📚 OCR A-Level Physics Year 13: Key Terminology Quick Reference Guide | Year 13 OCR 物理：词汇术语速记指南
Mastering specialist terminology is the key to unlocking high marks in OCR A-Level Physics. This guide covers essential terms from circular motion, gravitational fields, thermal physics, nuclear and particle physics, medical imaging and more. Each concept is presented with a clear English definition followed by its precise Chinese equivalent, helping you build confidence for both written explanations and multiple-choice questions.
掌握专业术语是解锁 OCR A-Level 物理高分的关键。本指南涵盖了圆周运动、引力场、热物理、核与粒子物理、医学成像等核心领域的重要术语。每个概念均提供清晰的英文定义和准确的中文对应，帮助你为文字解释题和选择题建立信心。
1. Circular Motion Terminology | 圆周运动术语
Angular displacement (θ) is the angle through which an object moves in a circular path, measured in radians. One radian is the angle subtended at the centre of a circle by an arc equal in length to the radius.
角位移（θ）是物体在圆周路径中转过的角度，单位为弧度（rad）。一弧度是指圆弧长度等于半径时所对的圆心角。
Angular velocity (ω) is the rate of change of angular displacement, calculated as ω = Δθ/Δt or ω = 2πf. It is measured in rad s⁻¹.
角速度（ω）是角位移的变化率，计算式为 ω = Δθ/Δt 或 ω = 2πf，单位为 rad s⁻¹。
Centripetal acceleration (a) is the acceleration of an object moving at constant speed in a circle. It is directed towards the centre of the circle and has magnitude a = v²/r or a = ω²r.
向心加速度（a）是物体在匀速圆周运动中的加速度，方向指向圆心，大小为 a = v²/r 或 a = ω²r。
Centripetal force (F) is the net force required to keep an object moving in a circular path. It acts towards the centre of the circle and is given by F = mv²/r or F = mω²r.
向心力（F）是维持物体做圆周运动所需的净力，方向指向圆心，由 F = mv²/r 或 F = mω²r 给出。
2. Simple Harmonic Motion Terminology | 简谐运动术语
Simple harmonic motion (SHM) is oscillatory motion where the acceleration is directly proportional to the displacement from the equilibrium position and is always directed towards that equilibrium point. Mathematically, a = −ω²x.
简谐运动（SHM）是一种振荡运动，其加速度与离开平衡位置的位移成正比，且始终指向平衡点。数学表达为 a = −ω²x。
Amplitude (A) is the maximum displacement from the equilibrium position. The total energy of an undamped SHM system is proportional to A².
振幅（A）是离开平衡位置的最大位移。无阻尼简谐运动系统的总能量与 A² 成正比。
Free and forced oscillations: free oscillations occur when a system oscillates at its natural frequency without external driving force. Forced oscillations occur when a periodic external force is applied, and if the driving frequency matches the natural frequency, resonance occurs, causing a dramatic increase in amplitude.
自由振荡与受迫振荡：自由振荡是系统以其固有频率振动且无外部驱动力。受迫振荡则有周期性外力作用；当驱动频率等于固有频率时发生共振，振幅急剧增大。
Damping refers to the dissipation of energy from an oscillating system. Light damping gradually reduces amplitude; critical damping returns the system to equilibrium in the shortest time without overshoot; heavy damping results in a slow return.
阻尼指振荡系统中能量的耗散。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且无超调；过阻尼则导致缓慢返回。
3. Gravitational Field Terminology | 引力场术语
Gravitational field strength (g) is the force per unit mass experienced by a small test mass placed in the field. It is a vector quantity pointing towards the centre of the mass causing the field. Near a point mass or outside a sphere, g = GM/r².
引力场强度（g）是置于场中的小检验质量所受的力除以其质量。它是矢量，指向产生场的质量中心。在点质量或球体外部，g = GM/r²。
Gravitational potential (V) at a point is the work done per unit mass to bring a small test mass from infinity to that point. It is negative because gravity is attractive; for a point mass, V = −GM/r. The zero of potential is at infinity.
