IGCSE Physics: A Guide to Experimental Skills | IGCSE 物理：实验操作指南

📚 IGCSE Physics: A Guide to Experimental Skills | IGCSE 物理：实验操作指南

Practical skills are at the heart of IGCSE Physics. Whether you are measuring the extension of a spring or investigating the refraction of light, a solid grasp of experimental techniques is essential for both your coursework and the practical-based exam papers. This guide will walk you through the key concepts, from choosing the right instrument to evaluating the reliability of your data. By mastering these skills, you will not only achieve higher marks but also develop a deeper understanding of how physics works in the real world.

实验技能是 IGCSE 物理的核心。无论你是测量弹簧的伸长量还是研究光的折射，扎实掌握实验技术对于课程作业和基于实验的考试都至关重要。本指南将带你梳理关键概念，从选择合适的仪器到评估数据的可靠性。掌握这些技能不仅能帮你获得更高分数，更能让你深入理解物理在真实世界中的运作方式。

1. Safety in the Lab | 实验室安全

Before starting any experiment, always assess potential hazards. For example, when heating water, use a heatproof mat and never leave the apparatus unattended. Electrical circuits should be checked by your teacher before switching on the power supply.

开始任何实验之前，务必评估潜在风险。例如，加热水时要使用隔热垫，并且绝不能无人看管。电路在接通电源前应先由老师检查。

Wear safety goggles when working with springs under tension, hot liquids, or bright light sources like lasers or discharge tubes. Tie back long hair and remove dangling jewellery to avoid accidents.

在操作处于拉伸状态的弹簧、热液体或激光、放电管等强光源时，应佩戴护目镜。长发需束起，取下悬挂的饰品以避免意外。

Always follow the specific risk assessment provided in your practical exam or worksheet. If a chemical is used, note any hazard symbols and know the correct disposal method.

务必遵循实验考试或实验单中给出的具体风险评估。如果使用化学品，要注意危险符号并了解正确的处置方法。

2. Choosing the Right Measuring Instrument | 选择合适的测量仪器

Selecting an instrument with an appropriate resolution and range is fundamental. For length, a metre rule can measure to the nearest millimetre (0.1 cm), while vernier calipers can read to 0.1 mm, and a micrometer screw gauge can achieve 0.01 mm precision.

选择具有合适分辨率和量程的仪器是基本要求。测量长度时，米尺可精确到毫米（0.1 cm），游标卡尺可读至 0.1 mm，而螺旋测微器可达到 0.01 mm 的精度。

For time, digital stopwatches typically display 0.01 s, but human reaction time is around 0.2 s, so repeated measurements and averaging are more important than the instrument’s display resolution.

对于时间，数字秒表通常显示 0.01 s，但人的反应时间约为 0.2 s，因此重复测量取平均值比仪器的显示分辨率更重要。

When measuring current or voltage, ensure the ammeter is connected in series and the voltmeter in parallel. Choose a scale that gives a reading near the upper end to keep the percentage uncertainty low.

测量电流或电压时，确保电流表串联、电压表并联。选择能使读数接近满偏的挡位，以降低百分百不确定度。

3. Measurements and SI Units | 测量与 SI 单位

All measurements in physics are based on the International System of Units (SI). The base quantities and their units you must know include: length (metre, m), mass (kilogram, kg), time (second, s), electric current (ampere, A), and temperature (kelvin, K).

物理学中的所有测量都基于国际单位制（SI）。你必须掌握的基本物理量及其单位包括：长度（米，m）、质量（千克，kg）、时间（秒，s）、电流（安培，A）和温度（开尔文，K）。

Derived units, such as the newton (N = kg m s⁻²) and the joule (J = N m), should be expressed in terms of base units where required. Always write the correct unit alongside a numerical value in a table and on a graph axis.

导出单位，如牛顿（N = kg m s⁻²）和焦耳（J = N m），在需要时应表示为基本单位的形式。在表格和图表坐标轴中，务必在数值旁写出正确的单位。

Use prefixes like milli (m, 10⁻³), centi (c, 10⁻²), kilo (k, 10³), and mega (M, 10⁶) appropriately. Converting centimetres to metres before substituting into a formula prevents decimal errors.

合理使用词头，如毫（m，10⁻³）、厘（c，10⁻²）、千（k，10³）和兆（M，10⁶）。在代入公式前将厘米转换为米可以避免小数点错误。

4. Errors and Uncertainties | 误差与不确定度

An error is the difference between a measured value and the true value. Systematic errors arise from the apparatus (e.g., a zero error on a micrometer) or the method, and they cause all readings to be shifted by a constant amount. These can be reduced by calibration or by subtracting the zero reading.

