PH03 Experimental Investigation: A Complete Guide | PH03 实验探究完全指南

📚 PH03 Experimental Investigation: A Complete Guide | PH03 实验探究完全指南

Success in Unit 3 (PH03) of Edexcel International A Level Physics hinges on your ability to design, execute, and evaluate experiments with precision. This guide breaks down the essential skills required to tackle practical investigation questions, from initial planning to drawing evidence-based conclusions. By mastering these techniques, you will be well-prepared to analyse data, quantify uncertainties, and critically assess experimental methods.

要在爱德思国际 A Level 物理第三单元 (PH03) 中取得成功，关键在于精准设计、实施和评估实验的能力。本指南详细解析了应对实验探究题所需的各项核心技能，从最初的计划制定到基于证据得出结论。通过掌握这些技巧，你将能够熟练分析数据、量化不确定度，并批判性地评价实验方法。

1. Understanding the Question and Planning | 理解问题与制定计划

Carefully deconstruct the investigation brief. Identify the independent variable you will change, the dependent variable you will measure, and all other variables that must be kept constant to ensure a fair test. Draft a step-by-step procedure that is clear, repeatable, and minimises hazards.

认真拆解探究任务。明确你要改变的自变量、要测量的因变量，以及所有必须保持恒定的其他变量，以确保实验公平。草拟一个步骤清晰、可重复且能最大限度减少危险的实验方案。

• Highlight the apparatus needed and justify why specific instruments (e.g., a micrometer instead of a ruler) are chosen.
• 标注所需的仪器，并解释为什么选择特定工具（例如用千分尺而不是直尺）。
• Plan how to vary the independent variable over a suitable range, ensuring sufficient data points for reliable analysis (typically 6–8 readings).
• 规划如何在合适范围内改变自变量，确保获取足够的数据点以进行可靠分析（通常6–8组读数）。
• Describe how you will maintain control variables, such as keeping temperature constant by avoiding direct sunlight or using a water bath.
• 说明如何维持控制变量，例如通过避免阳光直射或使用水浴保持温度恒定。

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2. Variables and Controls | 变量与控制

A physics investigation demands rigorous control of extraneous factors. Besides naming independent and dependent variables, you must explain how each control variable is monitored and held fixed. For example, in a free-fall experiment to determine g, the drop height is the independent variable, the time of fall is the dependent variable, and the mass of the ball, shape, and release mechanism must be controlled.

物理探究要求严格控制无关因素。除了指出自变量和因变量，你还必须说明如何监测并固定每一个控制变量。例如，在测定重力加速度 g 的自由落体实验中，下落高度是自变量，下落时间是因变量，而小球质量、形状和释放机制都必须加以控制。

Type of Variable | 变量类型	Example in Ohm’s law experiment | 欧姆定律实验示例	Control method | 控制方法
Independent	Potential difference V across resistor	Adjust power supply in small increments
Dependent	Current I through the circuit	Read ammeter precisely
Control	Temperature of resistor	Switch off between readings to let it cool

Identifying plausible sources of error early helps you design a procedure that reduces their impact, such as taking repeat measurements to minimise random errors or shielding from draughts.

尽早识别可能的误差来源有助于设计出减少其影响的操作程序，例如重复测量以尽量减少随机误差，或屏蔽气流干扰。

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3. Apparatus Selection and Justification | 仪器选择与理由

Your choice of measuring instruments directly affects the precision of results. When listing apparatus, state the resolution (smallest increment) and connect it to the percentage uncertainty. For length measurements, a vernier caliper (±0.1 mm) or micrometer (±0.01 mm) is superior to a metre rule (±1 mm) for small dimensions.

测量仪器的选择直接影响结果的精密度。列出仪器时，要说明其分辨率（最小刻度），并将其与百分比不确定度联系起来。对于长度测量，游标卡尺（±0.1毫米）或千分尺（±0.01毫米）在测量小尺寸时优于米尺（±1毫米）。

Justify every piece of equipment. For instance, a digital sensor and data logger can record rapid changes (e.g., temperature, light intensity) with high frequency, eliminating human reaction time uncertainty. Explain why a particular range or sensitivity is necessary for the expected values.