引力势（V）是单位质量从无限远移至该点所做的功。由于引力为吸引力，势为负值；对于点质量，V = −GM/r。势的零点在无穷远处。
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 derived from equating kinetic energy to gravitational potential energy: v_esc = √(2GM/R).
逃逸速度是物体在行星表面脱离引力场而不需进一步推进所需的最小速率。由动能等于引力势能推导：v_esc = √(2GM/R)。
Geostationary orbit is a circular orbit above Earth’s equator with a period of 24 hours, so the satellite appears stationary relative to the Earth’s surface. The orbital radius is approximately 4.2 × 10⁷ m from Earth’s centre.
地球同步轨道是位于赤道上空、周期为 24 小时的圆轨道，使卫星相对于地面静止。轨道半径约为地心起 4.2 × 10⁷ m。
4. Thermal Physics Terminology | 热物理术语
Internal energy is the sum of the randomly distributed kinetic and potential energies of all the particles in a substance. A change in internal energy ΔU is given by ΔU = Q + W, where Q is the heat added to the system and W is the work done on the system (first law of thermodynamics).
内能是物质中所有粒子随机分布的动能和势能之和。内能变化 ΔU 由 ΔU = Q + W 给出，其中 Q 是系统吸收的热量，W 是对系统做的功（热力学第一定律）。
Specific heat capacity (c) is the energy needed to raise the temperature of 1 kg of a substance by 1 K without a change of state. Units are J kg⁻¹ K⁻¹. The energy transferred is Q = mcΔθ.
比热容（c）是使 1 kg 物质温度升高 1 K 而不发生物态变化所需的能量，单位为 J kg⁻¹ K⁻¹。热量传递为 Q = mcΔθ。
Specific latent heat (L) is the energy required to change the state of 1 kg of a substance at constant temperature. Latent heat of fusion is for melting/freezing; latent heat of vaporisation is for boiling/condensing. Q = mL.
比潜热（L）是在恒定温度下使 1 kg 物质改变状态所需的能量。熔化/凝固对应熔解潜热；汽化/液化对应汽化潜热。Q = mL。
Absolute zero (0 K) is the temperature at which substances have minimum internal energy. It is the zero point of the thermodynamic temperature scale and equals −273.15 °C. The ideal gas law breaks down near absolute zero.
绝对零度（0 K）是物质内能最低时的温度，为热力学温标的零点，等于 −273.15 °C。在绝对零度附近理想气体定律不再适用。
5. Electric Field Terminology | 电场术语
Electric field strength (E) is the force per unit positive charge exerted on a stationary test charge placed at a point. For a point charge, E = Q/(4πε₀r²). It is a vector, and field lines point away from positive charges and towards negative charges.
电场强度（E）是单位正电荷在该点所受的力。对于点电荷，E = Q/(4πε₀r²)。它是矢量，电场线从正电荷发出指向负电荷。
Electric potential (V) is the work done per unit positive charge to move a test charge from infinity to a point in the field. For a point charge, V = Q/(4πε₀r). Equipotential surfaces are always perpendicular to field lines.
电势（V）是将单位正电荷从无穷远移动到电场中某点所做的功。对于点电荷，V = Q/(4πε₀r)。等势面始终垂直于电场线。
Capacitance (C) is the charge stored per unit potential difference across a capacitor: C = Q/V. The unit is the farad (F). In a parallel plate capacitor, C = ε₀εᵣA/d, where εᵣ is the relative permittivity of the dielectric.
电容（C）是电容器每单位电势差所储存的电荷量：C = Q/V，单位为法拉（F）。对于平行板电容器，C = ε₀εᵣA/d，其中 εᵣ 为介质的相对电容率。
Time constant (τ) for a capacitor-resistor circuit is the product RC. It represents the time taken for the charge or voltage to fall to 1/e (about 37%) of its initial value during discharge, or to rise to (1 − 1/e) of the final value during charging.
时间常数（τ）对于电容-电阻电路，是 R 与 C 的乘积（RC）。它表示放电时电荷或电压降至初始值的 1/e（约 37%）所需的时间，或充电时升至最终值的（1 − 1/e）所需的时间。
6. Magnetic Field and Electromagnetic Induction Terminology | 磁场与电磁感应术语
Magnetic flux density (B) is a measure of the strength of a magnetic field, defined by the force on a current-carrying conductor: F = BIL sinθ. The unit is the tesla (T). It can also be thought of as the number of magnetic field lines passing through a unit area perpendicular to the field.
