📚 AS Physics Unit 1 Jan19 Mark Scheme: Practical Investigation | AS物理单元1 2019年1月评分标准：实验探究
Understanding how examiners award marks for practical investigations is the key to reaching higher grades in AS Physics. The January 2019 Unit 1 mark scheme reveals exactly what is expected in questions on experimental design, data handling, graph work, uncertainty analysis and evaluation. This article walks you through a typical resistivity experiment, aligning every step with the precise requirements of the jan19 mark scheme.
理解考官如何为实验探究打分，是AS物理获取高分的关键。2019年1月单元1的评分标准清楚揭示了实验设计、数据处理、绘图、不确定度分析和实验评估等方面的具体要求。本文将以一个典型的电阻率实验为例，逐一对照jan19评分标准的细节，帮助你精准把握得分点。
1. The Role of the Mark Scheme in Practical Questions | 评分标准在实验题中的作用
The mark scheme is not just a list of correct answers; it defines acceptable wording, the number of significant figures, tolerance ranges for measurements, and how marks are allocated to graph plotting, uncertainty calculations and evaluation. For AS Unit 1 (WPH11/01), a significant proportion of the paper tests practical skills through written questions based on familiar experiments.
评分标准不仅仅是正确答案的列表，它定义了可接受的表述、有效数字的位数、测量值的容差范围，以及绘图、不确定度计算和评估部分的给分方式。在AS单元1(WPH11/01)中，相当一部分题目通过基于熟悉实验的书面问题来考查实践技能。
2. The Jan19 Resistivity Investigation at a Glance | Jan19电阻率实验概览
In the January 2019 paper, students were given data from an experiment to determine the resistivity of a metal wire. A micrometer was used to measure the diameter, a meter rule to measure the length, and a circuit with a voltmeter and ammeter to find the resistance for different lengths. Candidates had to complete a table, plot a graph of resistance R against length L, determine the gradient, calculate resistivity and evaluate uncertainties.
在2019年1月的试卷中，考生需要根据一个测定金属丝电阻率的实验所给数据进行分析。实验使用了千分尺测量直径，米尺测量长度，利用电压表和电流表电路测得不同长度下的电阻。考生需完成数据表，绘制电阻R与长度L的关系图，求斜率，计算电阻率并评估不确定度。
3. Measurements and Instrument Precision | 测量与仪器精度
Diameter readings must be taken at several points along the wire using a micrometer screw gauge, which reads to 0.01 mm. The mark scheme requires the diameter to be recorded to at least 0.01 mm and a mean value calculated. For length, a metre rule reads to 1 mm, so all length readings should be given to the nearest mm. All raw data must have consistent precision.
直径必须使用千分尺在导线不同位置多次测量，千分尺读数为0.01 mm。评分标准要求直径至少记录到0.01 mm，并计算平均值。对于长度，米尺最小刻度为1 mm，因此所有长度读数应精确到毫米。所有原始数据必须具有一致的精度。
4. Tables and Significant Figures | 结果表格与有效数字
The mark scheme expects each column heading to include the quantity and its unit, divided by a solidus, e.g. 'R / Ω'. All calculated values in the table must be given to the same number of significant figures, typically three. The data in the table below illustrates the correct format.
评分标准要求每一栏的表头包含物理量和单位，并用斜线分隔，例如“R / Ω”。表中所有计算值必须具有相同的有效数字位数，通常为三位。下表以正确格式展示了数据。
| L / m | V / V | I / A | R / Ω |
|---|---|---|---|
| 0.200 | 0.45 | 0.22 | 2.05 |
| 0.400 | 0.89 | 0.22 | 4.05 |
| 0.600 | 1.34 | 0.22 | 6.09 |
| 0.800 | 1.78 | 0.22 | 8.09 |
| 1.000 | 2.22 | 0.22 | 10.1 |
Notice how the resistance values are given to three significant figures, matching the precision of the voltmeter and ammeter readings. The mark scheme penalises inconsistent significant figures or missing units in the header.
注意电阻值都给出了三位有效数字，与电压表和电流表读数的精度相匹配。评分标准会对有效数字不一致或表头缺少单位的情况扣分。
5. Plotting the Graph and Error Bars | 绘图与误差棒
Axes must be labelled with quantity and unit, using a clear linear scale that occupies more than half the graph paper. Points are plotted accurately as small crosses. The mark scheme from jan19 required error bars on the resistance values to represent the uncertainty from the voltmeter and ammeter. The absolute uncertainty in R was often calculated using percentage uncertainties from V and I.
