📚 Mastering Experimental Investigations: A-Level Physics Unit 5 June 2022 | 精通实验探究：A-Level 物理 Unit 5 2022年6月真题解析
Experimental investigations form the backbone of A-Level Physics Unit 5, testing your ability to design, execute, and evaluate practical work. The June 2022 paper challenges students to think like real scientists – not just recalling facts, but applying the scientific method to unfamiliar scenarios. In this article, we break down the key skills needed to tackle any experimental question, using examples inspired by the Unit 5 Jun22 exam to sharpen your technique and boost your confidence.
实验探究是 A-Level 物理 Unit 5 的核心，考查你设计、实施和评价实践工作的能力。2022 年 6 月的试卷要求学生像真正的科学家一样思考——不仅仅是回忆事实，而是将科学方法应用于不熟悉的场景。本文将分解解决任何实验问题所需的关键技能，并使用受 Unit 5 2022年6月真题启发的示例来提升你的技巧和信心。
1. Understanding the Experimental Context | 理解实验背景
Every Unit 5 practical question begins with a context – often drawn from nuclear, thermal, or astrophysics topics. The Jun22 paper featured investigations such as determining the half-life of a radioactive source, studying gas laws, or analysing capacitor discharge. Quickly identify which physical relationship is being explored and what quantities must be measured.
每道 Unit 5 实验题都以一个背景开始——通常来自核物理、热物理或天体物理主题。2022年6月的试卷涵盖了诸如测定放射源的半衰期、研究气体定律或分析电容器放电等探究。快速识别出要探索的物理关系以及必须测量哪些量。
- ecognise the underlying equation: e.g., N = N₀e⁻λᵗ for decay, or pV = nRT for ideal gases.
- 识别基础方程：例如，衰变中的 N = N₀e⁻λᵗ，或理想气体的 pV = nRT。
- Note any output variables (count rate, volume, current) and input variables (time, temperature, voltage).
- 注意输出变量（计数率、体积、电流）和输入变量（时间、温度、电压）。
2. Identifying Variables and Controls | 识别变量与控制
Examiners expect you to clearly distinguish independent, dependent, and control variables. For a Jun22-style investigation on the inverse square law for gamma radiation, the independent variable is the distance d between source and detector; the dependent variable is the count rate C; control variables could include the source activity, background radiation, and detector orientation.
考官期望你清楚区分自变量、因变量和控制变量。对于 2022年6月风格的反平方律 γ 辐射探究，自变量是源与探测器间的距离 d；因变量是计数率 C；控制变量可能包括源活度、背景辐射和探测器方位。
| Variable Type | Example (Inverse Square Law) |
| Independent | Distance d from source |
| Dependent | Count rate C |
| Control | Background count, source strength |
3. Planning and Apparatus | 实验设计与器材
A robust plan includes a labelled diagram, step-by-step procedure, and justified choice of instruments. In the Jun22 question on specific heat capacity of a metal block, you would need an immersion heater, thermometer, stopwatch, ammeter, voltmeter, and insulation. Explain why a digital thermometer offers better resolution (0.1 °C) than a mercury-in-glass thermometer.
一个可靠的计划包括带标注的示意图、逐步操作步骤以及合理的仪器选择。在 2022年6月关于金属块比热容的题目中，你需要一个浸没式加热器、温度计、秒表、电流表、电压表和绝缘材料。解释为什么数字温度计比水银温度计提供更好的分辨率（0.1 °C）。
Electrical energy supplied = V × I × t → m × c × Δθ
提供的电能 = V × I × t → m × c × Δθ
Use the above energy balance to derive the specific heat capacity c. Ensure you describe repeating measurements and calculating mean values to reduce random errors.
使用上述能量平衡推导比热容 c。确保描述重复测量并计算平均值以减少随机误差。
4. Data Collection Techniques | 数据收集技巧
Precision in data gathering is vital. For the Jun22 radioactive decay experiment, you would use a GM tube connected to a scaler or data logger. Record the count for a fixed time interval (e.g., 10 s) at regular total elapsed times. Always subtract background radiation and note that the GM tube only detects a fraction of emitted particles.
精确的数据收集至关重要。对于 2022年6月的放射性衰变实验，你将使用连接到计数器或数据记录器的盖革管。在固定的时间间隔（例如 10 秒）内，按规律的总经过时间记录计数。始终减去背景辐射，并注意盖革管只能探测到发射粒子的部分。
- Use a large number of counts to minimise statistical uncertainty (√N).
- 使用大量计数以最小化统计不确定度（√N）。
- For gas law investigations, read the volume at eye level to avoid parallax error.
- 对于气体定律探究，在与视线水平的位置读取体积以避免视差误差。
5. Handling Uncertainties | 处理不确定度
. The percentage uncertainty in a quantity = (absolute uncertainty / measured value) × 100% ision, add percentage uncertainties; for addition/subtraction, add absolute uncertainties.
A Level Unit 5 考试题目大量评估不确定度计算。一个量的百分不确定度 =（绝对不确定度 / 测量值）× 100%。组合不确定度时，规则取决于运算：乘除时，相加百分不确定度；加减时，相加绝对不确定度。
λ = ln 2 / T₁/₂, the percentage uncertainty in λ is the same as that in T₁/₂: (2/120)×100% ≈ 1.7%.
