AS Physics: Last-Minute Revision Notes | AS 物理：考前冲刺笔记

📚 AS Physics: Last-Minute Revision Notes | AS 物理：考前冲刺笔记

Welcome to this ultimate last-minute revision guide for AS Physics. It . This article summarises the key concepts, equations, and practical insights you need to to ace your exam. Use these notes to refresh before the exam, covering mechanics, waves, electricity, quantum physics, and experimental skills.

欢迎使用这份 AS 物理终极考前冲刺笔记。本文总结了考试前需要快速回顾的核心概念、关键方程和实验要点，涵盖力学、波动、电学、量子物理与实验技能。

1. Kinematics | 运动学

Kinematics describes motion using displacement, velocity, and acceleration. The four SUVAT equations are vital for solving uniform acceleration problems. Always define a positive direction before tackling a problem.

运动学用位移、速度和加速度来描述运动。四个 SUVAT 方程是解决匀加速问题的关键。解题前务必规定正方向。

v = u + a t

s = u t + ½ a t²

s = ½ (u + v) t

v² = u² + 2 a s

on under gravity, a = g = 9.81 m s⁻² downwards; in many questions g is taken as 9.8 m s⁻².

符号含义：位移 s、初速度 u、末速度 v、加速度 a、时间 t。在重力作用下的竖直运动中，a = g = 9.81 m s⁻² 方向向下；许多题目取 g = 9.8 m s⁻²。

ting horizontal and vertical motion: horizontal velocity is constant, while vertical motion uses SUVAT with a = g.

在速度-时间图中，斜率表示加速度，图线下方面积表示位移。抛体运动通过分解水平与竖直运动处理：水平速度恒定，竖直运动使用含 a = g 的 SUVAT 方程。

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2. Dynamics and Forces | 动力学与力

Newton' n II: F = m a. Newton III: action and reaction are equal and opposite but act on different bodies.

牛顿定律是动力学的基础。牛顿第一定律：无合外力时物体保持静止或匀速直线运动。牛顿第二定律：F = m a。牛顿第三定律：作用力与反作用力大小相等、方向相反，但作用于不同物体。

F = m a

W = m g

Moment = F × d

, and friction. Friction can be static or dynamic; dynamic friction is often modelled as F_f = μ R, where μ is the coefficient of friction and R is the normal reaction.

受力图有助于隔离分析各力。常见力包括重力 W = m g、支持力、张力和摩擦力。摩擦力分静摩擦和动摩擦；动摩擦常建模为 F_f = μ R，其中 μ 为摩擦系数，R 为正压力。

rpendicular distance from the pivot, where d is the perpendicular distance from the pivot to the line of action of the force. The centre of gravity is the point where the entire weight appears to act.

平衡条件是合外力为零且合力矩为零。力矩 = 力 × 力臂，其中 d 为转轴到力作用线的垂直距离。重心是物体全部重量看似集中的点。

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3. Work, Energy and Power | 功、能与功率

W = F s cos θ. Energy is the capacity to do work, and it is conserved in isolated systems.

力使物体发生位移时做功。若力与位移成 θ 角，则用 W = F s cos θ。能量是做功的本领，在孤立系统中能量守恒。

W = F s cos θ

E_k = ½ m v²

E_p = m g h

P = W / t = F v

Kinetic energy depends on mass and speed squared. Gravitational potential energy near the Earth's surface is m g h. Power is the rate of energy transfer or work done. Efficiency compares useful output energy with total input energy.

动能取决于质量和速度的平方。地球表面附近的重力势能为 m g h。功率是能量传递或做功的速率。效率比较有用输出能量与总输入能量。

efficiency = useful output energy ÷ total input energy × 100%

s not isolated, energy may be transferred to thermal stores by friction or air resistance.

考试计算时，先判断题目要求能量、功率还是效率。注意单位：1 kW = 1000 W，1 MJ = 1 × 10⁶ J。若系统不孤立，能量可能因摩擦或空气阻力转移到热库。

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4. Momentum and Collisions | 动量与碰撞

tion matters. The principle of conservation of momentum states that total momentum in a closed system remains constant before and after a collision or explosion.