坐标轴必须标明物理量和单位，并采用清晰的线性刻度，使图形占据坐标纸的一半以上。数据点以小的×准确标出。jan19的评分标准要求电阻值上添加误差棒，以表示电压表和电流表带来的不确定度。R的绝对不确定度通常通过V和I的百分不确定度合成计算。
ΔR = R × (ΔV/V + ΔI/I)
ark specifically for correct error bars. If the uncertainty is very small, the candidate may state that the error bars are negligible but still must indicate this on the graph or in the write-up.
然后绘制竖直误差棒表示±ΔR。评分标准对正确的误差棒有专门赋分。如果不确定度非常小，考生可以指出误差棒可以忽略，但仍需在图上或文字说明中注明。
6. Determining Gradient and Intercept | 计算斜率和截距
. The jan19 mark scheme requires the use of a large triangle to calculate the gradient, with coordinates read to the precision of the graph grid. The gradient must have the correct unit, Ω m⁻¹.
R-L图应得到一条过原点的直线，验证关系式R = (ρ/A)L。jan19评分标准要求使用大三角形计算斜率，坐标读数精度需与坐标纸网格匹配。斜率必须带上正确单位Ω m⁻¹。
gradient = ΔR / ΔL
If a best-fit line and a worst-fit line are drawn, the mark scheme may ask for the gradient of both to estimate uncertainty. Always show the triangle’s rise and run directly on the graph, as it is an explicit marking point.
如果绘制了最佳拟合线和最差拟合线，评分标准可能要求利用两者的斜率来估算不确定度。务必在图上直接标出三角形的纵向增量与横向长度，这是一个明确的得分点。
7. Calculating Resistivity and Its Units | 计算电阻率及单位
The mark scheme expects the substitution to be clear, the value of ρ to be given in Ω m, and the final answer quoted to an appropriate number of significant figures, often two or three.
一旦求得斜率m，电阻率ρ可由ρ = m × A求得，其中A为横截面积。A由平均直径d计算：A = πd²/4。评分标准要求清楚展示代换过程，电阻率的值以Ω m为单位，最终答案的有效数字位数要合理，通常为两到三位。
ρ = m × (πd²/4)
10⁻⁴)² / 4 = 5.73 × 10⁻⁸ m². With m = 10.1 Ω m⁻¹, ρ = 10.1 × 5.73 × 10⁻⁸ ≈ 5.8 × 10⁻⁷ Ω m.
如果d = 0.27 mm = 2.7 × 10⁻⁴ m，则A = π × (2.7 × 10⁻⁴)² / 4 = 5.73 × 10⁻⁸ m²。取m = 10.1 Ω m⁻¹，得ρ = 10.1 × 5.73 × 10⁻⁸ ≈ 5.8 × 10⁻⁷ Ω m。
8. Percentage Uncertainty and Comparison with Standard Value | 百分不确定度与标准值比较
entage uncertainty in the gradient (from worst-fit line) and twice the percentage uncertainty in diameter (since area depends on d²). You must then compare your result with the accepted value, e.g. 4.9 × 10⁻⁷ Ω m for constantan, and comment on accuracy using percentage difference.
jan19评分标准经常对电阻率的百分不确定度计算设分。一般通过合成斜率的百分不确定度（来自最差拟合线）和直径的百分不确定度的两倍（因为面积取决于d²）求得。然后需将实验结果与认可值（如康铜的4.9 × 10⁻⁷ Ω m）比较，利用百分差评述准确度。
%U(ρ) = %U(m) + 2 × %U(d)
The percentage difference is calculated as |ρ_exp - ρ_standard| / ρ_standard × 100% mental uncertainty, the result is considered accurate within the limits of the experiment.
百分差 = |ρ实验 - ρ标准| / ρ标准 × 100%。若百分差落在实验不确定度范围内，则结果被认为在实验限度内是准确的。
9. Sources of Error and Their Impact | 误差来源及其影响
The mark scheme accepts zero errors from the micrometer, parallax errors when reading the metre rule, heating effects causing resistance drifts, and contact resistance at crocodile clips. Each must be linked to the quantity affected. For instance, a zero error in the micrometer would systematically shift all diameter readings, leading to a wrong A and hence an inaccurate ρ.
