📚 Mastering the PH02 Insert for International AS Physics (Jan 2023) | 攻克2023年1月国际AS物理PH02插入页概念
The PH02 Insert provided during the International AS Physics examination in January 2023 serves as a vital reference sheet, containing essential formulas, constants, and circuit symbols for the Waves and Electricity topics. Mastering these concepts not only helps you apply the right equation but deepens your understanding of the underlying physics.
2023年1月国际AS物理考试提供的PH02插入页是一份重要的参考资料，包含了波与电学部分的核心公式、常数和电路符号。掌握这些概念不仅能帮助你正确选用方程，更能加深你对底层物理原理的理解。
1. What the Insert Contains | 插入页包含什么
The insert typically lists key relationships for wave phenomena and electrical circuits. It acts as a memory aid, but simply copying a formula is never enough; you must interpret variables, units, and the physical conditions where each equation holds true.
插入页通常列出了波动和电路的关键关系式。它起到记忆辅助的作用，但仅仅照抄公式远远不够；你必须正确解读变量、单位以及每个方程成立的物理条件。
Familiarise yourself with the layout: wave formulas appear first, followed by electricity equations, and finally standard circuit symbols. Knowing where to look saves precious time in the exam hall.
先熟悉排版：波动公式在最前面，然后是电学方程，最后是标准电路符号。知道去哪里找，能在考场上节省宝贵时间。
2. Wave Fundamentals: v = f λ and T = 1/f | 波的基础：v = f λ 与 T = 1/f
The wave speed equation, v = fλ, links velocity v, frequency f, and wavelength λ. It applies to all progressive waves, provided the medium remains uniform. Always ensure f is in hertz, λ in metres, and v in m s⁻¹.
波速公式 v = fλ 将速度 v、频率 f 与波长 λ 联系起来。它适用于所有行波，前提是介质均匀。务必确保 f 用赫兹，λ 用米，v 用米/秒。
The period T is the reciprocal of frequency: T = 1/f. You often need this when analysing oscilloscope traces or time-base settings. If a wave has a frequency of 50 Hz, its period is 0.02 s.
周期 T 是频率的倒数：T = 1/f。分析示波器轨迹或时基设置时经常用到。若波频率为 50 Hz，其周期为 0.02 s。
3. Refraction and Snell’s Law | 折射与斯涅尔定律
The insert gives Snell’s law in the form n₁ sin θ₁ = n₂ sin θ₂ or simply n = sin i / sin r when light enters from air. Remember that angles are always measured from the normal line. Refractive index n has no units.
插入页给出的斯涅尔定律形式为 n₁ sin θ₁ = n₂ sin θ₂，或当光从空气射入时简化为 n = sin i / sin r。切记角度总是从法线量起。折射率 n 没有单位。
When light travels from a denser medium to a less dense one, total internal reflection can occur. The critical angle C is given by sin C = 1/n. This only applies if the ray is in the optically denser medium and n > 1.
当光从光密介质射向光疏介质时，可能发生全内反射。临界角 C 由 sin C = 1/n 给出。这仅适用于光线在光密介质中且 n > 1 的情况。
4. Diffraction Gratings and Interference | 衍射光栅与干涉
The grating equation d sinθ = nλ is central to interference patterns. Here d is the grating spacing (the reciprocal of lines per metre), θ is the angle of the nth-order maximum, and n is an integer (0, ±1, ±2 …).
光栅方程 d sinθ = nλ 是干涉图样的核心。其中 d 是光栅间距（每米线数的倒数），θ 是第 n 级极大值的角度，n 为整数（0、±1、±2……）。
Use this equation to determine the wavelength of monochromatic light or the grating constant. A finer grating (smaller d) produces more widely spaced maxima. Remember that sinθ cannot exceed 1, which sets an upper limit on the observable orders.
利用该方程可确定单色光的波长或光栅常数。光栅越密（d 越小），极大值间距越大。记住 sinθ 不能超过 1，这限制了可观察级数的上限。
5. Charge, Current and Voltage | 电荷、电流与电压
Electric current is the rate of flow of charge: I = ΔQ / Δt. The unit of charge is the coulomb, and 1 A = 1 C s⁻¹. In a metallic conductor, current is due to the movement of free electrons, but conventional current flows from positive to negative.
电流是电荷流动的速率：I = ΔQ / Δt。电荷单位是库仑，1 A = 1 C s⁻¹。金属导体中电流源于自由电子移动，但约定电流方向是从正到负。
Potential difference (voltage) is defined as work done per unit charge: V = W / Q. One volt equals one joule per coulomb. This definition underpins energy transfers in all circuit components.
电势差（电压）定义为单位电荷所做的功：V = W / Q。一伏特等于一焦耳每库仑。这一定义是所有电路元件能量转移的基础。
6. Resistance and Ohm’s Law | 电阻与欧姆定律
For an ohmic conductor at constant temperature, R = V / I remains constant. The insert lists this as a defining equation, but you must recognise that not all components obey Ohm’s law; a filament lamp or diode does not yield a straight-line I–V graph.
对于恒温下的欧姆导体，R = V / I 保持恒定。插入页将此列为定义式，但你必须认识到并非所有元件都遵守欧姆定律；灯丝灯泡或二极管的 I–V 图并非直线。
The unit of resistance is the ohm (Ω). When interpreting the formula, remember that V is the potential difference across the component and I is the current through it. Misplacing these can lead to errors in circuit analysis.