对每一件设备进行论证。例如，数字传感器和数据记录仪可以高频率记录快速变化（如温度、光强），消除人体反应时间的不确定度。解释为什么对于预期数值需要特定的量程或灵敏度。

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4. Safety Considerations | 安全注意事项

Examiners expect clear safety statements, not generic ones. Link hazards directly to the experiment. If using an oscilloscope or power supply, mention checking insulation and keeping voltages below safe limits (e.g., ≤ 12 V for basic circuit work). For dynamics experiments, secure masses to prevent them from dropping onto feet.

考官期望看到具体的安全说明，而非泛泛而谈。将危险与实验直接关联起来。如果使用示波器或电源，要提到检查绝缘情况并使电压保持在安全限值以下（例如，基础电路实验中使用 ≤ 12 伏）。对于动力学实验，要固定好重物防止其掉下砸伤脚。

• Describe how to handle heavy or falling objects: use a crash mat or clamp stand firmly.
• 描述如何处理重物或坠落物：使用缓冲垫或将支架牢牢固定。
• Mention electrical safety: avoid water near circuits, use low-voltage sources, and check wires for fraying.
• 提及电气安全：远离水源使用电路、采用低压电源、检查导线是否磨损。
• When heating substances, wear goggles and use heatproof mats; never heat a sealed container.
• 加热物质时，佩戴护目镜并使用隔热垫；切勿加热密闭容器。

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5. Data Collection Techniques | 数据收集技术

Collect data methodically to reduce random errors. For each value of the independent variable, take at least three repeated measurements of the dependent variable and calculate the mean. This practice reveals anomalies and improves reliability. Record raw data immediately in a prepared table with correct headings and units.

有条不紊地收集数据以减少随机误差。对于自变量的每一个取值，至少对因变量进行三次重复测量并计算平均值。这种做法能揭示异常值并提高可靠性。立即将原始数据记录在预先设计好的表格中，表头要包括正确的单位和物理量名称。

When using a stopwatch, measure time for multiple oscillations (e.g., 20 oscillations) and then divide to find the period. This technique reduces the percentage uncertainty from human reaction time. Always state how you will minimise parallax error when reading scales, such as by viewing the needle perpendicularly or using a digital display.

使用秒表时，测量多个周期（如20个周期）的时间再除以次数得到周期。这种技术可降低由人体反应时间引起的百分比不确定度。始终说明在读取刻度时如何减少视差，例如垂直观察指针或使用数字显示。

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6. Recording Results and Observations | 记录结果与观察

A well-structured results table is crucial. It must include columns for all raw measurements, calculated means, and any derived quantities. Headings should be in the format ‘Quantity / unit’, e.g., ‘Length l / cm’ and ‘Potential difference V / V’. Record values to the same number of decimal places consistent with the instrument’s precision.

结构清晰的记录表格至关重要。表格必须包含所有原始测量值、计算的均值以及任何导出量的列。表头应采用“物理量 / 单位”的格式，例如“长度 l / cm”和“电势差 V / V”。记录数值的小数位数应与仪器的精密度保持一致。

If you observe qualitative changes (colour shift, sparking, sound), note them in a separate observation column. These can later help explain anomalies in the data. Indicate uncertainties directly in the table, e.g., ‘± 0.01 cm’ for micrometer readings.

若观察到定性变化（颜色变化、火花、声音），务必在单独的观察栏中记录。这些信息后续可帮助解释数据中的异常。直接在表格中注明不确定度，例如对于千分尺读数可标注“± 0.01 cm”。

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7. Analysing Data: Graphs and Calculations | 数据分析：图表与计算

Plotting a graph is the most effective way to reveal relationships between variables. Choose scales that use more than half the graph grid in both directions and label axes with quantity and unit. Draw a best-fit line (straight or smooth curve) that passes through as many points as possible, with equal numbers of points above and below the line. Always calculate gradient and intercept when a linear relationship is expected.