2022年6月的试卷可能要求你从测得的半衰期 T₁/₂ 计算衰变常数 λ 的不确定度。如果 T₁/₂ = 120 ± 2 s，λ = ln 2 / T₁/₂，则 λ 的百分不确定度与 T₁/₂ 相同：(2/120)×100% ≈ 1.7%。
6. Graphical Analysis | 图形分析
, a graph of p against 1/V yields a straight line through the origin, with gradient = nRT.
图形将原始数据转化为有意义的物理量。将自变量绘制在 x 轴上。在 2022年6月探究恒温下气体压强与体积关系的背景下，绘制 p 对 1/V 的图会得到一条通过原点的直线，斜率 = nRT。
Remember to use appropriate scales, label axes with quantities and units, and draw a best-fit line (not dot-to-dot). Judge outliers and only exclude them with justification.
记住使用适当的刻度，用物理量和单位标注坐标轴，并绘制最佳拟合线（而非逐点连接）。判断异常值，只在有正当理由时才将其排除。
7. Linearization and Trendlines | 线性化与趋势线
the radioactive decay equation N = N₀e⁻λᵗ, taking the natural logarithm gives ln N = ln N₀ – λt. A graph of ln N against t produces a straight line with gradient –λ.
许多实际关系是非线性的，但 A-Level 物理依靠线性化来提取信息。对于放射性衰变方程 N = N₀e⁻λᵗ，取自然对数得到 ln N = ln N₀ – λt。以 ln N 对 t 作图会产生一条直线，斜率为 –λ。
The Jun22 exam may require you to explain why this manipulation is necessary – it allows better assessment of the relationship and makes uncertainty analysis on the slope straightforward.
2022年6月的考试可能要求你解释为何这种处理是必要的——它可以更好地评估关系，并使对斜率的不确定度分析变得直接。
8. Evaluation of Results | 结果评价
tance, if the accepted value of half-life is 132 s and you obtain 138 ± 3 s, calculate the % difference = |132–138|/132 × 100% ≈ 4.5%. Discuss whether this falls within the experimental uncertainty.
Unit 5 评估的一项关键技能是批判性地反思数据的能力。使用百分差异将你的实验值与公认值进行比较。例如，如果公认的半衰期是 132 秒，而你得到 138 ± 3 秒，计算 % 差异 = |132–138|/132 × 100% ≈ 4.5%。讨论这是否落在实验不确定度范围内。
- If the accepted value lies outside your uncertainty interval, systematic errors are likely present.
- 如果公认值落在你的不确定度区间外，则可能存在系统误差。
- Judge the reliability by comment on the spread of repeated readings.
- 通过评述重复读数的离散程度来判断可靠性。
9. Sources of Error and Improvements | 误差来源与改进
Identifying and suggesting improvements is a common Jun22 question format. For a thermal experiment, heat losses to the surroundings are a major systematic error – improving with better insulation, a lid, or using a joulemeter instead of electrical heater to precisely measure energy input may help.
识别并提出改进是 2022年6月常见的题型格式。对于热学实验，向周围环境的热损失是一个主要的系统误差——通过更好的隔热、使用盖子或使用焦耳计代替电加热器精确测量能量输入可能有助于改进。
For a capacitor discharge experiment, the internal resistance of the voltmeter could affect readings; use a high-impedance digital voltmeter to minimise current drawn.
对于电容器放电实验，电压表的内阻可能影响读数；使用高阻抗数字电压表以最小化汲取的电流。
| Error Source | Improvement |
| Background radiation | Take background count before experiment, subtract, shield surroundings |
| Thermometer response time | Wait for steady reading; use digital sensor with fast response |
10. Sample Question Analysis (Unit 5 Jun22) | 真题示例分析 (Unit 5 2022年6月)
Consider a typical question from the Jun22 paper: 'An experiment is carried out to determine the decay constant of a radioactive isotope. The count rate from a sample is recorded every 30 s. Describe how you would use the data to find the decay constant and estimate its uncertainty.'
考虑 2022年6月试卷中的一道典型题目：“进行了一项实验以测定放射性同位素的衰变常数。每 30 秒记录样品的计数率。描述你将如何使用数据求出衰变常数并估计其不确定度。”
You would:
- Subtract background count rate from all readings.
- 减去所有读数中的背景计数率。
- Plot a graph of ln(corrected count rate) against time. Draw line of best fit.
- 绘制 ln（修正后的计数率）对时间的图。绘制最佳拟合线。
- Determine the gradient m of the line (m = –λ).
- 确定直线的斜率 m（m = –λ）。
- Draw worst-acceptable gradient lines to find Δm; uncertainty in λ = |m – mmin|.
- 绘制最差可接受的梯度线求 Δm；λ 的不确定度 = |m – mmin|。
- State λ with absolute uncertainty and compare to accepted value if given.
- 陈述带有绝对不确定度的 λ，若给定则与公认值比较。
This structured approach directly addresses the mark scheme and demonstrates full practical competence.
这种结构化的方法直接呼应了评分方案，并展示了完整的实践能力。
Published by TutorHao | Physics Revision Series | aleveler.com
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