Year 13 WJEC Physics: Practical Assessment Key Points | Year 13 WJEC 物理：实验/实践考核要点

📚 Year 13 WJEC Physics: Practical Assessment Key Points | Year 13 WJEC 物理：实验/实践考核要点

Mastering practical skills is essential for success in Year 13 WJEC Physics. This guide covers the key experimental techniques, data handling, error analysis, graph work, and evaluation methods that are regularly assessed in written papers and practical endorsements.

掌握实验技能是 Year 13 WJEC 物理取得高分的关键。本指南涵盖在笔试和实验认可中经常考查的核心实验技术、数据处理、误差分析、图表绘制及评估方法。

1. Understanding Practical Assessment in WJEC Physics | 理解 WJEC 物理实验评估

In WJEC A2 Physics, experimental skills are assessed both through written exam questions and the Practical Endorsement. The assessment objectives test your ability to plan experiments, use apparatus, collect and analyse data, and evaluate procedures in terms of accuracy, precision, and sources of error.

在 WJEC A2 物理中，实验技能通过笔试题和实验认可进行评估。考查目标包括：规划实验、使用仪器、收集分析数据，以及从准确性、精密度和误差来源等方面评估实验程序。

Typical question formats include describing how to measure a quantity, drawing circuit diagrams, calculating uncertainties, plotting graphs, and suggesting improvements to a student’s method.

典型题型包括描述如何测量某个物理量、画出电路图、计算不确定度、绘制图表，以及对学生的实验方案提出改进建议。

2. Essential Measuring Instruments and Their Precision | 必备测量仪器及其精密度

You must know the typical precision of common instruments. A metre ruler has a precision of ±1 mm, a vernier caliper ±0.1 mm, a micrometer screw gauge ±0.01 mm, a digital stopwatch ±0.01 s (but reaction time is ~0.1–0.3 s), a voltmeter or ammeter typically ±0.01 V or ±0.01 A for digital, and a thermometer ±0.5 °C. Always record measurements to the resolution of the instrument unless limited by something else.

你需要熟悉常见仪器的典型精密度。米尺精密度为 ±1 mm，游标卡尺 ±0.1 mm，千分尺 ±0.01 mm，数字秒表 ±0.01 s（但反应时间约为 0.1–0.3 s），电压表或电流表（数字式）通常为 ±0.01 V 或 ±0.01 A，温度计 ±0.5 °C。除非受其他因素限制，否则应按仪器分辨率记录测量值。

Instrument	Typical Precision	Example Reading
Metre ruler	±1 mm	0.365 m or 365 mm
Vernier caliper	±0.1 mm	12.3 mm
Micrometer	±0.01 mm	4.52 mm
Digital multimeter	±(0.5% + 1 digit)	1.52 V

For each instrument, be able to state how you would reduce parallax error (e.g., aligning the eye perpendicular to the scale) and take repeat readings to identify random errors.

对于每种仪器，要能说明如何减少视差（例如视线与刻度垂直），并通过重复读数来识别随机误差。

3. Types of Errors and Uncertainty | 误差类型与不确定度

Random errors cause readings to be scattered around the true value and can be reduced by taking multiple measurements and calculating a mean. Systematic errors (e.g., zero error, calibration drift) shift all readings in one direction and cannot be reduced by averaging; they must be identified and corrected or allowed for in the analysis.

随机误差使读数分散在真值周围，可通过多次测量取平均值来减小。系统误差（如零位误差、校准漂移）使所有读数朝同一方向偏移，无法通过取平均来消除；必须识别并修正，或在分析中予以考虑。

Distinguish between accuracy (closeness to the true value) and precision (spread of repeated measurements). A set of precise measurements may not be accurate if a systematic error is present.

区分准确度（与真值的接近程度）和精密度（重复测量结果的分散程度）。如果存在系统误差，一组精密度高的测量值也可能不准确。

The absolute uncertainty Δx is the range within which the true value is expected to lie. For a digital instrument, Δx is at least ± the smallest scale division; for an analogue instrument, it is ± half the smallest division.