磁通量密度（B）是磁场强度的量度，由电流受力定义：F = BIL sinθ，单位为特斯拉（T）。也可理解为单位面积内垂直于磁场的磁感线数目。
Magnetic flux (Φ) is the product of magnetic flux density and the area perpendicular to the field: Φ = BA cosθ. It is measured in webers (Wb). Magnetic flux linkage is NΦ for a coil of N turns.
磁通量（Φ）是磁通量密度与垂直于磁场的面积的乘积：Φ = BA cosθ，单位为韦伯（Wb）。对于一个 N 匝线圈，磁链为 NΦ。
Faraday’s law of electromagnetic induction states that the magnitude of the induced e.m.f. is equal to the rate of change of magnetic flux linkage: ε = −d(NΦ)/dt. Lenz’s law gives the minus sign, indicating that the induced current opposes the change producing it.
法拉第电磁感应定律指出，感应电动势的大小等于磁链的变化率：ε = −d(NΦ)/dt。楞次定律给出了负号，表示感应电流反抗引起它的磁通变化。
Transformer operation is based on a changing magnetic flux in a primary coil inducing an e.m.f. in a secondary coil linked by the same iron core. For an ideal transformer, V_s/V_p = N_s/N_p and power in primary equals power in secondary.
变压器的工作基于初级线圈中变化磁通在同一铁芯连接的次级线圈中感应出电动势。理想变压器满足 V_s/V_p = N_s/N_p，且初级功率等于次级功率。
7. Nuclear Physics Terminology | 核物理术语
Mass defect is the difference between the mass of a nucleus and the sum of the masses of its individual nucleons. This ‘missing’ mass has been converted into binding energy according to E = mc².
质量亏损是原子核的质量与其各个核子质量总和之间的差值。这部分“缺失”的质量根据 E = mc² 转化为结合能。
Binding energy of a nucleus is the energy required to separate the nucleus into its constituent protons and neutrons. Binding energy per nucleon is a measure of nuclear stability; iron-56 has one of the highest values.
结合能是把原子核拆分成其组成的质子和中子所需的能量。每个核子的结合能是核稳定性的量度；铁-56 具有最高的每核子结合能之一。
Activity (A) is the rate at which a radioactive source decays, measured in becquerels (Bq), where 1 Bq = 1 decay per second. Activity follows the exponential law A = λN, where λ is the decay constant.
活度（A）是放射源衰变的速率，单位为贝克勒尔（Bq），1 Bq = 每秒衰变一次。活度遵循指数规律 A = λN，λ 为衰变常量。
Half-life (T½) is the average time taken for half the nuclei in a sample to decay, or for the activity to halve. It is related to the decay constant by T½ = ln 2/λ.
半衰期（T½）是样本中一半的原子核发生衰变或活度减半所需的平均时间。它与衰变常量的关系为 T½ = ln 2/λ。
8. Particle Physics Terminology | 粒子物理术语
Hadrons are particles made of quarks and experience the strong nuclear force. They are subdivided into baryons (three quarks, e.g. proton uud, neutron udd) and mesons (quark–antiquark pair, e.g. pion).
强子是由夸克组成的粒子，参与强相互作用。它们分为重子（三个夸克，如质子 uud、中子 udd）和介子（夸克-反夸克对，如 π 介子）。
Leptons are fundamental particles that do not experience the strong force. The electron, muon, tau and their associated neutrinos are leptons. Lepton number is conserved in interactions.
轻子是不参与强相互作用的基本粒子。电子、μ 子、τ 子及相应的中微子都是轻子。轻子数在相互作用中守恒。
Quark confinement refers to the fact that quarks cannot exist in isolation; they are always bound within hadrons. Attempting to separate them produces new quark–antiquark pairs.
