📚 Year 13 WJEC Physics: Key Points for Experimental Practical Assessments | Year 13 WJEC 物理：实验/实践考核要点
The Year 13 practical assessment for WJEC Physics is heavily weighted in Unit 6: Experimental Physics. This unit tests your ability to plan, carry out and evaluate a laboratory investigation (Task A) and to analyse given experimental data in a written paper (Task B). Mastering specific practical skills – from handling uncertainties to linearising equations – is essential for achieving top marks.
WJEC 物理 Year 13 的实验考核重点集中在单元六（实验物理）上。该单元不仅考查你在实验室中计划、实施并评估一个探究实验的能力（任务 A），还要在笔试中分析给出的实验数据（任务 B）。熟练掌握从不确定度处理到方程线性化等专项实践技能，是取得高分的关键。
1. Overview of Unit 6 Experimental Physics | 单元六实验物理概述
Unit 6 is worth 60 raw marks and consists of two components: the Experimental Task (Task A, internally assessed, 30 marks) and the Practical Analysis Task (Task B, externally marked written paper, 30 marks). In Task A you will receive a brief and have to design your own procedure, collect data and evaluate your method. Task B gives you a set of results and requires graph plotting, calculations and critical evaluation.
单元六共 60 分，包含两个部分：实验任务（任务 A，校内考核，30 分）和实验分析任务（任务 B，外加阅卷的笔试，30 分）。在任务 A 中你会得到一个实验纲要，需要自行设计步骤、采集数据并评估方案。任务 B 则提供一组测量结果，要求你进行绘图、计算和批判性评估。
2. Planning and Experimental Design | 实验计划与设计
Begin by stating a clear aim and identifying the independent, dependent and at least three control variables. Explain exactly how you will vary the independent variable (e.g., by adding slotted masses) and measure the dependent variable (e.g., with an oscilloscope or light gate). A step-by-step method is expected.
开始时要清晰陈述实验目的，并识别出独立变量、因变量和至少三个控制变量。准确说明你将如何改变独立变量（例如添加槽码）以及如何测量因变量（例如用示波器或光闸）。务必写出逐步操作步骤。
Include a list of apparatus with ranges and sensitivities. For example, list a digital multimeter set to 20 V DC (±0.01 V), a stopwatch reading to 0.01 s, and a micrometer screw gauge with resolution 0.01 mm. Reference any data-logging equipment and state its sampling rate if relevant.
给出仪器清单并注明量程和精度。例如，列出一台设在 20 V 直流档的数字万用表（±0.01 V）、一块读数到 0.01 s 的秒表，以及一把分辨率为 0.01 mm 的千分尺。若使用数据记录仪，应说明其采样率。
A thorough risk assessment is mandatory. Identify hazards (e.g., heavy masses falling, hot components, ionising radiation from sealed sources) and state clear control measures (use safety screens, wear goggles, limit exposure time).
完善的风险评估必不可少。指出危险源（例如重物坠落、高温元件、密封放射源的电离辐射），并陈述明确的控制措施（使用防护屏、佩戴护目镜、限制照射时间）。
3. Making Accurate Measurements | 进行精确测量
Take repeat readings whenever possible – at least three for each value of the independent variable. Calculate a mean and identify any anomalous results that lie far outside the expected spread. For single measurements (e.g., temperature or length of a fixed wire), state how you minimised parallax error by using a mirror scale or setting the eye perpendicular to the scale.
尽量对每个独立变量值重复测量——至少三次。计算平均值，并识别出明显偏离预期范围的异常结果。对于单次测量（例如温度或固定导线长度），说明你是如何将视差减到最小的，比如使用镜面标尺或将视线垂直于刻度。
Record the instrumental uncertainty as half the smallest scale division for analogue devices and the last digit of the display for digital instruments. For example, an analogue ammeter with 0.1 A divisions gives an absolute uncertainty of ±0.05 A; a digital voltmeter reading 4.32 V has an uncertainty of ±0.01 V.
记录仪器不确定度：模拟仪器取最小分度值的一半，数字仪器取显示的最后一位。例如，最小分度为 0.1 A 的模拟电流表给出的绝对不确定度为 ±0.05 A；读数为 4.32 V 的数字电压表的不确定度为 ±0.01 V。
For derived quantities, time 10–20 oscillations rather than a single one. This reduces the percentage uncertainty in the period by a factor of n, because the absolute timing uncertainty is spread over n cycles.