动量是质量与速度的乘积：p = m v。它是矢量，因此方向很重要。动量守恒定律指出，在封闭系统中，碰撞或爆炸前后的总动量保持不变。

p = m v

F Δt = Δp

Impulse is the product of force and the time for which it acts, and it equals the change in momentum. This explains why airbags and crumple zones reduce injury: they increase the collision time, so the force on passengers is reduced.

冲量是力与作用时间的乘积，等于动量的变化量。这解释了安全气囊和溃缩区为何能减少伤害：它们延长碰撞时间，从而减小乘客所受的力。

In elastic collisions, both momentum and kinetic energy are conserved. In inelastic collisions, momentum is conserved but kinetic energy is not; some kinetic energy is transferred to thermal energy, sound, or deformation. In explosions, total momentum before is often zero, so the fragments move in opposite directions with equal total momentum.

弹性碰撞中，动量和动能都守恒。非弹性碰撞中，动量守恒但动能不守恒；部分动能转化为热能、声能或形变能。爆炸中，爆炸前总动量常为零，因此碎片以大小相等、方向相反的总动量运动。

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5. Materials: Stress, Strain and Young Modulus | 材料：应力、应变与杨氏模量

For a stretched wire or spring, Hooke' orce, provided the elastic limit is not exceeded: F = k x, where k is the spring constant.

对于拉伸的金属丝或弹簧，胡克定律指出，在不超过弹性极限时，伸长量与外力成正比：F = k x，其中 k 为劲度系数。

F = k x

stress = F / A

strain = ΔL / L

E = stress / strain = F L / (A ΔL)

Stress is force per unit cross-sectional area, measured in Pa. Strain is the fractional change in length and has no unit. Young modulus E is the ratio of stress to strain in the linear region of a force-extension or stress-strain graph.

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应力是单位横截面积上的力，单位为 Pa。应变是长度变化的比例，无单位。杨氏模量 E 是力-伸长图或应力-应变图线性区域内应力与应变的比值。

a force-extension graph gives the energy stored elastically. For a material obeying Hooke's law, E_el ows elastic deformation followed by the elastic limit, yield point, plastic deformation, and fracture.

力-伸长图下的面积表示弹性势能。对于遵守胡克定律的材料，E_el = ½ F x = ½ k x²。应力-应变图显示弹性形变、弹性极限、屈服点、塑性形变和断裂。

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6. Waves and Superposition | 波动与叠加

ength λ, frequency f, period T, and speed v. They are related by v = f λ, where f = 1 / T.

波传递能量而不传递物质。关键波量包括波长 λ、频率 f、周期 T 和波速 v。它们的关系为 v = f λ，其中 f = 1 / T。

v = f λ

f = 1 / T

Transverse waves have oscillations perpendicular to the direction of energy transfer, such as light. Longitudinal waves have oscillations parallel to the direction of energy transfer, such as sound. Polarisation can only occur for transverse waves.

横波的振动方向垂直于能量传递方向，例如光。纵波的振动方向平行于能量传递方向，例如声。只有横波才能发生偏振。

The principle of superposition states that when two waves meet, the resultant displacement is the vector sum of their individual displacements. Constructive interference gives a larger amplitude; destructive interference gives a smaller amplitude. Stationary waves form when two identical waves travel in opposite directions; nodes have zero amplitude and antinodes have maximum amplitude.

叠加原理指出，两列波相遇时，合位移等于各自位移的矢量和。相长干涉给出更大振幅；相消干涉给出更小振幅。两列相同波相向传播时形成驻波；波节振幅为零，波腹振幅最大。

length. Interference patterns from two coherent sources can be used to determine wavelength, for example in Young's double-slit experiment using λ = a x / D.