误差是测量值与真实值之间的差异。系统误差源于仪器（如螺旋测微器的零误差）或方法，它会使所有读数都偏移一个固定的量。可通过校准或减去零读数来减小此类误差。

Random errors occur due to unpredictable fluctuations, such as changes in reaction time or environmental conditions. Repeating measurements and calculating the mean reduces their effect. The spread of readings (range ÷ 2) can estimate the random uncertainty.

随机误差由不可预测的波动引起，例如反应时间的变化或环境条件的改变。重复测量并计算平均值可以减小其影响。读数的散布范围（极差÷2）可用于估算随机不确定度。

Precision refers to how close repeated measurements are to each other, while accuracy refers to how close a result is to the accepted true value. A set of readings can be precise but inaccurate due to a systematic error.

精密度指重复测量值之间的接近程度，而准确度指结果与公认真实值之间的接近程度。一组数据可能因系统误差而精密但不准确。

5. Recording Data in Tables | 用表格记录数据

Design your results table before starting the experiment. Each column should have a heading that includes the quantity name and its unit separated by a slash, such as ‘Length / cm’ or ‘Current / A’. The independent variable is usually placed in the first column.

在开始实验之前设计好结果表格。每一列都应有包含物理量名称和单位的表头，用斜线分隔，例如’Length / cm’或’Current / A’。自变量通常放在第一列。

Record readings to the same number of decimal places, consistent with the instrument’s resolution. For example, if using a metre rule marked in mm, write 12.3 cm, not 12.30 cm. Raw data should not be ‘adjusted’.

按照仪器分辨率保持统一的小数位数记录读数。例如，若使用毫米刻度的米尺，应记为 12.3 cm，而非 12.30 cm。原始数据不应被“修饰”。

Include columns for processed data, such as the mean of repeat readings, and calculated quantities like resistance (R = V / I). Show sample calculations clearly beside the table or in a dedicated section.

还要包含处理数据的列，如重复读数的平均值，以及计算出的物理量，如电阻（R = V / I）。在表格旁或专门区域清晰展示样本计算过程。

6. Plotting and Analysing Graphs | 绘制与分析图表

Plot a graph with the independent variable on the x-axis and the dependent variable on the y-axis. Choose scales that allow your data points to occupy more than half the graph grid in both directions. Label axes with quantity and unit, e.g., ‘Extension / cm’.

绘制图表时，将自变量放在 x 轴，因变量放在 y 轴。选择比例尺使数据点在两个方向上都能占据超过一半的图纸网格。用物理量和单位标注坐标轴，如’Extension / cm’。

Plot points with small, neat crosses or dots inside circles. Do not join them dot-to-dot with a ruler; instead, draw the best-fit straight line or smooth curve that captures the trend. A line of best fit should have a roughly equal number of points on either side of it.

用小的整齐叉号或带圈圆点标出数据点。不要用尺子逐点连线；而应画出反映趋势的最佳拟合直线或光滑曲线。最佳拟合线两侧的数据点数目应大致相等。

To find the gradient of a straight-line graph, select two points far apart on the line and use:

gradient = (y₂ – y₁) / (x₂ – x₁)

计算直线图的梯度时，在线段上选取相距较远的两点，并使用：

梯度 = (y₂ – y₁) / (x₂ – x₁)

The y-intercept can be read directly from the graph where x = 0. Always state the unit of the gradient and intercept. When the relationship is proportional, the straight line passes through the origin.

y 轴截距可直接在 x = 0 处从图上读出。始终注明梯度和截距的单位。当关系为正比关系时，直线通过坐标原点。

7. Key Experimental Techniques | 关键实验技术

For pendulum timing, measure the time for 10 or 20 complete oscillations and then divide to find the period. Starting and stopping the stopwatch at the centre of the swing reduces reaction-triggered error further.

测量单摆周期时，记录 10 或 20 次完整摆动的时间然后求平均值得到周期。在摆动的中心点开始和停止秒表可进一步减少由反应时间引起的误差。

When using ray boxes and lenses, draw all rays with a sharp pencil and ruler. Mark the incident ray, refracted ray, and normal clearly. Measure angles with a protractor, ensuring the baseline aligns with the normal.

使用光线盒和透镜时，用削尖的铅笔和直尺画出所有光线。清晰标出入射光线、折射光线和法线。用量角器测量角度，确保底线与法线对齐。

For circuit investigations, always switch off between readings to prevent heating effects that change resistance. A variable resistor (rheostat) is useful for controlling current and taking multiple readings. Check connections for tightness.