绘制图表是揭示变量间关系的最有效方法。选择坐标轴比例时，应使数据点占据网格纸一半以上的空间，并标明物理量和单位。画一条最合适的直线或平滑曲线，尽可能通过多的点，并使线上、线下的点数大致相等。当预期为线性关系时，一定要计算斜率和截距。

Use the relationship defined by the physics equation to determine unknown quantities. For example, if the period T of a pendulum is given by T = 2π√(l/g), then plotting T² against l yields a straight line with gradient = 4π²/g. State clearly how you use the gradient or intercept to find the required value, and perform all calculations step by step.

利用物理方程定义的关系来确定未知量。例如，单摆周期 T = 2π√(l/g)，绘制 T² 对 l 的图像得到一条斜率为 4π²/g 的直线。请清晰说明如何使用斜率或截距来求出所需值，并逐步完成所有计算。

gradient = Δy / Δx = (y₂ − y₁) / (x₂ − x₁)

斜率 = Δy / Δx = (y₂ − y₁) / (x₂ − x₁)

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8. Uncertainty and Error Analysis | 不确定度与误差分析

Every measurement has an uncertainty. For a single reading instrument (e.g., metre rule), the absolute uncertainty is half the smallest scale division. For digital instruments, it is the smallest displayed digit. When two measurements are taken to find a difference (e.g., initial and final length), the uncertainty doubles. Combine uncertainties using appropriate rules when calculating derived quantities.

每个测量值都有不确定度。对于单次读数仪器（如米尺），绝对不确定度是最小刻度的一半。对于数字仪器，等于最后一位显示数字的一个单位。当需要两次测量来求差值时（如初末长度），不确定度加倍。在计算导出量时，使用合适的规则来合成不确定度。

Operation | 运算	Rule for combining uncertainties | 组合规则
Addition / Subtraction | 加减法	Add absolute uncertainties: Δ(a+b) = Δa + Δb
Multiplication / Division | 乘除法	Add percentage (or fractional) uncertainties
Power | 幂运算	Multiply the percentage uncertainty by the power n

Calculate the percentage uncertainty in the mean of repeated readings by using half the range (max − min)/2 as the absolute uncertainty. Compare the percentage uncertainty of your final result with a target (often ± 5%) to judge quality. Always express the final answer to an appropriate number of significant figures, matching the least precise measurement used in the calculation.

计算重复读数平均值的百分比不确定度时，用半极差（最大值 – 最小值）/2 作为绝对不确定度。将最终结果的百分比不确定度与目标值（通常为 ± 5%）比较，以判断实验质量。最终答案的有效数字位数应与计算中使用的最不精确的测量值保持一致。

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9. Evaluating the Experiment | 实验评估

Evaluation goes beyond listing errors; you must distinguish between systematic and random errors, explain their effect on the result, and suggest realistic improvements. Systematic errors (e.g., zero error on a caliper, incorrectly calibrated sensor) shift all readings in one direction and can be detected by comparing with a known standard or by intercept analysis on a graph.

实验评估不仅仅是罗列误差；你必须区分系统误差和随机误差，解释它们对结果的影响，并提出切实的改进建议。系统误差（如卡尺的零位误差、传感器校准错误）会使所有读数朝同一方向偏移，可以通过与已知标准比较或通过图像截距分析来检测。

Random errors (parallax, timing variations) cause scatter about the true value. Their effect is reduced by averaging many readings. If the line of best fit does not pass through the theoretical intercept, identify the likely cause: e.g., a non-zero y-intercept in a V vs I graph may indicate contact resistance in the circuit or a non-ohmic component. Suggest specific improvements, such as using a low-resistance wire or cleaning terminals.

