Decoding the 2016 IAL Physics Unit 1 Experimental Investigation Mark Scheme | 解读2016年国际AS物理单元1实验探究评分方案

📚 Decoding the 2016 IAL Physics Unit 1 Experimental Investigation Mark Scheme | 解读2016年国际AS物理单元1实验探究评分方案

The experimental investigation in Edexcel International AS Physics Unit 1 (9630-PH01) is a high-stakes section that tests a candidate’s ability to think like a real scientist. Mark schemes from past papers, such as the 2016 examination, reveal exactly what examiners are looking for: precise control of variables, considered error analysis, intelligent graph plotting and a deep evaluation of the experiment. This article dissects those key marking points using a classic free-fall experiment to determine g, so you can secure the top marks in your own investigation questions.

在爱德思国际AS物理单元1（9630-PH01）中，实验探究是一个高比重部分，考查考生像真正的科学家一样思考的能力。从历年真题的评分方案——比如2016年的考试——可以清晰地看到考官究竟在寻找什么：对变量的精确控制、周密的误差分析、规范的图表绘制以及对实验的深度评估。本文将以一个经典的测定重力加速度g的自由落体实验为例，逐一剖析这些关键得分点，帮助你在实验探究题中稳拿高分。

1. The Role of the Experimental Investigation in PH01 | 实验探究在PH01中的作用

The final question on the Unit 1 paper is typically an extended experimental design or analysis task, worth a substantial number of marks. In the 2016 series, this question asked students to plan or interpret an investigation into free fall. The mark scheme rewards not just correct answers, but a systematic scientific approach: clear identification of variables, a logical method, appreciation of uncertainties, and the ability to comment on the reliability of the result.

单元1试卷的最后一道大题通常是扩展性的实验设计或分析任务，分值很高。在2016年的考试中，这道题要求学生设计或解读一个自由落体实验。评分方案不仅奖励正确答案，更奖励系统的科学方法：清晰地识别变量、逻辑性强的步骤、对不确定度的重视，以及评价结果可靠性的能力。

2. Understanding the Exam Context: Free Fall Investigation | 理解考试背景：自由落体探究

In the 2016 investigation, a small steel sphere was released from an electromagnet and allowed to fall vertically onto a trapdoor switch. The timer started when the circuit to the electromagnet was broken, and stopped when the sphere hit the trapdoor. Students were required to vary the height h and measure the time of fall t. The relationship h = ½ g t² was then used to determine g from a straight-line graph.

在2016年的探究中，一个小钢球从电磁铁释放，垂直下落到一个陷门开关上。当电磁铁电路断开时计时器开始计时，小球撞击陷门时计时停止。考生需要改变下落高度h并测量下落时间t，然后利用关系式h = ½ g t²，通过一条直线图来测定g。

h = ½ g t²

The mark scheme shows that a graph of h against t² must be plotted, where the gradient equals ½ g. Hence, g = 2 × gradient. Examiners expected candidates to explain that a graph of h vs t would be a curve, and why a straight-line graph is more reliable for determining a constant.

评分方案表明，必须绘制h-t²图，其斜率等于½ g，因此g = 2 × 斜率。考官希望考生能解释h-t图是一条曲线，而直线图对于确定一个常数来说更加可靠。

3. Identifying and Controlling Variables | 识别和控制变量

Marks are allocated for correctly stating the independent variable, dependent variable and control variables. In this investigation, the independent variable is the height h, the dependent variable is the time t (or t²), and key control variables include the mass of the sphere, its shape, and the location of the experiment. The mark scheme often rewards the mention that the sphere should be released from rest, not pushed, and that the same sphere must be used throughout to keep diameter and mass constant.

正确陈述自变量、因变量和控制变量可以得分。在这个实验中，自变量是高度h，因变量是时间t（或t²），关键的控制变量包括小球的质量、形状以及实验地点。评分方案常常奖励提到小球必须从静止释放，不能有初速度，并且全程使用同一个球以保持直径和质量不变。

Another critical control is the release mechanism: the current to the electromagnet must be switched off cleanly, and the sphere should not stick. Any magnetic remanence could introduce a delay, making measured t larger than the true free-fall time.