衍射是波通过狭缝或绕过障碍物时的扩散现象。当狭缝尺寸与波长相当时最明显。两个相干光源的干涉图样可用于测定波长，例如杨氏双缝实验中用 λ = a x / D。

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7. Optics: Refraction and Total Internal Reflection | 光学：折射与全内反射

s n = c / v, where c is the speed of light in a vacuum and v is the speed in the material.

波在边界处速度改变时发生折射，导致方向改变。材料折射率 n 定义为 n = c / v，其中 c 为真空中的光速，v 为材料中的光速。

n = c / v

n₁ sin θ₁ = n₂ sin θ₂

sin C = 1 / n

Snell's law relates the angles of incidence and refraction to the refractive indices of the two media. When light travels from a denser to a less dense medium, the angle of refraction is greater than the angle of incidence.

斯涅尔定律将入射角、折射角与两种介质的折射率联系起来。当光从光密介质射向光疏介质时，折射角大于入射角。

If the angle of incidence exceeds the critical angle C, total internal reflection occurs. This requires light to travel from a higher refractive index to a lower refractive index. Total internal reflection is used in optical fibres and prisms, producing bright, sharp images with little energy loss.

若入射角超过临界角 C，则发生全内反射。这要求光从较高折射率介质射向较低折射率介质。全内反射用于光纤和棱镜，能产生明亮、清晰且能量损失小的图像。

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8. Electricity: Current, Resistance and EMF | 电学：电流、电阻与电动势

wo points is the work done per unit charge: V = W / Q. Resistance is defined by R = V / I.

电流是电荷流动的速率：I = ΔQ / Δt。两点间电势差是单位电荷所做的功：V = W / Q。电阻定义为 R = V / I。

I = ΔQ / Δt

V = W / Q

R = V / I

ρ = R A / L

Resistivity ρ is a property of the material, while resistance depends on the material, length, and cross-sectional area. Ohm's law states that current is proportional to potential difference for a conductor at constant temperature. Thermistors and light-dependent resistors do not obey Ohm's law.

电阻率 ρ 是材料的属性，而电阻取决于材料、长度和横截面积。欧姆定律指出，在恒温下导体的电流与电势差成正比。热敏电阻和光敏电阻不遵守欧姆定律。

a drop in terminal potential difference when current flows: ε = I (R + r) and V = ε - I r.

电源的电动势 ε 是单位电荷从其他形式转化为电能所获得的能量。内阻 r 导致电流流过时端电压下降：ε = I (R + r)，V = ε - I r。

ε = I (R + r)

V = ε - I r

P = V I = I² R = V² / R

In series circuits, current is the same through each component and resistances add. In parallel circuits, potential difference is the same across each branch and the reciprocal of total resistance is the sum of reciprocals. Electrical power is the rate of energy transfer.

串联电路中，各元件电流相同，电阻相加。并联电路中，各支路电势差相同，总电阻的倒数等于各电阻倒数之和。电功率是能量传递的速率。

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9. Quantum and Particle Physics | 量子与粒子物理

/ λ, where h is the Planck constant. This equation is central to the photoelectric effect.

光子能量与频率成正比：E = h f = h c / λ，其中 h 为普朗克常数。该方程是光电效应的核心。

E = h f = h c / λ

h f = φ + E_k(max)

λ = h / p

In the photoelectric effect, electrons are emitted from a metal surface when light of frequency above the threshold frequency is incident on it. The work function φ is the minimum energy needed to remove an electron from the surface. The maximum kinetic energy of emitted electrons is h f - φ.

在光电效应中，当频率高于截止频率的光照射金属表面时，会有电子逸出。逸出功 φ 是从表面移出一个电子所需的最小能量。逸出电子的最大动能为 h f - φ。

rovides evidence for wave-particle duality. In atoms, electrons occupy discrete energy levels; photons are emitted or absorbed when electrons transition between levels.

德布罗意提出粒子具有波动性，波长 λ = h / p。电子衍射为波粒二象性提供了证据。原子中电子占据分立能级；电子在能级间跃迁时吸收或发射光子。

Particle physics classifies matter into quarks and leptons. Protons and neutrons are baryons made of three quarks; mesons

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