📚 Year 13 Cambridge Physics: A Quick Guide to Key Terms | Year 13 Cambridge 物理：词汇术语速记指南
Mastering A2 Physics requires not just solving equations but internalising the precise terminology that examiners expect. This guide walks you through the essential definitions and key terms for Year 13 Cambridge Physics (9702 syllabus), pairing each term with its Chinese equivalent and a concise explanation. Use it as a fast reference, a self‑test, or a revision companion to sharpen your understanding and boost your confidence before the final papers.
攻克 A2 物理不仅需要熟练解题，更需要把考官期待的精准术语内化于心。这份指南带你梳理 Year 13 Cambridge 物理（9702 大纲）的核心定义与关键词汇，每个术语都配有中文对应词和简明解释。你可以把它当作快速查阅手册、自测工具或复习伴侣，在最后模考和正式考试前加深理解、增强信心。
1. Circular Motion | 圆周运动
Angular displacement (θ) is the angle swept out by a radius in a given time, measured in radians. For one complete revolution, θ = 2π rad.
角位移 (θ) 是半径在一定时间内扫过的角度，单位是弧度。一整圈对应的角位移为 2π 弧度。
Angular velocity (ω) is the rate of change of angular displacement. It is related to the period T by ω = 2π/T and to linear speed v by v = ωr.
角速度 (ω) 是角位移随时间的变化率。它与周期 T 的关系为 ω = 2π/T，与线速度 v 的关系为 v = ωr。
ω = Δθ / Δt
Centripetal acceleration is the acceleration directed towards the centre of the circular path. Its magnitude is a = v²/r or a = ω²r, and it is responsible for changing the direction of velocity, not its magnitude.
向心加速度 是指向圆心的加速度。其大小为 a = v²/r 或 a = ω²r。它只改变速度的方向，不改变速度的大小。
Centripetal force is the resultant force acting on a body moving in a circle, directed towards the centre. It is not a separate force but the net force providing the centripetal acceleration: F = mv²/r = mω²r.
向心力 是作用在圆周运动物体上的指向圆心的合力。它不是一种独立的力，而是提供向心加速度的净力：F = mv²/r = mω²r。
Geostationary orbit is a circular equatorial orbit with a period of 24 hours, in which a satellite appears stationary relative to a point on the Earth’s surface. Its orbital radius is approximately 42 300 km from the Earth’s centre.
地球静止轨道 是一个周期为 24 小时的圆形赤道轨道，卫星相对于地面保持静止。该轨道半径距离地心约 42 300 km。
2. Gravitational Fields | 引力场
Gravitational field strength (g) at a point is the gravitational force per unit mass experienced by a small test mass placed at that point: g = F/m. Near the Earth’s surface, g ≈ 9.81 N kg⁻¹.
引力场强度 (g) 是放置在该点的小检验质量所受到的引力与质量的比值：g = F/m。在地球表面附近，g ≈ 9.81 N kg⁻¹。
Newton’s law of universal gravitation states that the force between two point masses is proportional to the product of their masses and inversely proportional to the square of their separation: F = Gm₁m₂/r², where G is the gravitational constant.
牛顿万有引力定律 指出，两个质点间的引力与它们的质量乘积成正比，与它们距离的平方成反比：F = Gm₁m₂/r²，其中 G 是引力常量。
Gravitational potential (φ) at a point is the work done per unit mass in bringing a small test mass from infinity to that point. For a point mass M, φ = -GM/r. The zero of potential is taken at infinity.
引力势 (φ) 是将单位质量从无穷远移到该点所做的功。对于点质量 M，φ = -GM/r。引力势的零点定义在无穷远处。
Escape velocity is the minimum speed an object must have at the surface of a planet to escape its gravitational field without further propulsion. It is given by v = √(2GM/R), where R is the planet’s radius.
逃逸速度 是物体在行星表面脱离其引力场而不需要继续推动的最小速度，公式为 v = √(2GM/R)，其中 R 是行星半径。
3. Simple Harmonic Motion (SHM) | 简谐运动
Simple harmonic motion is oscillatory motion in which the acceleration is directly proportional to the displacement from the equilibrium position and always directed towards it: a ∝ −x. The defining equation is a = −ω²x.
