📚 AQA AS Physics Unit 2 Insert (Jan 2020) Explained | AQA AS 物理 Unit 2 附录全解析（2020年1月）
The January 2020 AQA AS Physics Unit 2 paper came with an official insert — the Data and Formula Booklet. This booklet is not just a source of equations; it is a strategic exam tool. Students who know exactly what is on the insert save working memory, avoid transcription errors, and solve numerical questions faster. This revision guide breaks down every key formula and constant on the Jan 2020 insert, explains when to use each one, and highlights common traps.
2020年1月AQA AS物理Unit 2试卷附带官方附录——数据与公式手册。这份附录不只是公式来源，更是考场上的战略工具。熟悉附录内容的学生能节省工作记忆、避免抄写错误，并更快地解答计算题。本复习指南逐一拆解Jan 2020附录中的关键公式和常数，说明使用时机，并指出常见陷阱。
1. Inside the Insert | 附录的结构
The insert has two clear parts: a table of physical constants and a list of equations grouped by topic — mechanics, materials, waves and electricity. The layout is identical every year for AQA AS Physics, so once you learn where each equation sits, you can flick to it instantly in the exam.
附录由两大部分组成：物理常数表和按主题分组的公式表——力学、材料、波动和电学。AQA AS物理每年的附录布局完全一致，因此一旦你记住每条公式的位置，考试时就能迅速定位。
The most frequently needed constants from the Jan 2020 insert are listed below.
下面列出Jan 2020附录中最常使用的常数。
| Quantity 物理量 | Symbol 符号 | Value 数值 |
| speed of light in vacuum 真空光速 | c | 3.00 × 10⁸ m s⁻¹ |
| Planck constant 普朗克常数 | h | 6.63 × 10⁻³⁴ J s |
| elementary charge 元电荷 | e | 1.60 × 10⁻¹⁹ C |
| electron rest mass 电子静质量 | mₑ | 9.11 × 10⁻³¹ kg |
| proton rest mass 质子静质量 | mₚ | 1.67 × 10⁻²⁷ kg |
| gravitational field strength 重力场强度 | g | 9.81 N kg⁻¹ |
2. Kinematics Equations | 运动学公式
The insert gives four uniform-acceleration equations. They are valid only when acceleration is constant. Choose an equation by listing what you know and what you need.
附录给出四条匀加速运动方程。它们仅在加速度恒定时成立。解题时应先列出已知量和待求量，再选择对应方程。
v = u + at
s = ut + ½at²
v² = u² + 2as
s = ½(u + v)t
Always check the direction sign: with up as positive, g = −9.81 m s⁻² for a rising object.
例如，若Jan 2020题中给出初速度、加速度和时间而未给末速度，直接用第一条方程。若需求位移但没有时间，则用v² = u² + 2as。务必注意方向符号：取向上为正时，上升物体的g = −9.81 m s⁻²。
3. Forces and Newton's Laws | 力与牛顿定律
Newton' y W = mg. The insert also lists moment = Fd, which often appears in equilibrium questions.
附录中牛顿第二定律写作F = ma，重力由W = mg给出。附录还列出力矩表达式moment = Fd，常见于平衡问题。
F = ma W = mg moment = Fd
f several forces act, find the resultant first and then apply F = ma to find acceleration.
在Jan 2020风格的题目中，你可能需要分解力。附录不提供三角恒等式，因此必须牢记sin θ和cos θ关系。若多个力作用，先求合力，再代入F = ma求加速度。
4. Momentum and Impulse | 动量与冲量
Momentum is listed as p = mv, and impulse as Ft = mv − mu. The impulse–momentum form is essential for collision and explosion questions.
附录中动量写作p = mv，冲量写作Ft = mv − mu。冲量–动量形式对碰撞和爆炸类问题至关重要。
p = mv Ft = mv − mu
Momentum is conserved in a closed system. In a Jan 2020 collision question, write the total momentum before and after as equal, substitute the given masses and velocities, then solve for the unknown. Remember that velocity has direction, so one object moving in the negative direction carries a negative sign.
在封闭系统中动量守恒。解Jan 2020碰撞题时，写出碰撞前后总动量相等，代入已知质量和速度，再解未知量。注意速度具有方向性，朝负方向运动的物体应取负号。
5. Work, Energy and Power | 功、能量与功率
Eₚ = mgh. Power is defined as work per unit time, P = W/t, and for constant force, P = Fv.