电阻的单位是欧姆（Ω）。解读公式时，记住 V 是元件两端的电势差，I 是流过它的电流。混淆这些会导致电路分析出错。
7. Resistivity and Geometric Factors | 电阻率与几何因素
Resistance depends on material and shape: R = ρL / A, where ρ is resistivity (Ω m), L is length, and A is cross-sectional area. This formula explains why long, thin wires have higher resistance.
电阻取决于材料与形状：R = ρL / A，其中 ρ 为电阻率（Ω m），L 是长度，A 是横截面积。该公式解释为何长而细的导线电阻更高。
Resistivity is temperature-dependent; for metals it increases with temperature because greater ionic vibrations scatter electrons more. In thermistors, resistivity decreases as temperature rises, which is crucial for sensor applications.
电阻率与温度有关；金属的电阻率随温度升高而增大，因为离子振动更剧烈，散射电子更多。热敏电阻的电阻率则随温度升高而下降，这对传感器应用至关重要。
8. Series and Parallel Combination Rules | 串并联组合规则
| Series | Parallel |
| Rtotal = R₁ + R₂ + … | 1/Rtotal = 1/R₁ + 1/R₂ + … |
| Same current through all components | Same voltage across all branches |
The insert gives the reciprocal formula for parallel resistors. Many students forget to take the final reciprocal after summing 1/R. For two parallel resistors, the shortcut Rtotal = (R₁ × R₂) / (R₁ + R₂) can be derived, but only works for two branches.
插入页给出了并联电阻的倒数公式。很多学生忘记在求和 1/R 之后取倒数。对于两个并联电阻，可推导出速算公式 Rtotal = (R₁ × R₂) / (R₁ + R₂)，但仅适用于两条支路。
9. EMF and Internal Resistance | 电动势与内阻
A real source of emf has internal resistance r, causing terminal voltage to drop when current flows: ε = I(R + r) or V = ε – Ir. The insert may present either form; both express energy conservation per unit charge.
实际的电动势源具有内阻 r，导致有电流时端电压下降：ε = I(R + r) 或 V = ε – Ir。插入页可能给出任一形式；两者都表达了单位电荷的能量守恒。
To find ε and r experimentally, plot V against I. The y-intercept gives ε, and the gradient magnitude gives r. Make sure you know which axis represents voltage and which represents current.
实验确定 ε 和 r 时，绘制 V 随 I 变化的图像。y 轴截距为 ε，斜率大小为 r。务必清楚哪个轴代表电压、哪个轴代表电流。
10. Potential Dividers and Sensors | 分压器与传感器
The potential divider equation is Vout = Vin × (R₂ / (R₁ + R₂)). It appears frequently with sensors: a thermistor or LDR replaces one of the resistors, converting a change in physical quantity into a changing voltage.
分压器公式为 Vout = Vin × (R₂ / (R₁ + R₂))。经常与传感器一同出现：用热敏电阻或光敏电阻替代其中一个电阻，将物理量变化转换为电压变化。
If the variable resistor is R₂ and its resistance increases, Vout rises. Reversing the positions swaps the effect. Understanding this allows you to design circuits for light or temperature sensing.
若可变电阻为 R₂ 且其阻值增大，则 Vout 上升。互换位置则效果反转。理解这点就能设计光感或温感电路。
11. Electrical Power and Energy | 电功率与能量
Three equivalent expressions for power appear in the insert: P = IV, P = I²R, P = V²/R. Use P = IV when both current and voltage are known; use P = I²R for series circuits where current is constant; use P = V²/R for parallel circuits where voltage is constant.
插入页上功率有三个等效表达式：P = IV、P = I²R、P = V²/R。已知电流和电压时用 P = IV；串联电路电流不变时用 P = I²R；并联电路电压不变时用 P = V²/R。
Energy transferred can be found by multiplying power by time: E = Pt. The kilowatt-hour (kW h) is a practical unit of energy: 1 kW h = 3.6 × 10⁶ J. This often appears in questions about domestic electricity costs.
能量转移可由功率乘以时间求得：E = Pt。千瓦时（kW h）是实用的能量单位：1 kW h = 3.6 × 10⁶ J。这常出现在家用电费计算问题中。
12. Effective Use of the Insert in Exams | 在考试中有效使用插入页
Do not waste time searching the insert for a formula you have memorised. Instead, use it to verify units and check unusual forms, such as rearranged resistivity equation. Circle the symbols you intend to use while reading the question.
不要在插入页上浪费时间去寻找你已经记住的公式。相反，用它来核实单位并检查少见的形式，比如变形后的电阻率公式。读题时圈出打算使用的符号。
The circuit symbols on the insert are standard, but ensure you draw them clearly in descriptive answers. A scribbled symbol that looks like a fuse might lose you marks if the examiner mistakes it for a fixed resistor.
插入页上的电路符号都是标准的，但在描述性答案中一定要画清楚。画的潦草的符号如果看起来像熔断器，可能会被考官错认为是固定电阻而失分。
Finally, remember that physics is more than equations—conceptual understanding will guide you when the insert offers multiple relevant formulas, helping you select the one that fits the physical scenario.
最后，记住物理不仅是方程——当插入页提供多个相关公式时，概念理解将引导你选择符合物理情景的那一个。
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