对于导出量，测量 10–20 次振荡而非单次。这样可将周期的百分不确定度降低至 1/n，因为绝对计时不确定度被均摊到了 n 个周期上。
4. Recording and Presenting Data | 记录与呈现数据
All data must be entered into neat ruled tables. Each column heading should show the quantity, its symbol and the unit with a forward slash, e.g., ‘Current, I / A’, ‘Time for 20 oscillations, 20T / s’. Readings must be consistent in terms of the number of decimal places.
所有数据必须填入标准的划线表格。每一列的标题应标注物理量、符号及用斜线隔开的单位，例如 ‘Current, I / A’、 ‘Time for 20 oscillations, 20T / s’。读数的有效数字或小数位要保持一致。
Significant figures should reflect the precision of the measuring instrument. A typical table might look like:
有效数字需要反映测量仪器的精度。典型的表格如下：
| Mass, m / kg | Weight, W / N | Extension, x / mm |
|---|---|---|
| 0.100 ± 0.001 | 0.98 | 5.2 ± 0.5 |
| 0.200 ± 0.001 | 1.96 | 10.8 ± 0.5 |
5. Graph Plotting Skills | 绘图技能
Use a full page of graph paper for every graph. Label the axes with the quantity and unit, e.g., ‘T² / s²’. Choose scales that are simple (multiples of 1, 2, 5 or 10) and spread the data over at least half of each axis. Do not use awkward scales like 3, 7 or 13.
每次绘图都要使用整张坐标纸。坐标轴标注物理量和单位，例如 ‘T² / s²’。选取简单比例（1、2、5 或 10 的倍数）并使数据点占据每根轴至少一半以上。避免使用 3、7 或 13 这类不便读取的比例。
Plot points with a fine cross (×) or small circle with a dot at the centre. After plotting, draw a best‑fit straight line or a smooth curve – do not connect dot‑to‑dot. Identify any outliers and clearly label them; exclude them from the best‑fit line.
用小叉号（×）或带中心点的小圆圈描点。描点后，画出最佳拟合直线或平滑曲线，不要逐点连接。找出任何异常点并清晰标注；将它们排除在最佳拟合线之外。
If the relationship is expected to be directly proportional, the best‑fit line must pass through the origin only if there is a valid theoretical reason. Otherwise allow a non‑zero intercept.
如果预期关系为正比关系，那么只有具备合理理论依据时才让最佳拟合线通过原点。否则应允许非零截距。
6. Determining Gradients and Intercepts | 确定斜率和截距
To calculate the gradient, draw a large right‑angled triangle on the best‑fit line. Use points that lie on the line (not data points) and read coordinates with maximum precision. State the gradient with its unit, which is the ratio of the y‑axis unit to the x‑axis unit.
为求斜率，在最佳拟合线上画一个大的直角三角形。选取线上的点（非原始数据点）并以最高精度读取坐标。斜率要带单位写出，其单位是纵轴单位与横轴单位之比。
The y‑intercept is read directly from the graph where x = 0. When the relationship is linearised, the gradient and intercept give experimental values of physical constants. For the mass‑spring system, plotting T² against m yields a gradient of 4π²/k. The spring constant is then calculated as:
y 截距可直接从图中 x = 0 处读取。当关系被线性化后，斜率和截距可给出物理常数的实验值。对质量‑弹簧系统，绘制 T² 对 m 的图，斜率是 4π²/k。弹簧劲度系数随之求得：
k = 4π² / gradient
Similarly, for a capacitor discharging through a resistor, the equation V = V₀ e^(−t/RC) is linearised to ln V = ln V₀ − t/RC. A graph of ln V against t yields a straight line with gradient = −1/RC.
同样地，电容通过电阻放电时，V = V₀ e^(−t/RC) 线性化为 ln V = ln V₀ − t/RC。绘制 ln V 对 t 的图得到一条直线，其斜率 = −1/RC。
7. Uncertainty and Error Analysis | 不确定度与误差分析
For repeated readings, the absolute uncertainty can be taken as half the spread: Δx = (x_max − x_min)/2. The percentage uncertainty is then:
对于重复读数，绝对不确定度可取极差的一半：Δx = (x_max − x_min)/2。则百分不确定度为：
% uncertainty = (Δx / x_mean) × 100%
When combining uncertainties, remember these simple rules:
For addition or subtraction (y = a + b or y = a − b): add absolute uncertainties: Δy = Δa + Δb.
For multiplication or division (y = ab or y = a/b): add percentage uncertainties: %U(y) = %U(a) + %U
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