附录给出功W = Fs、动能Eₖ = ½mv²、重力势能Eₚ = mgh。功率定义为单位时间做功P = W/t，对恒力情形有P = Fv。
W = Fs Eₖ = ½mv² Eₚ = mgh P = W/t = Fv
Energy conservation questions appear every year. For a falling object, equate the loss of gravitational potential energy to the gain in kinetic energy before solving for speed. If resistive forces are present, subtract the work done against resistance from the total energy change.
能量守恒问题每年必考。对下落物体，令重力势能减少量等于动能增加量，再求速度。若存在阻力，应从总能量变化中扣掉克服阻力所做的功。
6. Materials: Stress, Strain and Young Modulus | 材料：应力、应变与杨氏模量
The insert provides the definitions of stress and strain, together with the Young modulus formula. These appear in Unit 2 materials questions.
附录给出应力和应变的定义，以及杨氏模量公式。这些出现在Unit 2材料类问题中。
stress = F/A strain = ΔL/L E = stress / strain
Stress has units of N m⁻² (Pa) and strain is dimensionless because it is a ratio of two lengths. A Jan 2020 question might provide force, cross-sectional area and extension, and ask for the Young modulus. Convert all lengths to metres before substitution.
应力单位为N m⁻²（Pa），应变为无量纲量，因为它是两个长度的比值。Jan 2020题可能给出力、横截面积和伸长量，要求计算杨氏模量。代入前务必将所有长度换算为米。
tential energy. The insert also gives elastic potential energy as ½FΔL or ½kΔL² from Hooke's law F = kΔL.
不要将杨氏模量与弹性势能混淆。附录还给出弹性势能½FΔL或½kΔL²，来源是胡克定律F = kΔL。
7. Waves: Speed, Frequency, Wavelength | 波动：波速、频率与波长
t is v = fλ. It links wave speed, frequency and wavelength, and applies to all wave types.
附录中的核心波动方程是v = fλ。它将波速、频率和波长联系起来，适用于所有波类型。
v = fλ
ve using λ = c/f. Check the unit of frequency: if it is given in MHz, convert to Hz first.
对电磁波而言，波速v即光速c，附录给出c = 3.00 × 10⁸ m s⁻¹。Jan 2020常见题型是用λ = c/f计算光波波长。注意频率单位：若以MHz给出，先换算为Hz。
8. Refraction and Optics | 折射与光学
The insert includes the refractive index formula. When light passes from one medium to another, the ratio of the sines of the angles is constant.
附录包含折射率公式。当光从一种介质进入另一种介质时，入射角与折射角的正弦之比为常数。
n = sin i / sin r
n = c/v
For a Jan 2020 refraction question, identify which angle is in air/vacuum and which is in the glass. Remember that when light speeds up (moving into a rarer medium), the ray bends away from the normal. If the calculated sin r would exceed 1, total internal reflection occurs.
解Jan 2020折射题时，先判断哪个角在空气/真空中，哪个角在玻璃中。记住光进入更疏介质时速度增大，光线远离法线。若计算出的sin r大于1，则发生全反射。
9. Electricity: Charge, Voltage, Resistance | 电学：电荷、电压与电阻
uit questions: charge flow ΔQ = IΔt, potential difference V = W/Q, and resistance R = V/I.
附录给出贯穿所有电路题的基本定义：电荷量ΔQ = IΔt、电势差V = W/Q、电阻R = V/I。
ΔQ = IΔt V = W/Q R = V/I
These three equations are the starting point for most numerical work. In a Jan 2020 circuit question, you may be given a current and time and asked for the charge, or given the charge and energy and asked for the voltage. Always use SI units: amperes for current, coulombs for charge, seconds for time.
这三条方程是多数计算题的出发点。Jan 2020电路题可能给出电流和时间求电荷量，或给出电荷量和能量求电压。务必使用SI单位：电流用安培、电荷量用库仑、时间用秒。
10. Resistors in Series and Parallel | 电阻的串联与并联
Combining resistors is a core Unit 2 skill. The insert gives both rules clearly.
电阻组合是Unit 2的核心技能。附录清楚给出两组规则。
R = R₁ + R₂ + …
1/R = 1/R₁ + 1/R₂ + …
step by step, calculating the total resistance before applying V = IR to find the current.
串联电路中电阻直接相加，且通过每个电阻的电流相同。并联电路的总电阻小于其中最小电阻。Jan 2020经典题型是串并联混合：逐步化简电路，先求总电阻，再用V = IR求总电流。
11. Power, Resistivity and EMF | 功率、电阻率与电动势
trical power P = VI = I²R = V²/R, resistivity ρ = RA/L, and the EMF relation E = I(R + r).
有三条公式需要仔细理解：电功率P = VI = I²R = V²/R、电阻率ρ = RA/L、电动势关系E = I(R + r)。