绝对不确定度 Δx 是真值预计会落入的范围。对数字仪器，Δx 至少为 ±最小分度值；对模拟仪器，则为 ±最小分度值的一半。

4. Calculating and Combining Uncertainties | 不确定度的计算与合成

Percentage uncertainty = (Δx / x) × 100%. This is useful when combining measurements. For sums or differences, absolute uncertainties add: if Z = A + B or Z = A – B, then ΔZ = ΔA + ΔB.

百分不确定度 = (Δx / x) × 100%。这在合成测量值时非常有用。对于和或差，绝对不确定度相加：若 Z = A + B 或 Z = A – B，则 ΔZ = ΔA + ΔB。

ΔZ = ΔA + ΔB (for Z = A ± B)

对于乘积或商，百分不确定度相加：若 Z = A × B 或 Z = A ÷ B，则 %ΔZ = %ΔA + %ΔB。若公式中含幂次，则乘以幂指数：若 Z = Aⁿ，则 %ΔZ = n × %ΔA。

%ΔZ = %ΔA + %ΔB (for Z = A × B or Z = A / B)

%ΔZ = n × %ΔA (for Z = Aⁿ)

Always calculate the uncertainty in a derived quantity and compare it with any expected precision. Be prepared to state which quantity contributes the greatest uncertainty to the result.

始终计算导出量的不确定度，并与预期精密度进行比较。要能指出哪个量对结果的贡献不确定度最大。

5. Recording Data with Appropriate Precision and Significant Figures | 以恰当的精密度和有效数字记录数据

Raw data should always be recorded to the resolution of the instrument. For example, a mass of 50 g measured on a balance reading to 0.1 g is written as 50.0 g. The number of significant figures in a calculated value must reflect the precision of the input data: the final result should be given to the same number of significant figures as the least precise measurement.

原始数据应始终按仪器分辨率记录。例如，用可读至 0.1 g 的天平测得 50 g 质量，应记录为 50.0 g。计算值有效数字的位数必须反映输入数据的精密度：最终结果的有效数字位数应与最不精确的测量值保持一致。

In tabulated results, maintain consistent decimal places or significant figures. Use column headings with units (e.g., ‘Current / A’, ‘Voltage / V’). Repeat readings help reduce random error and allow you to calculate a mean.

在表格结果中，要保持一致的小数位数或有效数字。表头应包含单位（例如“电流 / A”“电压 / V”）。重复读数有助于减小随机误差，并允许你计算平均值。

6. Plotting and Interpreting Graphs | 绘制和解读图表

Plot the independent variable on the x-axis and the dependent variable on the y-axis. Choose scales that use more than half the graph paper and are easy to read (e.g., 1, 2, 5 or multiples thereof – avoid 3, 7, 9). Label axes with quantity, symbol and unit. Plot data points with small crosses or encircled dots, and draw a best-fit line or curve.

将自变量绘于 x 轴，因变量绘于 y 轴。选择合适的坐标标度，使其占据图纸一半以上面积并易于读取（如 1、2、5 或其倍数，避免 3、7、9）。轴标签须包含物理量、符号和单位。数据点用细小十字或圆点标出，并画出最佳拟合直线或曲线。

When the relationship is expected to be linear, draw the best-fit straight line with a ruler. For curves, sketch a smooth line. Do not connect dots dot-to-dot unless instructed to.

若预期关系为线性，则用直尺画出最佳拟合直线。对于曲线，勾勒一条光滑曲线，除非另有指示，否则不要逐点连线。

Use the graph to identify anomalous points that deviate from the trend; recalculate or remeasure if possible, and explain why they may have occurred.