另一个关键的控制是释放机制：电磁铁的电流必须干净利落地切断，小球不能有粘连。任何剩磁都可能导致延时，使测量时间t大于真实自由落体时间。

4. Minimising Sources of Error | 减少误差来源

The 2016 mark scheme expects candidates to identify significant sources of systematic and random error. For a free-fall experiment, air resistance is often cited, but since a dense steel sphere is used, its effect is small. The dominant errors come from the measurement of height and the timing. Using a metre ruler, the height reading has a parallax uncertainty if the object’s base and the trapdoor surface are not aligned with the eye. The mark scheme rewards stating that a set square or a perpendicular viewing angle should be used.

2016年的评分方案期望考生能识别出系统误差和随机误差的主要来源。对于自由落体实验，空气阻力常被提到，但由于使用了密度大的钢球，其影响很小。主要的误差来自高度和时间的测量。使用米尺读取高度时，如果重物底部和陷门表面未与视线对齐，就会产生视差不确定度。评分方案奖励提出应使用直角尺或垂直视角进行测量。

Timing error arises from the reaction time of the experimenter if a stopwatch is used. The mark scheme highly prizes the use of an electronic timer or data logger triggered by the circuit break and the trapdoor switch. This eliminates human reaction time almost entirely, turning the error into a small instrumental uncertainty instead.

计时误差源于实验者的反应时间（如果使用秒表）。评分方案高度赞扬使用由电路断开和陷门开关触发的电子计时器或数据记录仪，这样几乎完全消除了人的反应时间，使误差仅变成很小的仪器不确定度。

5. Recording Data with Appropriate Precision | 以适当精度记录数据

Examiners look at the way data is presented in tables. In the 2016 mark scheme, marks are given for column headers that include the quantity and its unit separated by a slash, for example ‘h / m’ and ‘t / s’. Values must be recorded to the same number of decimal places, reflecting the precision of the measuring instrument. A metre ruler can measure to the nearest millimetre, so heights like 1.000 m should be recorded as 1.000 m, not 1 m. Similarly, an electronic timer recording to 0.01 s requires values such as 0.45 s, not 0.450 s if the precision is only 0.01 s (although careful reading of the instrument’s scale is needed).

考官会检查数据在表格中的呈现方式。在2016年的评分方案中，如果列标题包含了物理量及其单位、中间用斜线分隔，例如’h / m’和’t / s’，就可以得分。所有数值必须记录到相同的小数位数，反映测量仪器的精度。米尺可以测量到最接近的毫米，因此像1.000 m的高度应记录为1.000 m，而不是1 m。同样，一台精确到0.01 s的电子计时器要求数值如0.45 s，如果其精度仅为0.01 s，则不应写作0.450 s（但需要仔细读取仪器刻度）。

Repeating the timing measurement for each height and calculating a mean time is strongly rewarded. The spread of repeat readings gives a direct estimate of random uncertainty. The mark scheme accepts the range/2 or the standard deviation as a measure of this uncertainty for each t value.

对每个高度重复计时测量并计算平均时间会得到很高的评价。重复读数的分布范围直接给出了随机不确定度的估计。评分方案接受用极差除以2或标准偏差作为每个t值不确定度的量度。

h / m	t₁ / s	t₂ / s	t₃ / s	Mean t / s	t² / s²
0.500	0.32	0.31	0.33	0.32	0.10
1.000	0.45	0.46	0.44	0.45	0.20
1.500	0.55	0.56	0.54	0.55	0.30

This table illustrates how candidates should present data. The calculated t² column is required for the graph. Including a column for uncertainty in t, for example ±0.01 s, would further demonstrate best practice and can attract additional marks.