简谐运动 是一种加速度与偏离平衡位置的位移成正比且始终指向平衡位置的往复运动：a ∝ −x。定义方程为 a = −ω²x。
Displacement in SHM can be described by x = x₀ sin(ωt) or x = x₀ cos(ωt), where x₀ is the amplitude. Velocity v = ±ω√(x₀² − x²) and maximum speed vₛ = ωx₀.
简谐运动的位移 可以表示为 x = x₀ sin(ωt) 或 x = x₀ cos(ωt)，其中 x₀ 是振幅。速度 v = ±ω√(x₀² − x²)，最大速率 vₛ = ωx₀。
Period and frequency for a mass–spring system: T = 2π√(m/k); for a simple pendulum: T = 2π√(L/g), provided the amplitude is small. Frequency f = 1/T.
周期与频率 弹簧振子：T = 2π√(m/k)；单摆：T = 2π√(L/g)，前提是振幅很小。频率 f = 1/T。
Damping refers to the loss of energy from an oscillating system due to resistive forces. Light damping causes a gradual decrease in amplitude; critical damping returns the system to equilibrium in the shortest time without oscillating; heavy damping results in a very slow return to equilibrium.
阻尼 是指由于阻力使振动系统能量逐渐损失的现象。弱阻尼使振幅逐渐减小；临界阻尼使系统在最短时间内回到平衡位置而不产生振荡；过阻尼则使系统非常缓慢地返回平衡。
Resonance occurs when the driving frequency matches the natural frequency of the system, leading to a maximum amplitude of oscillation. The phase difference between the driver and the oscillator at resonance is π/2 rad.
共振 发生在驱动力频率等于系统固有频率时，此时振幅达到最大。共振时驱动与振动之间的相位差为 π/2 rad。
4. Thermal Physics | 热物理
Internal energy is the sum of the random kinetic and potential energies of the molecules in a substance. A change in internal energy ΔU is determined by the heat Q added to the system and the work W done on the system: ΔU = Q + W.
内能 是物质内部分子无规则运动的动能和分子间势能的总和。内能的变化 ΔU 由传给系统的热量 Q 和对系统做的功 W 决定：ΔU = Q + W。
Specific heat capacity (c) is the energy required to raise the temperature of 1 kg of a substance by 1 K without a change of state. Units: J kg⁻¹ K⁻¹.
比热容 (c) 是在无相变的情况下使 1 kg 物质温度升高 1 K 所需的能量。单位是 J kg⁻¹ K⁻¹。
Specific latent heat (L) is the energy needed to change the state of 1 kg of a substance at constant temperature. The latent heat of fusion (solid–liquid) and vaporisation (liquid–gas) are different.
比潜热 (L) 是温度保持不变时 1 kg 物质发生状态变化所需的能量。熔化潜热（固–液）与汽化潜热（液–气）数值不同。
The ideal gas equation connects pressure, volume, amount and temperature: pV = nRT = NkT, where n is the number of moles, R is the molar gas constant, N is the number of molecules, and k is the Boltzmann constant.
理想气体状态方程 将压强、体积、物质的量和温度联系起来：pV = nRT = NkT，其中 n 是摩尔数，R 是摩尔气体常数，N 是分子数，k 是玻尔兹曼常数。
Kinetic theory of gases relates the macroscopic pressure of a gas to the microscopic motion of its molecules: pV = ⅓ N m ⟨c²⟩, where ⟨c²⟩ is the mean square speed. The root-mean-square speed c_rms = √⟨c²⟩ = √(3kT/m).
气体动理论 将气体的宏观压强与微观分子运动联系起来：pV = ⅓ N m ⟨c²⟩，其中 ⟨c²⟩ 为均方速率。方均根速率 c_rms = √⟨c²⟩ = √(3kT/m)。
5. Electric Fields | 电场
Electric field strength (E) at a point is the force per unit positive charge exerted on a small test charge: E = F/q. For a uniform field between parallel plates, E = V/d.
电场强度 (E) 是单位正电荷在该点受到的电场力：E = F/q。对平行板间的匀强电场，E = V/d。
Coulomb’s law gives the force between two point charges: F = kQ₁Q₂/r², where k = 1/(4πε₀) in a vacuum. Like charges repel; unlike charges attract.
库仑定律 给出两点电荷间的力：F = kQ₁Q₂/r²，真空中 k = 1/(4πε₀)。同种电荷相斥，异种电荷相吸。
Electric potential (V) at a point is the work done per unit positive charge in bringing a small test charge from infinity to that point. For a point charge Q, V = kQ/r. Equipotential surfaces are perpendicular to field lines.