利用图表识别偏离趋势的异常点；如有可能则重新计算或重新测量，并解释其产生原因。

7. Gradient and Intercept Analysis | 斜率与截距分析

The gradient of a straight-line graph gives important physical quantities. For example, in a graph of V against I for a resistor, the gradient = R. For a graph of v² against h in free fall, gradient = 2g. Use a large triangle to calculate the gradient, ensuring Δx and Δy are read from your best-fit line, not from data points.

直线图的斜率可给出重要的物理量。例如，在 V–I 图中，斜率 = R。在自由落体实验的 v²–h 图中，斜率 = 2g。使用大三角形计算斜率，并确保 Δx 和 Δy 是从最佳拟合线上读取，而非数据点。

slope = (y₂ – y₁) / (x₂ – x₁)

Calculate the uncertainty in the gradient by drawing worst-fit lines (steepest and shallowest reasonable lines) and using: Δslope = (slope_max – slope_min) / 2.

通过绘制最不拟合线（合理的最大和最小斜率线）计算斜率的不确定度：Δ斜率 = (斜率_max – 斜率_min) / 2。

The y-intercept can also be read from the graph or calculated from the equation of the line, and its physical meaning should be discussed.

y 轴截距可从图中读取或由直线方程计算得出，并讨论其物理意义。

8. Logarithmic Graphs and Exponential Relationships | 对数图与指数关系

Many A2 experiments involve exponential decay (capacitor discharge, radioactive decay) or power laws. For an exponential relationship V = V₀ e⁻ᵗ/ʳᶜ, a graph of ln V against t gives a straight line with gradient = –1/RC. For a power law y = k xⁿ, a graph of log y against log x yields gradient = n.

许多 A2 实验涉及指数衰减（电容器放电、放射性衰变）或幂律关系。对于指数关系 V = V₀ e⁻ᵗ/ʳᶜ，绘制 ln V 对 t 的图可得直线，其斜率 = –1/RC。对于幂律 y = k xⁿ，绘制 log y 对 log x 的图，其斜率 = n。

ln V = ln V₀ – t/RC

log y = n log x + log k

Be able to choose natural logs (ln) or logs to base 10 (log) appropriately and handle units inside logarithms by taking ratios. Usually you plot ln(V/V) or log(x/x₀) to avoid the issue of logs of units.

能够恰当地选择自然对数（ln）或以 10 为底的对数（log），并通过取比值处理对数内的单位。通常绘制 ln(V/V₀) 或 log(x/x₀) 来避免单位取对数的问题。

9. Evaluating Experimental Procedures | 评估实验程序

Evaluations involve discussing limitations, sources of error, and reliability. Consider systematic errors such as a mass balance not zeroed, friction in a pulley, or internal resistance of a voltmeter. Random errors might be caused by fluctuations in temperature, timing inconsistencies, or vibrations.

评估包括讨论局限性、误差来源和可靠性。考虑系统误差，如天平未调零、滑轮存在摩擦、电压表内阻等。随机误差可能由温度波动、计时不一致或振动引起。

For each limitation, propose realistic and specific improvements. Instead of ‘use better equipment’, suggest ‘use a light gate and data logger to remove reaction time error’, or ‘apply a lubricant to reduce friction in the pulley’.

对每个局限性提出切实而具体的改进措施。不要只说“使用更好的设备”，应建议“使用光门和数据记录器以消除反应时间误差”，或“给滑轮加润滑油以减少摩擦”。

You should also comment on whether repeated readings have been taken, whether the range of measurements is adequate, and whether the graph confirms the expected relationship.

还应评论是否进行了重复读数，测量范围是否足够，以及图表是否证实了预期关系。

10. Identifying Key Sources of Error and Improvements | 识别关键误差来源与改进

Be able to prioritise the largest source of uncertainty. For instance, in a pendulum experiment for g, the human reaction time when timing 20 oscillations is likely the dominant uncertainty. Reducing the percentage uncertainty can be achieved by timing more oscillations (e.g., 50) or using a photogate.