夸克禁闭指夸克不能单独存在，总是被束缚在强子内部。试图分开夸克会产生新的夸克-反夸克对。
Exchange particles (gauge bosons) mediate the fundamental forces: photons for the electromagnetic force, W⁺, W⁻ and Z⁰ bosons for the weak force, and gluons for the strong force. The electromagnetic and weak forces are unified into the electroweak theory.
交换粒子（规范玻色子）传递基本相互作用：光子传递电磁力，W⁺、W⁻ 和 Z⁰ 玻色子传递弱力，胶子传递强力。电磁作用与弱作用被统一为电弱理论。
9. Medical Imaging Terminology | 医学成像术语
Intensity of X-rays after passing through a material follows an exponential attenuation law: I = I₀ e^(−μx), where μ is the attenuation coefficient and x is the thickness. Half-value thickness (HVT) is the thickness needed to reduce intensity by half: x½ = ln 2/μ.
X 射线强度穿过材料后遵循指数衰减规律：I = I₀ e^(−μx)，其中 μ 为衰减系数，x 为厚度。半值厚度（HVT）是使强度减半所需的厚度：x½ = ln 2/μ。
Ultrasound uses high-frequency sound waves. The acoustic impedance Z of a material is Z = ρc, where ρ is density and c is speed of sound. At boundaries where impedances differ, part of the wave is reflected. The reflection coefficient is (Z₂ − Z₁)²/(Z₂ + Z₁)².
超声波使用高频声波。材料的声阻抗 Z = ρc，ρ 为密度，c 为声速。在阻抗不同的界面，部分波被反射。反射系数为 (Z₂ − Z₁)²/(Z₂ + Z₁)²。
Positron Emission Tomography (PET) relies on pair annihilation. A positron meets an electron, producing two gamma photons of energy 511 keV each, travelling in opposite directions. This allows the location of the annihilation to be reconstructed.
正电子发射断层成像（PET）基于正负电子对湮灭。正电子与电子相遇，产生两个能量各为 511 keV 的光子，沿相反方向运动，从而可以重建湮灭发生的位置。
Magnetic Resonance Imaging (MRI) uses a strong magnetic field to align protons in the body. Radio frequency pulses tip the protons out of alignment, and as they relax back, they emit signals that are used to construct images. The Larmor frequency determines the resonance condition.
磁共振成像（MRI）利用强磁场使体内质子对齐。射频脉冲使质子偏离，当它们恢复时发射信号，用以构建图像。拉莫尔频率决定共振条件。
10. Astrophysics and Cosmology Terminology | 天体物理与宇宙学术语
Standard candle is an astronomical object of known luminosity. Cepheid variable stars and Type Ia supernovae are used to measure astronomical distances through the inverse square law of brightness: F = L/(4πd²).
标准烛光是已知光度的天体。造父变星和 Ia 型超新星被用来通过亮度与距离平方反比律 F = L/(4πd²) 测量天文距离。
Doppler shift (redshift) for light is expressed as z = Δλ/λ₀ ≈ v/c for non-relativistic speeds. A redshift indicates the source is moving away; a blueshift indicates it is approaching. Hubble’s law v = H₀d shows that the speed of recession of a galaxy is proportional to its distance, providing evidence for the expanding universe.
光的多普勒频移（红移）非相对论速度下表示为 z = Δλ/λ₀ ≈ v/c。红移表明光源正在远离；蓝移表明靠近。哈勃定律 v = H₀d 表明星系退行速度与其距离成正比，为宇宙膨胀提供了证据。
Cosmic Microwave Background (CMB) radiation is the remnant thermal radiation from the Big Bang, now at a temperature of approximately 2.7 K. It is almost isotropic, with tiny temperature fluctuations that correspond to the seeds of galaxy formation.
宇宙微波背景辐射（CMB）是大爆炸后遗留下来的热辐射，现在温度约为 2.7 K。它几乎是各向同性的，微小的温度涨落对应星系形成的种子。
Dark energy is a hypothetical form of energy that permeates space and is thought to be responsible for the accelerated expansion of the universe. It constitutes about 68% of the total energy density of the universe.
暗能量是一种假设的充斥空间的能量形式，被认为是宇宙加速膨胀的原因，约占宇宙总能量密度的 68%。
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