电势 (V) 是将单位正电荷从无穷远移到该点所做的功。对点电荷 Q，V = kQ/r。等势面与电场线处处垂直。
Capacitance (C) of a capacitor is the charge stored per unit potential difference: C = Q/V. The energy stored is U = ½ QV = ½ CV² = ½ Q²/C. The time constant τ = RC governs charging and discharging.
电容 (C) 是电容器储存的电荷与两极板间电势差的比值：C = Q/V。储存的能量 U = ½ QV = ½ CV² = ½ Q²/C。时间常数 τ = RC 决定充放电的快慢。
6. Magnetic Fields & Electromagnetic Induction | 磁场与电磁感应
Magnetic flux density (B) is a measure of the strength of a magnetic field. It can be defined via the force on a current-carrying conductor: F = BIL sinθ, where θ is the angle between the conductor and the field direction.
磁通量密度 (B) 是磁场强弱的量度。它可通过电流所受的力来定义：F = BIL sinθ，θ 是导线与磁场方向的夹角。
Magnetic force on a moving charge is given by F = Bqv sinθ. The direction of the force is perpendicular to both velocity and field, given by Fleming’s left‑hand rule (for conventional current).
运动电荷所受的磁力 为 F = Bqv sinθ。力方向垂直于速度和磁场方向，由弗莱明左手定则（对正电荷或传统电流）判定。
Magnetic flux (Φ) through a surface is Φ = BA cosθ, where θ is the angle between the field lines and the normal to the surface. Unit: weber (Wb). Flux linkage for a coil of N turns is NΦ.
磁通量 (Φ) 穿过一个面时，Φ = BA cosθ，θ 是磁感线与法线的夹角。单位是韦伯 (Wb)。N 匝线圈的磁链为 NΦ。
Faraday’s law of electromagnetic induction states that the induced e.m.f. in a circuit is directly proportional to the rate of change of magnetic flux linkage: ε = −N(dΦ/dt). Lenz’s law gives the minus sign, indicating that the induced current opposes the change causing it.
法拉第电磁感应定律 指出，电路中感应电动势与磁链的变化率成正比：ε = −N(dΦ/dt)。负号体现楞次定律，即感应电流的方向总是阻碍引起它的磁通变化。
7. Alternating Current | 交流电
Root-mean-square (rms) value of an alternating current or voltage is the equivalent direct current/voltage that would deliver the same average power to a resistor. For a sinusoidal waveform, V_rms = V₀/√2 and I_rms = I₀/√2.
方均根（rms）值 是产生相同平均功率的等效直流值。对正弦波形，V_rms = V₀/√2，I_rms = I₀/√2。
An ideal transformer obeys the relationships V_s/V_p = N_s/N_p and, assuming 100% efficiency, I_p V_p = I_s V_s. Step‑up transformers increase voltage and decrease current; step‑down transformers do the opposite.
理想变压器 满足 V_s/V_p = N_s/N_p，且假设效率为 100% 时 I_p V_p = I_s V_s。升压变压器提高电压、降低电流；降压变压器反之。
Rectification converts alternating current to direct current. Half‑wave rectification uses a single diode; full‑wave rectification typically uses a bridge rectifier. Smoothing is achieved by capacitors to reduce the ripple.
整流 将交流电转换为直流电。半波整流使用一个二极管；全波整流常用桥式整流器。通过电容滤波可减小纹波。
8. Quantum Physics | 量子物理
Photon is a quantum of electromagnetic radiation. The energy of a photon is E = hf = hc/λ, where h is Planck’s constant. Photon momentum is p = E/c = h/λ.
光子 是电磁辐射的量子。光子能量 E = hf = hc/λ，h 是普朗克常数。光子动量为 p = E/c = h/λ。
Photoelectric effect is the emission of electrons from a metal surface when light of sufficiently high frequency is incident on it. Einstein’s photoelectric equation is hf = Φ + ½ mv²_max, where Φ is the work function, the minimum energy needed to liberate an electron.
光电效应 是当频率足够高的光照射金属表面时，电子被发射出来的现象。爱因斯坦光电方程为 hf = Φ + ½ mv²_max，其中 Φ 为逸出功，即释放一个电子所需的最小能量。
Threshold frequency (f₀) is the minimum frequency of incident light required to cause photoemission; below this frequency, no electrons are emitted regardless of intensity. hf₀ = Φ.
