AS AQA Physics Example Responses for PH02 Unit 2: Waves and Electricity | AS AQA 物理 PH02 第二单元示例答题

📚 AS AQA Physics Example Responses for PH02 Unit 2: Waves and Electricity | AS AQA 物理 PH02 第二单元示例答题

Welcome to this exam-focused guide for AQA International AS Physics Unit 2 (PH02). This unit covers waves and electricity, two areas where clear definitions and structured explanations can earn full marks. In this article, we will look at typical exam questions and model responses, explaining how to gain each mark and avoid common errors.

欢迎阅读本期针对 AQA 国际 AS 物理第二单元（PH02）的考试答题指南。本单元涵盖波动与电学，这两部分中清晰的定义和结构化的解释能帮助你获得满分。在本文中，我们将分析典型考题与示例作答，逐一说明如何得分并避免常见错误。

1. Understanding Command Words | 理解指令词

In PH02, the command word tells you exactly what the examiner expects. For example, “define” requires a formal scientific statement, “state” needs a brief factual answer, “calculate” requires working and a final answer with units, and “explain” needs a reason or mechanism. Writing too much may waste time, while writing too little can lose marks.

在 PH02 中，指令词告诉您考官到底期望什么。例如，“define（定义）”需要正式的科学陈述；“state（陈述）”只需简短事实性回答；“calculate（计算）”需要计算过程和带单位的最终答案；“explain（解释）”则需要原因或机制。写得过多会浪费时间，写得太少则会丢分。

Command word	English expectation	Chinese expectation
Define	Give a precise scientific meaning	给出准确的科学含义
State	Give a short factual answer without explanation	给出简短事实性答案，不必解释
Calculate	Show working and give answer with units	展示过程并给出带单位的答案
Explain	Give a reason or account of a process	给出原因或解释过程
Describe	Recall facts or details without explaining	回忆事实或细节，不要求解释
Show	Derive or demonstrate a result	推导或论证某个结果

2. Definition Responses That Score Full Marks | 能拿满分的定义题作答

Exam question: “Define the wavelength of a wave.” (2 marks)

Model answer: “Wavelength is the distance between two adjacent points in phase on a wave, measured along the direction of propagation.”

模型答案：“波长是沿波的传播方向上，两个相邻的同相点之间的距离。”

This definition gains both marks because it includes the key ideas of “adjacent points in phase” and “measured in the direction of propagation”. A common mistake is to say “distance between two peaks” – this may gain only 1 mark because it does not cover all types of waves, such as longitudinal waves where peaks are not relevant.

这个定义能拿两分，因为它包含了“相邻同相点”和“沿传播方向测量”这两个关键概念。一个常见错误是写成“两个波峰之间的距离”，这可能只能得 1 分，因为该表述不适用于纵波等所有波型。

3. Wave Properties: Frequency and Period | 波的特性：频率与周期

Exam question: “State what is meant by the frequency of a wave.” (2 marks)

Model answer: “Frequency is the number of complete oscillations (or wave cycles) passing a fixed point per unit time. It is measured in hertz (Hz).”

模型答案：“频率是单位时间内通过固定点的完整振动（或波周期）的个数，单位是赫兹（Hz）。”

Frequency and period are linked by the equation f = 1/T, where T is the time for one complete oscillation. When answering, always use the word “complete” or “per unit time” to show you understand the definition fully.

频率与周期的关系为 f = 1/T，其中 T 是一次完整振动所需的时间。作答时务必使用“完整”或“单位时间”等词，以表明你完全理解了定义。

f = 1/T

4. The Wave Equation: v = fλ | 波速方程：v = fλ

Exam question: “A wave travels at 3.0 × 10⁸ m s⁻¹ and has a wavelength of 500 nm. Calculate its frequency.” (3 marks)

Model answer:

Step 1: Convert wavelength to metres: λ = 500 nm = 500 × 10⁻⁹ m = 5.00 × 10⁻⁷ m.

第 1 步：将波长转换为米：λ = 500 nm = 500 × 10⁻⁹ m = 5.00 × 10⁻⁷ m。

Step 2: Use v = fλ, so f = v/λ = (3.0 × 10⁸ m s⁻¹) / (5.00 × 10⁻⁷ m) = 6.0 × 10¹⁴ Hz.

第 2 步：利用 v = fλ，得 f = v/λ = (3.0 × 10⁸ m s⁻¹) / (5.00 × 10⁻⁷ m) = 6.0 × 10¹⁴ Hz。

v = fλ

Notice that all quantities are converted to SI units before substitution, and the final answer has a unit (Hz). In calculations, you should show at least one line of substitution and then the final answer to gain method marks even if a numerical slip occurs.

