📚 Physics Revision Guide: Core Concepts & Exam Tips | 物理复习指南：核心概念与考试技巧
Physics is the science of understanding the natural world, from the smallest particles to the largest galaxies. This revision guide condenses the core topics you need for exams, focusing on key definitions, formulas, and common pitfalls.
物理是一门理解自然世界的科学，从最小的粒子到最大的星系。本复习指南浓缩了考试所需的核心主题，聚焦关键定义、公式和常见易错点。
1. Measurement and Units | 测量与单位
All physical quantities consist of a numerical value and a unit. The SI system provides seven base units, including metre (m), kilogram (kg), second (s), ampere (A), kelvin (K), mole (mol), and candela (cd).
所有物理量都由数值和单位组成。国际单位制（SI）规定了七个基本单位，包括米（m）、千克（kg）、秒（s）、安培（A）、开尔文（K）、摩尔（mol）和坎德拉（cd）。
Prefixes are used to represent powers of ten. For example, 1 km = 10³ m, 1 mm = 10⁻³ m, 1 μs = 10⁻⁶ s, and 1 nm = 10⁻⁹ m.
词头用于表示十的幂次。例如，1 千米 = 10³ 米，1 毫米 = 10⁻³ 米，1 微秒 = 10⁻⁶ 秒，1 纳米 = 10⁻⁹ 米。
- Always convert to base units before calculation.
- 在计算前务必转换为基本单位。
- Use significant figures consistently with the data given.
- 有效数字的位数要与题目所给数据保持一致。
Uncertainty Δx = (absolute uncertainty) | 不确定度 Δx = （绝对不确定度）
When adding or subtracting measurements, absolute uncertainties add; when multiplying or dividing, percentage uncertainties add.
当测量值相加或相减时，绝对不确定度相加；当相乘或相除时，百分比不确定度相加。
2. Kinematics | 运动学
Kinematics describes motion without considering its causes. Key quantities are displacement (s), velocity (v), acceleration (a), and time (t).
运动学描述运动而不考虑运动的原因。关键量为位移（s）、速度（v）、加速度（a）和时间（t）。
v = u + at
s = ut + ½at²
v² = u² + 2as
These equations apply only when acceleration is constant. Remember that displacement and velocity are vectors — direction matters.
这些公式仅适用于加速度恒定的情况。请记住，位移和速度是矢量——方向很重要。
- In free fall, a = g = 9.81 m/s² downward.
- 在自由落体中，a = g = 9.81 m/s²，方向向下。
- At the highest point of projectile motion, vertical velocity is zero.
- 在抛体运动的最高点，竖直速度为零。
3. Forces and Newton’s Laws | 力与牛顿定律
A force is a push or pull that changes an object’s motion. Newton’s first law states that an object stays at rest or moves at constant velocity unless acted on by a net force.
力是改变物体运动状态的推或拉。牛顿第一定律指出，若不受合外力，物体将保持静止或匀速直线运动状态。
F = ma (Newton’s second law) | F = ma （牛顿第二定律）
Newton’s third law: every action has an equal and opposite reaction. These forces act on different objects, so they never cancel each other.
牛顿第三定律：每一个作用力都有一个大小相等、方向相反的反作用力。这两个力作用在不同物体上，因此永远不会相互抵消。
Friction, normal reaction, tension, and weight are common forces. Weight = mg, where g is the gravitational field strength (9.81 N/kg on Earth).
摩擦力、支持力、张力和重力是常见力。重力 G = mg，其中 g 是重力场强度（地球表面为 9.81 N/kg）。
4. Work, Energy, and Power | 功、能量与功率
Work is done when a force moves an object through a distance. Energy is the capacity to do work, and power is the rate of doing work.
当力使物体移动一段距离时，就做了功。能量是做功的能力，功率是做功的快慢。
W = Fd cosθ
Eₖ = ½mv²
Eₚ = mgh
P = W/t = Fv
Mechanical energy is conserved in the absence of friction: the sum of kinetic and potential energy remains constant.
在没有摩擦的情况下，机械能守恒：动能与势能之和保持不变。
- Efficiency = (useful output energy / total input energy) × 100%.
- 效率 =（有用输出能量 / 总输入能量）× 100%。
- Power is measured in watts (W), where 1 W = 1 J/s.
- 功率的单位是瓦特（W），1 瓦特 = 1 焦耳/秒。
5. Momentum and Collisions | 动量与碰撞
Momentum is the product of mass and velocity. It is a vector quantity. The law of conservation of momentum states that total momentum of an isolated system remains constant.
动量是质量与速度的乘积，是矢量。动量守恒定律指出，孤立系统的总动量保持不变。
p = mv
Δp = FΔt (impulse) | p = mv
Δp = FΔt （冲量）
In elastic collisions, both momentum and kinetic energy are conserved. In inelastic collisions, momentum is conserved but some kinetic energy is converted into heat or sound.