截止频率 (f₀) 是引起光电发射所需的最低入射光频率；低于此频率，无论光强多大都不会有电子逸出。hf₀ = Φ。
Wave–particle duality states that all particles exhibit both wave and particle properties. The de Broglie wavelength of a particle is λ = h/p, where p is its momentum. Electron diffraction provides evidence for this duality.
波粒二象性 表明一切粒子都具有波和粒子的双重性质。粒子的德布罗意波长为 λ = h/p，p 为动量。电子衍射为这一性质提供了证据。
Energy levels and spectra: Electrons in atoms occupy discrete energy levels. A photon is emitted when an electron makes a transition from a higher to a lower level: hf = E₂ − E₁. Line spectra thus characterise the element.
能级与光谱：原子中的电子处于分立的能级上。当电子从高能级跃迁到低能级时会发射光子：hf = E₂ − E₁。因此线状谱可用于鉴别元素。
9. Nuclear Physics | 核物理
Mass defect is the difference between the mass of a nucleus and the sum of the masses of its individual nucleons. It is converted into binding energy according to E = mc².
质量亏损 是原子核的质量与其单独核子质量总和之差。根据 E = mc²，质量亏损转化为结合能。
Binding energy of a nucleus is the energy required to separate it into its individual protons and neutrons. Binding energy per nucleon peaks around iron‑56 and indicates nuclear stability.
结合能 是将原子核拆分成单个质子和中子所需的能量。比结合能（每个核子的结合能）在铁‑56 附近达到峰值，反映了核的稳定性。
Radioactive decay follows an exponential law: N = N₀ e⁻λt, where λ is the decay constant. Activity A = λN. The half‑life T₁/₂ is the time for half the nuclei to decay: T₁/₂ = ln2 / λ.
放射性衰变 遵循指数规律：N = N₀ e⁻λt，λ 是衰变常量。活度 A = λN。半衰期 T₁/₂ 是半数原子核衰变所需的时间：T₁/₂ = ln2 / λ。
Nuclear fission is the splitting of a heavy nucleus into two lighter nuclei, accompanied by the release of energy and neutrons. Nuclear fusion is the merging of light nuclei to form a heavier nucleus, also releasing energy. Both processes involve a change in binding energy per nucleon.
核裂变 是一个重核分裂成两个较轻核，同时释放能量和中子的过程。核聚变 是轻核结合成较重核的过程，同样释放能量。两种过程都伴随比结合能的变化。
10. Medical Physics (Optional Topic) | 医学物理（选修专题）
X‑ray production: When fast electrons are decelerated by a metal target, X‑rays are produced via bremsstrahlung (braking radiation) and characteristic radiation. The minimum wavelength λ_min = hc/eV, where V is the tube voltage.
X 射线产生：高速电子被金属靶减速时，通过轫致辐射和特征辐射产生 X 射线。最短波长 λ_min = hc/eV，V 为管电压。
Attenuation of X‑rays: The intensity I of a parallel beam decreases exponentially with thickness x: I = I₀ e⁻μx, where μ is the linear attenuation coefficient. Half‑value thickness x₁/₂ = ln2/μ.
X 射线的衰减：平行射束的强度随厚度 x 指数衰减：I = I₀ e⁻μx，μ 是线性衰减系数。半值厚度 x₁/₂ = ln2/μ。
Ultrasound uses high‑frequency sound waves above 20 kHz. The acoustic impedance Z = ρc determines reflection at tissue boundaries. The intensity reflection coefficient for normal incidence is (Z₂ − Z₁)²/(Z₂ + Z₁)².
超声 使用高于 20 kHz 的高频声波。声阻抗 Z = ρc 决定了组织界面处的反射。正入射时的声强反射系数为 (Z₂ − Z₁)²/(Z₂ + Z₁)²。
Positron emission tomography (PET) relies on the annihilation of a positron and an electron, producing two 511 keV gamma photons travelling in opposite directions. Detection of coincident photons enables the reconstruction of metabolic activity images.
正电子发射断层扫描 (PET) 依赖正电子与电子湮灭，产生两个方向相反、能量均为 511 keV 的光子。通过符合探测可重建组织代谢活动的图像。
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