Unit 3: Practical Skills in Scientific Investigation | 第3单元：科学探究实践技能

📚 Unit 3: Practical Skills in Scientific Investigation | 第3单元：科学探究实践技能

This unit focuses on the practical skills that underpin A-Level science assessment. Whether you are studying physics, chemistry, or biology, Unit 3-style questions test your ability to plan investigations, handle data, evaluate methods, and draw valid conclusions. This revision guide covers the core competencies of scientific investigation through clear stages and examples.

本单元聚焦于 A-Level 科学测评中的实验技能。无论你学习物理、化学还是生物，第3单元型题目都考查你设计研究、处理数据、评价方法和得出有效结论的能力。本复习指南通过清晰的阶段和示例，覆盖科学探究的核心能力。

1. Planning an Investigation | 制定实验计划

A good plan starts with a testable hypothesis and a clear research question. Identify the independent variable (IV), dependent variable (DV), and control variables before choosing apparatus. Include a preliminary trial, a suitable range of readings, and repeated measurements to reduce random error.

好的计划始于可检验的假设和明确的研究问题。在选择仪器之前，先确定自变量（IV）、因变量（DV）和控制变量。计划中应包括预实验、合适的读数范围以及重复测量，以减少随机误差。

A useful planning sequence is: identify variables, select a method, list equipment, choose a range with at least five or six intervals, decide on repeats, and note safety precautions. This structure is exactly what examiners look for in extended practical planning questions.

一个实用的计划顺序是：确定变量、选择方法、列出设备、选择至少五到六个间隔的读数范围、决定重复次数，并记录安全注意事项。这种结构正是考官在扩展实验设计题中所寻找的。

2. Variables and Control | 变量与控制

The independent variable is deliberately changed, the dependent variable is measured, and control variables are kept constant. In A-Level experiments, a common error is failing to identify whether a variable is continuous, discrete, or categoric.

自变量是被刻意改变的变量，因变量是被测量的变量，控制变量则保持不变。在 A-Level 实验中，一个常见错误是未能辨别一个变量是连续型、离散型还是类别型。

Control variables need to be monitored, not just named. For example, if temperature affects the rate, a water bath and thermometer should be used. State the accepted value or the accepted range for each controlled variable, and explain how it was kept constant.

控制变量需要被监控，而不只是被命名。例如，如果温度影响速率，就应使用水浴和温度计。对每个控制变量都应说明可接受的值或可接受的范围，并解释它是如何保持不变的。

3. Common Apparatus and Measurement | 常用仪器与测量

Know the precision of common instruments: a metre rule has a resolution of 1 mm, a micrometer screw gauge has a resolution of 0.01 mm, a digital voltmeter may display 0.01 V, and a stopwatch measures to 0.01 s but human reaction time is about 0.2 s.

要了解常用仪器的分辨率：米尺的分辨率为1毫米，千分尺的分辨率为0.01毫米，数字电压表可能显示0.01伏，秒表可测到0.01秒，但人的反应时间约为0.2秒。