该表格展示了考生应如何呈现数据。计算出的t²列是绘图所必需的。如果再增加一列表示t的不确定度，例如±0.01 s，将进一步展示最佳实践，并可能获得额外加分。

6. Plotting a Graph and Choosing Axes | 绘制图表与选择坐标轴

A central part of the mark scheme is the quality of the graph. Candidates must plot h on the y-axis and t² on the x-axis, label axes with quantity and unit, use sensible linear scales that occupy more than half the graph paper, and plot points accurately. The 2016 scheme gives marks for small, neat crosses or encircled dots and the drawing of a single, straight line of best fit (not join-the-dots).

评分方案的核心部分是图表的质量。考生必须以h为纵轴、t²为横轴，坐标轴标明物理量和单位，使用能占据半张以上坐标纸的合理线性刻度，并精确描点。2016年的方案对使用小而整洁的叉号或圆圈标点、绘制一条单一的直线最佳拟合线（而非点对点连线）给予分数。

h = (g/2) t²

The relationship h = ½ g t² shows that the graph of h vs t² should be a straight line through the origin. In practice, small systematic errors (like the slight delay in the electromagnet release) may produce a small positive intercept on the h-axis. Examiners reward the identification and discussion of this intercept.

关系式h = ½ g t²表明，h-t²图应该是一条通过原点的直线。实际上，微小的系统误差（如电磁铁释放的轻微延迟）可能产生一个小的正截距。考官奖励对这个截距的识别和讨论。

7. Determining the Gradient and Intercept | 确定斜率和截距

The gradient calculation must use a large triangle on the best-fit line, not a pair of plotted data points. The mark scheme requires the coordinates of two well-separated points on the line to be read as accurately as possible, and the gradient calculated with the correct unit (m s⁻² in this case). The gradient equals ½ g, so doubling the gradient yields the experimental value of g. Candidates should round the final answer to an appropriate number of significant figures, typically 2 or 3, matching the precision of the input data.

斜率的计算必须使用最佳拟合线上的一个大三角形，而不是一对数据点。评分方案要求尽可能精确地读取线上两个相距较远的点的坐标，并计算出带有正确单位的斜率（此处为m s⁻²）。斜率等于½ g，因此将斜率乘以2即得到g的实验值。考生应将最终答案四舍五入到适当的有效数字位数，通常为2或3位，与原始数据的精度一致。

For the table above, taking points (0.10, 0.50) and (0.30, 1.50) on the line gives gradient = (1.50 – 0.50) / (0.30 – 0.10) = 1.00 / 0.20 = 5.0 m s⁻². This would imply g = 10.0 m s⁻², illustrating the type of calculation expected. A comment on comparing this with the accepted value (9.81 m s⁻²) would be required in the evaluation.

对于上表数据，取线上两点(0.10, 0.50)和(0.30, 1.50)，斜率 = (1.50 – 0.50) / (0.30 – 0.10) = 1.00 / 0.20 = 5.0 m s⁻²。这意味着g = 10.0 m s⁻²。这展示了期望的计算类型。在评估环节，还需要与公认值(9.81 m s⁻²)进行比较并加以评论。

8. Estimating Uncertainties in Measurements | 估计测量不确定性

The 2016 mark scheme expects a quantitative treatment of uncertainty. For the height measurement, the absolute uncertainty may be ±0.001 m or ±0.002 m as determined by the metre ruler and the difficulty in aligning the zero exactly with the bottom of the sphere. For time, the resolution of the electronic timer or half the range of repeat readings gives the absolute uncertainty. Candidates are rewarded for calculating the percentage uncertainty in t², noting that when a quantity is squared, its percentage uncertainty doubles.

2016年评分方案期望对不确定度进行定量处理。对于高度测量，绝对不确定度可能是±0.001 m或±0.002 m，这取决于米尺以及将零点与小球底部精确对齐的难度。对于时间，电子计时器的分辨率或重复读数范围的一半给出了绝对不确定度。考生如果能计算t²的百分比不确定度，并指出当一个量被平方时，其百分比不确定度会翻倍，将得到奖励。

If Δt = 0.01 s and mean t = 0.45 s, percentage uncertainty in t = (0.01/0.45) × 100% ≈ 2.2%.