在弹性碰撞中，动量和动能均守恒。在非弹性碰撞中，动量守恒，但部分动能转化为热能或声能。
6. Thermal Physics | 热学
Thermal energy transfers from hotter regions to cooler regions. Temperature measures the average kinetic energy of particles, while heat is the total energy transferred.
热能总是从高温区域传递到低温区域。温度衡量粒子平均动能的大小，而热量是传递的总能量。
Q = mcΔT
Q = mL (latent heat) | Q = mcΔT
Q = mL （潜热）
The specific heat capacity c is the energy needed to raise 1 kg of a substance by 1 K. Specific latent heat L is the energy needed to change the state of 1 kg without changing temperature.
比热容 c 是使 1 千克物质升高 1 开尔文所需的能量。比潜热 L 是使 1 千克物质在温度不变的情况下改变状态所需的能量。
Heat transfer occurs via conduction, convection, and radiation. Conduction involves particle collisions; convection involves bulk fluid movement; radiation is via electromagnetic waves.
热传递方式有传导、对流和辐射。传导涉及粒子碰撞；对流涉及流体整体运动；辐射通过电磁波进行。
7. Waves and Light | 波动与光
Waves transfer energy without transferring matter. They can be transverse (like light) or longitudinal (like sound). Key properties include wavelength λ, frequency f, and speed v.
波传递能量而不传递物质。波可以是横波（如光）或纵波（如声）。关键性质包括波长 λ、频率 f 和速度 v。
v = fλ
Reflection, refraction, and diffraction are fundamental wave behaviours. The law of reflection states that the angle of incidence equals the angle of reflection.
反射、折射和衍射是基本的波动行为。反射定律指出入射角等于反射角。
- When light enters a denser medium, it bends towards the normal.
- 当光进入光密介质时，会向法线方向偏折。
- Total internal reflection occurs when the angle of incidence exceeds the critical angle.
- 当入射角超过临界角时，会发生全内反射。
8. Electricity | 电学
Electric current is the rate of flow of charge. Resistance opposes current flow. Ohm’s law states that the potential difference across a conductor is proportional to the current if temperature is constant.
电流是电荷流动的速率。电阻阻碍电流流动。欧姆定律指出，在温度恒定时，导体两端的电势差与电流成正比。
I = Q/t
V = IR
P = VI = I²R = V²/R
In series circuits, current is the same through each component and voltages add. In parallel circuits, voltage is the same across each branch and currents add.
在串联电路中，通过每个元件的电流相同，电压相加。在并联电路中，每个支路的电压相同，电流相加。
Resistors in series: R_total = R₁ + R₂ + …; in parallel: 1/R_total = 1/R₁ + 1/R₂ + …
串联电阻：R_total = R₁ + R₂ + …；并联电阻：1/R_total = 1/R₁ + 1/R₂ + …
9. Magnetism and Electromagnetism | 磁学与电磁学
Magnetic fields are created by moving charges or permanent magnets. Like poles repel, unlike poles attract. The direction of a magnetic field is from north to south.
磁场由运动的电荷或永磁体产生。同名磁极相斥，异名磁极相吸。磁场方向是从北极到南极。
F = BIL sinθ (force on a current-carrying wire)
A changing magnetic flux induces an electromotive force (emf) in a coil. This is Faraday’s law of electromagnetic induction. Lenz’s law gives the direction of the induced current.
变化的磁通量在线圈中感应出电动势（emf）。这就是法拉第电磁感应定律。楞次定律给出了感应电流的方向。
- Transformers use alternating current and electromagnetic induction to change voltage levels.
- 变压器利用交流电和电磁感应来改变电压等级。
- Step-up transformers increase voltage, step-down transformers decrease voltage.
- 升压变压器升高电压，降压变压器降低电压。
10. Modern Physics | 现代物理
The photoelectric effect demonstrates that light behaves as particles called photons. The energy of a photon is proportional to its frequency.
光电效应表明光表现为称为光子的粒子。光子的能量与其频率成正比。
E = hf
The de Broglie wavelength links a particle’s momentum to a wave-like wavelength: λ = h/p. This wave-particle duality is central to quantum physics.
德布罗意波长将粒子的动量与类似波的波长联系起来：λ = h/p。这种波粒二象性是量子物理的核心。
In nuclear physics, Einstein’s mass-energy equivalence shows that mass can be converted into energy: E = mc². Nuclear fission splits heavy nuclei, while fusion joins light nuclei.
在核物理中，爱因斯坦的质能等价关系表明质量可以转化为能量：E = mc²。核裂变使重核分裂，核聚变使轻核结合。
- Radioactive decay is random but follows exponential decay: N = N₀e^(−λt).
- 放射性衰变是随机的，但遵循指数衰减规律：N = N₀e^(−λt)。
- Activity is measured in becquerels (Bq).
- 放射性活度的单位是贝克勒尔（Bq）。
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