A-Level Physics: Experimental Design and Planning Essentials | A-Level 物理：实验方案设计与规划要点

📚 A-Level Physics: Experimental Design and Planning Essentials | A-Level 物理：实验方案设计与规划要点

In A-Level Physics, experimental design is a core assessment objective. A well-planned experiment begins with a clear question and ends with a reliable conclusion. This article outlines the essential steps for planning a controlled, accurate and safe physics investigation.

在 A-Level 物理中，实验设计是核心考核目标之一。一项规划良好的实验始于清晰的问题，终于可靠的结论。本文概述了规划一个受控、准确且安全的物理探究所需的关键步骤。

1. Identifying the Aim and Research Question | 确定实验目的与研究问题

Before any apparatus is selected, you must state the aim precisely. For example, “To investigate how the period of a simple pendulum depends on its length.” This turns a vague idea into a testable research question.

在选择任何器材之前，你必须准确表述实验目的。例如：“研究单摆周期如何随摆长变化。”这能将模糊的想法转变为可检验的研究问题。

A good aim should specify the physical quantities involved and the range over which they will be changed. It should also imply the relationship you expect to find, such as a proportional or inverse-square relationship.

一个好的实验目的应指明涉及的物理量以及改变它们的范围，还应暗示你预期发现的关系，例如正比或平方反比关系。

Common mistakes include writing an aim that is too broad, such as “to study pendulums”, or failing to state whether a constant is being measured or a law is being verified. Always make the aim specific enough for another student to repeat.

常见错误包括将目的写得太宽泛，例如“研究单摆”，或没有说明是在测量某个常量还是验证某条定律。务必使目的足够明确，使其他学生可以复现。

2. Identifying Variables | 识别变量

In every experiment, distinguish between the independent variable, the dependent variable and the controlled variables. The independent variable is the one you change; the dependent variable is the one you measure; the controlled variables must be kept constant.

在每个实验中，要区分自变量、因变量和控制变量。自变量是你改变的变量；因变量是你测量的变量；控制变量则必须保持恒定。

Define each variable operationally. For a pendulum, the independent variable is the length l from the pivot to the centre of the bob. The dependent variable is the period T, defined as the time for one complete oscillation. Controlled variables include amplitude, bob mass and air density.

要为每个变量给出操作性定义。对于单摆，自变量是从悬点到摆球中心的长度 l。因变量是周期 T，定义为一次全振动所需的时间。控制变量包括振幅、摆球质量和空气密度。

• Independent variable: e.g. pendulum length l, measured from the pivot to the centre of the bob.

  自变量：例如摆长 l，从悬点到摆球中心的距离。

• Dependent variable: e.g. period T, measured with a stopwatch or light gate.

  因变量：例如周期 T，用秒表或光电门测量。

• Controlled variables: e.g. amplitude, bob mass, air density, release angle.

  控制变量：例如振幅、摆球质量、空气密度、释放角度。

Do not forget to record how each controlled variable is maintained. For example, the amplitude should be kept below 10° by releasing the bob from the same small angle each time.

不要忘记记录每个控制变量如何被维持。例如，应通过每次从相同小角度释放摆球，使振幅保持在 10° 以下。

3. Formulating the Physical Model | 建立物理模型

Based on theory, write down the expected equation. For a simple pendulum, the theoretical period is T = 2π√(l/g). This model tells you which quantities to plot to obtain a straight-line graph.

根据理论，写出预期方程。对于单摆，理论周期为 T = 2π√(l/g)。该模型告诉你应绘制哪些量才能得到直线图。

T = 2π√(l/g)

Squaring both sides gives T² = (4π²/g) l, so a graph of T² against l should be a straight line through the origin with slope 4π²/g. This also allows g to be determined from the slope.

两边平方得到 T² = (4π²/g) l，因此 T² 对 l 的图应为一条过原点的直线，斜率为 4π²/g。这样还可以通过斜率求出 g。

When the model is not linear, choose suitable transformations. For example, if y = axⁿ, plotting log y against log x gives a straight line of slope n. This is a powerful method for identifying unknown power laws

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