如果Δt = 0.01 s，平均t = 0.45 s，则t的百分比不确定度 = (0.01/0.45) × 100% ≈ 2.2%。
Then percentage uncertainty in t² = 2 × 2.2% = 4.4%.

那么t²的百分比不确定度 = 2 × 2.2% = 4.4%。

Error bars representing the absolute uncertainty in t² can be added horizontally on the graph. The mark scheme allows the drawing of worst-fit lines (steepest and shallowest) to estimate the uncertainty in the gradient, which is then propagated to the final value of g. This level of detail distinguishes top candidates.

代表t²绝对不确定度的误差棒可以水平地添加在图上。评分方案允许绘制最差拟合线（最陡和最浅）来估计斜率的不确定度，然后传递到最终的g值。这种细节水平能区分出顶尖的考生。

9. Error Analysis and Percentage Difference | 误差分析与百分比差异

Once the experimental value of g has been found, the mark scheme asks candidates to calculate the percentage difference from the standard value 9.81 m s⁻². Using the earlier example of g = 10.0 m s⁻², the percentage difference is |10.0 – 9.81| / 9.81 × 100% ≈ 1.9%. If this percentage difference exceeds the estimated experimental percentage uncertainty, there is evidence of systematic errors.

一旦得到g的实验值，评分方案要求考生计算其与标准值9.81 m s⁻²的百分比差异。以上述g = 10.0 m s⁻²为例，百分比差异 = |10.0 – 9.81| / 9.81 × 100% ≈ 1.9%。如果这一差异超出了估计的实验百分比不确定度，就表明存在系统误差。

A strong candidate will then link systematic errors to specific features of the apparatus. For instance, if the measured g is too large, the time t might be consistently too small. This could happen if the trapdoor switch triggers slightly before the sphere actually hits, perhaps due to vibration. Conversely, a measured g that is too small suggests t is too large, often caused by residual magnetism delaying the release or by air resistance.

优秀的考生随后会将系统误差与仪器的具体特征联系起来。例如，如果测量的g偏大，说明时间t可能一贯偏小。如果陷门开关在小球实际撞击前就轻微触发（比如由于振动），就会出现这种情况。反过来，测量值偏小表明t偏大，通常是由剩磁延迟释放或空气阻力造成的。

10. Suggestions for Improvement and Further Investigations | 改进建议与进一步探究

The final part of the mark scheme rewards credible improvements that reduce identified errors. Using light gates instead of a mechanical trapdoor eliminates the bounce and switch-delay problems. A vacuum chamber would remove air resistance completely. Parallax errors in measuring h can be reduced by attaching a pointer to the bottom of the sphere and reading its position against a vertical scale, or by using a digital height gauge.

评分方案的最后一部分奖励那些能够减少已识别误差的合理改进建议。使用光电门代替机械陷门可以消除弹跳和开关延迟问题。真空室可以完全消除空气阻力。测量h的视差可以通过在小球底部安装一个指针，对照垂直刻度读数来降低，或者使用数字高度计。

Extending the investigation by changing the mass or material of the falling object allows discussion of the independence of g from mass, but this must be explained using the equation of motion, not simply stated. Dropping objects of different shapes could investigate the effect of air resistance, linking to terminal velocity concepts from later units. All these thoughtful extensions demonstrate higher-order scientific thinking and are strongly rewarded.

延伸探究，改变下落物体的质量或材料，可以讨论g与质量无关这一特性，但必须结合运动方程来解释，而不能只是陈述。释放不同形状的物体可以研究空气阻力的影响，这与后续单元中的终极速度概念相关联。所有这些深思熟虑的延伸都展示了高阶的科学思维，会受到高度奖励。

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Decoding the 2016 IAL Physics Unit 1 Experimental Investigation Mark Scheme | 解读2016年国际AS物理单元1实验探究评分方案