能够判断最大的不确定度来源。例如，在用单摆测 g 的实验中，计时 20 个周期时的人为反应时间很可能是主要的不确定度来源。可通过计时更多周期（如 50 个）或使用光电门来降低百分不确定度。

In capacitor discharge experiments, the uncertainty in voltage readings often dominates; use a digital voltmeter with higher resolution and take several sets of readings.

在电容器放电实验中，电压读数的不确定度通常占主导；使用分辨率更高的数字电压表并记录多组数据。

Always connect your improvement directly to the identified error: ‘The random error in measuring diameter with a micrometer could be reduced by taking readings at several orientations and using the mean’, not just ‘repeat measurements’.

始终将改进措施与已识别的误差直接关联：“用千分尺测量直径时的随机误差可通过在多个方向上读数并取平均值来减小”，而不是仅仅说“重复测量”。

11. Key Year 13 WJEC Experiments | WJEC Year 13 核心实验

Expect questions on these practical contexts: determination of g by free fall (using trap door, electromagnet, or light gates), investigation of capacitor charge and discharge (V–t and I–t graphs, time constant RC), Young modulus of a metal wire (using a travelling microscope and weights, stress–strain graph), radioactive decay simulation (dice or protactinium generator, ln N against t), investigation of factors affecting resonant frequency, and investigation of the inverse square law for gamma radiation using a Geiger-Müller tube.

可能考查以下实验情境：自由落体测 g（利用衔铁门、电磁铁或光门），电容器充放电研究（V–t 和 I–t 图，时间常数 RC），金属丝的杨氏模量（用游标显微镜和砝码，应力–应变图），放射性衰变模拟（骰子或镤发生器，ln N–t 图），影响共振频率因素的探究，以及使用盖革-米勒管验证 γ 辐射的平方反比定律。

For each experiment, be able to list the apparatus, describe the step-by-step procedure, state the key variables (independent, dependent, controlled), and explain what graph you would plot and how to extract the sought quantity from its gradient or intercept.

对于每个实验，能够列出仪器、描述分步操作、陈述关键变量（自变量、因变量、控制变量），并解释你会绘制什么图以及如何从斜率或截距中提取待求量。

12. Exam Technique for Practical Questions | 实验题应试技巧

In written papers, practical questions often begin with data in a table and ask you to complete missing values, calculate means, uncertainties, or percentage differences. Show your workings clearly and always quote the uncertainty to 1 significant figure (or 2 if the leading digit is 1) and match the decimal places of the value to those of its uncertainty.

在笔试试卷中，实验题通常先给出数据表格，要求你补全缺失值、计算平均值、不确定度或百分差异。清晰展示计算步骤，不确定度通常保留 1 位有效数字（若首位数字为 1 则保留 2 位），并让数值的小数位与不确定度的小数位保持一致。

When asked to ‘Describe how you would measure…’, give a logical sequence: set up the apparatus, describe how to change the independent variable (with details of ranges and intervals), how to measure the dependent variable (using a specific instrument and reading technique), and how to control other variables. End with ‘repeat and average’.

当被问及“描述你如何测量……”时，要给出逻辑顺序：搭建仪器，描述如何改变自变量（包括范围和间隔细节），如何测量因变量（使用具体仪器和读数技术），以及如何控制其他变量。最后以“重复测量并取平均值”结尾。

For calculation questions, convert all uncertainties to percentage form where multiplication/division occurs. In evaluations, always link your comment to the data: ‘the value calculated for g is within 5% of the accepted value, which is considered accurate’, or ‘the large scatter in points suggests significant random error’.

对于计算题，凡涉及乘除时，将所有不确定度转化为百分形式。在评估部分，始终将评语与数据挂钩：“计算得到的 g 值在公认值的 5% 以内，可认为是准确的”，或“数据点较大的分散表明存在显著的随机误差”。

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Year 13 WJEC Physics: Practical Assessment Key Points | Year 13 WJEC 物理：实验/实践考核要点