评分标准接受千分尺的零误差、米尺读数时的视差、热效应引起的电阻漂移，以及鳄鱼夹处的接触电阻。每个来源必须与所影响的物理量相关联。例如，千分尺的零误差会系统性地偏移所有直径读数，导致错误的A，进而使ρ不准确。
Heating of the wire increases resistance, causing points at larger currents to deviate upwards, reducing the gradient’s reliability. Keeping current low and taking readings quickly are valid improvements highlighted in mark schemes.
导线发热会增加电阻，使较大电流下的数据点向上偏离，降低斜率的可靠性。保持小电流并快速读取数据是评分标准中认可的有效改进措施。
10. Evaluation and Suggested Improvements | 实验评估与改进建议
Candidates are expected to identify the largest source of uncertainty and suggest a practical refinement. The jan19 mark scheme rewarded replacing the metre rule with a travelling microscope for length measurement to reduce parallax and reading uncertainty. Alternatively, using a micrometer with a ratchet to minimise zero errors and measuring diameter in multiple orientations adds credit.
考生需要指出最大不确定度来源并提出实际改进。jan19评分标准对使用游标显微镜替代米尺测量长度以减少视差和读数不确定度予以给分。另外，使用带棘轮的千分尺以减小零误差，并在多个方向测量直径也能加分。
Other improvements may include using a constant temperature bath to stabilise the wire, or using a digital ohmmeter to measure resistance directly, although the latter changes the experimental method. Evaluation must always discuss why the change improves accuracy.
其他改进可能包括恒温浴槽稳定导线温度，或使用数字欧姆表直接测量电阻，尽管后者改变了实验方法。评估时必须讨论为何这种改变能提高准确度。
11. Common Mistakes Highlighted in the Jan19 Mark Scheme | Jan19评分标准中强调的常见错误
Many candidates lost marks by plotting R against 1/L or failing to check that the graph line passed through the origin. Others used an incorrect formula for area, forgetting the factor ¼. The mark scheme also penalised missing error bars, inconsistent significant figures in final answers, and omitting units on graph axes and in the gradient value.
许多考生因绘制了R-1/L图，或未能检查图线是否通过原点而失分。也有考生面积公式使用错误，漏掉了1/4因子。评分标准还对缺少误差棒、最终答案有效数字不一致，以及坐标轴和斜率值缺少单位等情况扣分。
In the uncertainty calculation, a typical error was forgetting to double the percentage uncertainty in diameter. Another was using the difference between best and worst gradient without converting to a percentage. These subtle points are clearly specified in the jan19 mark scheme.
在不确定度计算中，典型错误是忘记将直径的百分不确定度翻倍。另一错误是直接使用最佳与最差斜率之差而忘转换为百分数。这些细微的得分点在jan19评分标准中都有明确指示。
12. Key Strategies to Maximise Your Score | 提升分数的关键策略
able in first column, dependent variable in later columns, all with correct units. Before plotting, check the scale so your graph covers at least 6×8 large squares. Draw error bars first, then find the best-fit line using a transparent ruler.
答题时首先明确哪个量是被测变量，哪个量是改变量。采用评分标准要求的表格结构：自变量在第一列，因变量在其后，所有带有正确单位。绘图前检查刻度，确保图形占用至少6×8大格。先画误差棒，再用透明尺作最佳拟合线。
For uncertainty, always start from the instrument precision or repeat readings. Use worst-fit lines to find uncertainty in gradient, and combine contributions correctly. Finally, in evaluation, suggest improvements that directly address the major uncertainty you have identified, using scientific language and explaining the underlying physics.
处理不确定度时，始终从仪器精度或重复读数出发。利用最差拟合线求斜率的不确定度，并正确合成各项贡献。最后，在评估部分，针对你确认的主要不确定度提出改进建议，使用科学语言并解释背后的物理原理。
Practising with past papers and corresponding mark schemes is the most effective way to internalise these expectations. The jan19 paper remains an excellent resource to see how examiners think.
利用历年真题和对应评分标准进行练习，是内化这些要求的最高效方式。jan19试卷是了解考官思维方式的绝佳资源。
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