在电路探究中，每次读数后都要断开开关，以防热效应导致电阻变化。滑动变阻器（变阻器）可用于控制电流并获得多组数据。检查连接是否牢固。

8. Worked Examples of Common Experiments | 常见实验示例

Measuring the density of an irregular solid: Measure mass using a balance. Submerge the solid in a measuring cylinder with water and record the volume rise. The volume of the solid equals the difference between the final and initial water levels. Then apply:

density = mass / volume

测量不规则固体的密度：用天平测量质量。将固体浸入盛有水的量筒中，记录水位的升高。固体的体积等于最终与初始水位之差。然后运用：

密度 = 质量 / 体积

Investigating Hooke’s Law: Suspend a spring from a clamp, add masses, and measure the extension each time. Plot a graph of force (F = mg) against extension. The gradient gives the spring constant, k. The straight line shows F ∝ x up to the limit of proportionality.

探究胡克定律：将弹簧悬挂在铁架上，增加砝码并每次测量伸长量。绘制力（F = mg）与伸长量的关系图。梯度给出弹簧常数 k。直线表明在比例极限内 F ∝ x。

Finding the resistance of a wire: Set up a circuit with an ammeter, voltmeter, and the wire. Vary the current and record corresponding voltage readings. Plot a V-I graph; the gradient equals the resistance. To minimise heating, use low currents and take quick readings.

求导线的电阻：搭建包含电流表、电压表和导线的电路。改变电流并记录对应的电压读数。绘制 V-I 图，其梯度等于电阻。为减小发热影响，应使用小电流并快速读数。

9. Evaluating the Experiment and Suggesting Improvements | 实验评估与改进建议

After obtaining results, compare them with accepted values. Calculate the percentage difference or percentage error to quantify how reliable the experiment was. A systematic error cannot be reduced by repetition, so suggest ways to eliminate it, such as using a calibrated sensor.

获得结果后，将其与公认值进行比较。计算百分差或百分误差以量化实验的可靠程度。系统误差无法通过重复来减小，因此要提出消除它的方法，例如使用经过校准的传感器。

Identify the main sources of uncertainty. For a cooling curve, heat loss to the surroundings is a significant factor; using a lid and a vacuum flask can improve the design. Always comment on whether the measuring instruments were adequate.

识别主要的误差来源。对于冷却曲线，热量向周围散失是一个重要因素；使用盖子和真空瓶可以改进实验设计。始终评论测量仪器是否足够。

When suggesting an improvement, be specific. Instead of saying ‘use more accurate equipment’, state ‘use a digital vernier caliper with a resolution of 0.01 mm instead of a metre rule’ or ‘increase the mass used to reduce the percentage uncertainty in the extension measurement’.

提出改进建议时要具体。不要说“使用更精确的设备”，而要说“使用分辨率为 0.01 mm 的数显游标卡尺代替米尺”或“增大所用质量以减小伸长量测量的百分百不确定度”。

10. Exam Tips for Practical Assessments | 考试技巧与常见陷阱

Read the entire question before starting the experiment. It often contains crucial information on the expected graph shape or the number of significant figures required. Plan how you will manage your time across the different sections.

开始实验前通读整个题目。题目常包含关于预期图形形状或所需有效数字位数的关键信息。提前规划如何在不同部分之间分配时间。

In Alternative-to-Practical papers, you may be asked to describe how to avoid parallax error. The standard answer is: ‘Place the eye perpendicular to the scale’ or ‘use a set square to align the eye with the pointer’. Never just say ‘read the scale carefully’.

在实验替代试卷中，你可能会被要求描述如何避免视差误差。标准答案是：“将视线垂直对准刻度尺”或“使用三角尺使视线与指针对齐”。切勿只说“仔细读取刻度”。

When drawing a graph, use a sharp pencil and check for anomalous points before drawing the best-fit line. If a point lies far off the line, circle it and consider repeating that measurement. Do not force the line through all points.

绘制图表时，用削尖的铅笔，在画最佳拟合线之前检查有无异常点。如果某点远离拟合线，圈出它并考虑重测该数据。不要强行使直线通过所有点。

For calculations, show all working, including formula substitution. The final answer should be given to a sensible number of significant figures, usually 2 or 3, matching the least precise measurement. Include the correct unit.

计算时要展示所有步骤，包括代入公式。最终答案的有效数字位数应合理，通常为 2 或 3 位，与最不精确的测量值保持一致。要写明正确的单位。

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