the independent, dependent, and controlled variables. For IB IA, you must justify the number of repeats, the range of values chosen, and the apparatus selected.

一份好的计划应提出清晰、聚焦的研究问题，并确定自变量、因变量和控制变量。在IB内部评估中，必须论证重复次数、所选数值范围以及仪器选择。

Describe how you will control each variable and minimize sources of systematic and random error. Draw a labeled diagram of the experimental set-up. Specify a preliminary trial or pilot study to check the procedure.

描述如何控制每个变量，以及如何最小化系统误差和随机误差的来源。画出带标注的实验装置图。安排一次预实验或先导研究以检查流程。

Risk assessment is also part of planning: identify potential hazards (e.g., hot surfaces, falling masses, electrical shock) and state the precautions you will take.

风险评估也是计划的一部分：识别潜在危险（例如高温表面、重物坠落、触电），并说明将采取的预防措施。

9. Safety in the Laboratory | 实验室安全

Always wear safety goggles when heating substances, using springs under tension, or working with projectiles. Tie back long hair and secure loose clothing. Know the location of the fire extinguisher, first-aid kit, and emergency exits.

加热物质、使用处于拉力下的弹簧或处理抛射体时，务必佩戴护目镜。长发扎起，宽松衣物固定好。清楚灭火器、急救箱和紧急出口的位置。

Handle electrical circuits with care: never connect a voltmeter in series, and always switch off the power before making changes. Avoid touching bare wires and keep water away from electrical equipment.

小心操作电路：切勿将电压表串联，改动电路前务必关断电源。避免触摸裸线，并保持水电隔离。

When using mercury thermometers, handle them gently to avoid breakage. Report any spillage or breakage immediately. Dispose of waste according to your school’s guidelines.

使用水银温度计时，轻拿轻放以防破裂。任何泄漏或破碎应立即报告。按学校规定处理废弃物。

10. Common IB & CIE Experiments | 常见IB与CIE实验

Below are some frequently assessed experiments. For each, pay special attention to the main sources of uncertainty and the data analysis required.

以下是几个常考实验。每个实验都需要特别注意主要的不确定度来源和所需的数据分析。

Determining g by free fall: Drop a ball-bearing from a known height and measure time of fall. Use s = ½gt². Plot s vs t²; gradient = ½g. Main uncertainty: reaction time on stopwatch; reduce by using electronic timing or large distances.
测定重力加速度g（自由落体）：从已知高度释放小球，测量下落时间。使用 s = ½gt²。绘制 s–t² 图，斜率 = ½g。主要不确定度：秒表反应时间；可使用电子计时或增大下落距离来减小。
Oscillation of a spring: Measure period T for different masses m. T = 2π√(m/k). Plot T² vs m; gradient = 4π²/k. Ensure spring oscillates vertically without swinging.
弹簧振动：测量不同质量 m 对应的周期 T。T = 2π√(m/k)。绘制 T²–m 图，斜率 = 4π²/k。确保弹簧竖直振动而不摇摆。
Ohm’s law and resistivity: Vary the voltage across a fixed resistor or a wire, measure current I and potential difference V. R = V/I. For resistivity, plot V vs I; gradient gives R, then ρ = RA/L. Control temperature to keep resistance constant.
欧姆定律与电阻率：改变定值电阻或导线两端的电压，测量电流I和电势差V。R = V/I。对于电阻率，绘制 V–I 图，斜率得 R，然后 ρ = RA/L。控制温度以保持电阻恒定。
Young’s modulus: Stretch a long, thin wire with known loads. Measure extension with a travelling microscope or vernier scale. Plot stress (F/A) vs strain (e/L₀); gradient = E. Avoid exceeding the elastic limit.
杨氏模量：用已知负载拉伸一根长细导线，通过游标显微镜或游标尺测量伸长量。绘制应力 (F/A)–应变 (e/L₀) 图，斜率 = E。避免超过弹性极限。
Diffraction grating: Use a laser and grating to measure angles of bright orders. d sinθ = nλ. Measure θ on both sides of the central maximum to reduce zero error.
衍射光栅：使用激光和光栅测量亮纹级次的衍射角。d sinθ = nλ。在中央明纹两侧测量θ以减小零位误差。

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IB & CIE Physics: Experimental Skills and Practical Guide | IB CIE 物理：实验操作指南