请注意，在代入公式前所有量都转换成了国际单位制，并且最终答案带有单位（Hz）。在计算题中，即使出现数值失误，也应写出至少一步代入过程和最终答案，以便获得方法分。

5. Superposition and Interference | 叠加与干涉

Exam question: “Explain what is meant by constructive interference.” (3 marks)

Model answer: “Constructive interference occurs when two waves meet in phase. Their displacements add together, resulting in a wave of larger amplitude – the sum of the individual amplitudes. This produces a point of maximum intensity.”

模型答案：“当两列波同相相遇时发生相长干涉。它们的位移相互叠加，导致振幅增大——为两者振幅之和，从而产生强度最大的点。”

To score full marks, you must mention “in phase”, “displacements add”, and “larger amplitude” or “maximum intensity”. If asked about destructive interference, say “in antiphase”, “displacements cancel”, and “smaller or zero amplitude”.

要得满分，必须提到“同相”“位移叠加”和“更大振幅”或“最大强度”。如果题目问相消干涉，则需要说“反相”“位移抵消”和“更小或零振幅”。

6. Describing Stationary Waves | 描述驻波

Exam question: “A stationary wave is formed on a string fixed at both ends. Describe the positions of nodes and antinodes.” (3 marks)

Model answer: “Nodes are points of no displacement where the string does not move; they occur at the fixed ends and at intervals of half a wavelength along the string. Antinodes are points of maximum displacement, located halfway between adjacent nodes.”

模型答案：“节点是位移为零、弦不动的位置；它们出现在固定端以及沿弦每隔半个波长的位置。腹点是位移最大的位置，位于相邻节点中间。”

Use the terms “nodes” and “antinodes” correctly and state the half-wavelength spacing. This shows you can recall the structure of a stationary wave, a common question in PH02.

要正确使用“节点”和“腹点”这两个术语，并指出半波长的间距。这表明你能回忆驻波的结构，这是 PH02 中常见的考点。

7. Electrical Quantities: Current and Potential Difference | 电学量：电流与电势差

Exam question: “Define electric current.” (2 marks)

Model answer: “Electric current is the rate of flow of electric charge through a conductor, measured in amperes (A).”

模型答案：“电流是通过导体的电荷流动速率，单位为安培（A）。”

Similarly, you may be asked to define potential difference: “The energy transferred per unit charge from electrical energy to other forms.” Note the formula I = ΔQ/Δt is also useful in calculation questions.

类似地，你可能会被要求定义电势差：“从电能转化为其他形式的能量中，每单位电荷所转移的能量。”记住公式 I = ΔQ/Δt 在计算题中也很有用。

I = ΔQ/Δt

8. I–V Characteristics: Ohmic Conductors | I–V 特性：欧姆导体

Exam question: “State and explain the I–V characteristic for an ohmic conductor at constant temperature.” (4 marks)

Model answer: “The I–V characteristic is a straight line through the origin, showing that the current is directly proportional to the potential difference. This is because the resistance remains constant, so V/I is the same at every point.”

模型答案：“I–V 特性曲线是一条通过原点的直线，表明电流与电势差成正比。这是因为电阻保持恒定，所以任意一点的 V/I 都相同。”

For a filament lamp, you would say that the curve flattens because the resistance increases as temperature rises. Always mention “constant temperature” when quoting Ohm’s law or describing an ohmic conductor.

对于白炽灯，你需要说曲线变平是因为温度升高导致电阻增大。在引用欧姆定律或描述欧姆导体时，务必指出“恒定温度”。

9. Series and Parallel Circuits | 串联与并联电路

Exam question: “A 6 Ω resistor and a 12 Ω resistor are connected (a) in series and (b) in parallel. Calculate the total resistance in each case.” (4 marks)

Model answer:

(a) Series: R_total = R₁ + R₂ = 6 + 12 = 18 Ω.

（a）串联：R_total = R₁ + R₂ = 6 + 12 = 18 Ω。

(b) Parallel: 1/R_total = 1/R₁ + 1/R₂ = 1/6 + 1/12 = 3/12 = 1/4, so R_total = 4 Ω.

（b）并联：1/R_total = 1/R₁ + 1/R₂ =

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AS AQA Physics Example Responses for PH02 Unit 2: Waves and Electricity | AS AQA 物理 PH02 第二单元 示例答题