随机误差（视差、计时波动）导致数据点围绕真值散布。其影响可通过多次读数取平均来减小。如果最佳拟合线不通过理论截距，要找出可能原因：例如，V-I 图像出现非零截距可能表明电路中有接触电阻或使用了非欧姆元件。提出具体的改进建议，如使用低电阻导线或清洁接线端子。

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10. Drawing Conclusions | 得出结论

Your conclusion must directly reference the data and the gradient/equation where relevant. State whether the experimental value agrees with the accepted value within the limits of uncertainty. For instance, “The measured value of resistivity ρ = (1.12 ± 0.05) × 10⁻⁶ Ω m aligns with the accepted value of 1.10 × 10⁻⁶ Ω m within experimental uncertainty.”

结论必须直接引用数据和相关斜率/方程。表述实验值在不确定度范围内是否与公认值相符。例如，“测得的电阻率 ρ = (1.12 ± 0.05) × 10⁻⁶ Ω m 与公认值 1.10 × 10⁻⁶ Ω m 在实验不确定度范围内一致。”

If there is a discrepancy, quantify it as a percentage difference and suggest which systematic or random errors are most likely responsible. Always link your conclusion back to the aim of the investigation and the physics principles involved. Even if the results are far from ideal, a well-reasoned explanation of why that happened earns high marks.

如果存在偏差，用量化的百分比差异来说明，并指出最可能由哪些系统或随机误差造成。始终将结论回扣至探究目标和所涉及的物理原理。即使结果远不理想，对偏差原因的合理解释也能获得高分。

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11. Common Experiments and Key Equations | 常见实验与关键方程

Many PH03 investigations revolve around core practicals. Know the underlying equation and the graph you are required to plot:

许多 PH03 实验探究都围绕核心实验展开。请掌握基础方程和理解所需绘制的图像：

Experiment | 实验	Key relationship | 关键关系	Graph | 图像
Determining g by free fall	h = ½ g t²	h against t² → slope = ½ g
Young’s modulus of a wire	E = (F L) / (A ΔL)	F against ΔL → slope for E
Resistivity of a metal wire	R = ρ L / A	R against L → slope = ρ / A
Internal resistance and EMF	V = ε − I r	V against I → intercept = ε, |slope| = r
Simple harmonic motion (mass-spring)	T = 2π√(m/k)	T² against m → slope = 4π²/k

For each setup, be ready to identify the main sources of uncertainty and the steps you would take to minimise them. Practice determining intercepts and interpreting their physical meaning—it is often the key to solving the investigation question.

对于每一种装置，要能识别主要的不确定度来源以及你将采取的减小措施。练习确定截距并解读其物理意义——这往往是解决探究题的关键。

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12. Final Tips for the PH03 Paper | PH03 试卷终极提示

Time management is vital. Spend a few minutes planning before you write, especially for the design question. Always show your working for uncertainty calculations—clear method steps earn method marks even if the final number is off. Use a sharp pencil for graphs, and draw lines with a ruler. After finishing, check that every component of the question has been addressed, including safety, control variables, and a justified conclusion.

时间管理至关重要。动笔之前花几分钟做计划，尤其是在设计题上。不确定度计算一定要展示过程——即使最终数字不对，清晰的方法步骤也能拿到方法分。用削尖的铅笔绘制图表，并用直尺画线。完成后，检查是否回答了问题的每个部分，包括安全措施、控制变量和有依据的结论。

Remember that PH03 tests your practical thinking as much as your content knowledge. Explain your reasoning at every stage—why you chose an instrument, why a particular graph is plotted, why an anomalous point was discarded. This structured approach transforms a good answer into an excellent one.

记住，PH03 不仅考察你的知识内容，也考验你的实验思维。在每个阶段解释你的推理——为什么选择这个仪器，为什么绘制这种图像，为什么某个异常点被舍弃。这种结构化的方法能让一个优秀答案更加出色。

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