High-Frequency Exam Topics in IB & WJEC Physics | IB 与 WJEC 物理高频考点总结

📚 High-Frequency Exam Topics in IB & WJEC Physics | IB 与 WJEC 物理高频考点总结

Both IB Physics and WJEC A-level Physics are built on the same core of fundamental principles, and those principles reappear in paper after paper. This article summarises the high-frequency topics that students must master, covering mechanics, waves, electricity, thermal physics and modern physics, with a deliberate emphasis on the equations and concepts that examiners test most often. Each section pairs the physics you must know with the question styles you are likely to meet, so that revision becomes targeted rather than random. By consolidating these key areas you can streamline your revision and boost confidence for both internal assessments and final exams.

IB 物理与 WJEC A-level 物理共享一套基础原理，这些原理在考试中反复出现。本文总结了学生必须掌握的高频考点，涵盖力学、波动、电学、热物理和近代物理，并着重于最常考到的公式和概念。每一节都把必须掌握的物理内容与常见题型配对呈现，让复习变得有的放矢，而不是漫无目的地刷题。通过整合这些关键领域，你可以精简复习、增强信心，从容应对内部评估和最终考试。

1. Kinematics (Motion) | 运动学

The SUVAT equations form the backbone of kinematics, linking displacement (s), initial velocity (u), final velocity (v), acceleration (a) and time (t). Both IB and WJEC papers frequently require applying these equations to linear motion problems, and you must be able to select the correct equation based on the known and unknown variables. In most questions three of the five quantities are given, so the first habit to build is listing s, u, v, a and t before touching the formula booklet. Graphical kinematics is equally examinable: the gradient of a velocity-time graph is acceleration and the area beneath it is displacement.

SUVAT 方程是运动学的核心，联系了位移 (s)、初速度 (u)、末速度 (v)、加速度 (a) 和时间 (t)。IB 和 WJEC 的试题经常要求运用这些方程解决直线运动问题，你必须能够根据已知和未知变量选择合适的方程。多数题目会给出五个量中的三个，因此第一个要养成的习惯就是先列出 s、u、v、a、t，再去翻公式表。图像类运动学同样高频：速度-时间图像的斜率是加速度，图线下方的面积是位移。

v = u + at

s = ut + ½at²

v² = u² + 2as

s = ½(u + v)t

• Always state your positive direction before substituting numbers; a deceleration is a negative acceleration.
• Projectile motion is two independent one-dimensional problems: horizontal acceleration is zero, vertical acceleration is −g.
• question states otherwise, and assume air resistance is negligible unless told otherwise.
• For HL and extension questions, be ready to sketch graphs and interpret gradients and areas.

• 代入数值前先规定正方向；减速对应负加速度。
• 抛体运动是两个独立的一维问题：水平方向加速度为零，竖直方向加速度为 −g。
• 除题目另行说明，取 g = 9.81 m s⁻²，并默认空气阻力可忽略。
• HL 与拓展题要能够画图，并解读斜率与面积的物理意义。

2. Forces and Newton's Laws | 力与牛顿定律

Newton' ant force; the second law quantifies that resultant as F = ma; the third law reminds you that forces always occur in pairs acting on different bodies. Examiners repeatedly ask for free-body diagrams, and marks are awarded for correctly labelled arrows whose lengths reflect relative magnitudes. You should also be fluent with friction (F ≤ μN on a horizontal surface), tension in connected masses, and motion on an inclined plane where the weight component along the slope is mg sin θ.

牛顿三大定律是全部力学题目的基础。第一定律指出，物体在没有合外力作用时保持静止或匀速直线运动；第二定律把这个合力量化为 F = ma；第三定律提醒你，力总是成对出现，且作用在不同物体上。考官反复要求画受力分析图，判断标准是箭头标注正确、长度体现相对大小。你还需要熟练掌握摩擦力（水平面上 F ≤ μN）、连接体中的张力，以及斜面上的运动——沿斜面方向的重力分量为 mg sin θ。

F_net = ma   W = mg   F ≤ μN

• Weight always acts vertically downwards; normal contact force is always perpendicular to the surface.
• For connected bodies, treat the system as a whole to find acceleration, then isolate one mass to find the tension.
• Terminal velocity questions are common: at terminal velocity the resultant force is zero and acceleration is zero.
• Distinguish clearly between mass (kg, a scalar) and weight (N, a vector).

• 重力永远竖直向下；接触面的支持力永远垂直于接触面。
• 处理连接体时，先整体求加速度，再隔离其中一个物体求绳子张力。
• 终速问题很常见：达到终速时合外力为零，加速度为零。
• 务必区分质量（kg，标量）与重量（N，矢量）。

3. Momentum, Impulse and Collisions | 动量、冲量与碰撞

Linear momentum is the product of mass and velocity, and it is conserved in any system where the net external force is zero. Impulse is the product of force and the time for which it acts, and it equals the change in momentum. WJEC and IB both love questions on crumple zones and airbags precisely because they let you link a large change in momentum spread over a longer time to a smaller average force. Collision questions require you to state a direction as positive, then apply conservation of momentum in that direction and decide from the kinetic energy check whether the collision is elastic or inelastic.

动量的定义是质量与速度的乘积；只要系统所受合外力为零，动量就守恒。冲量是力与作用时间的乘积，等于动量的变化量。WJEC 与 IB 都偏爱汽车溃缩区和安全气囊的题目，正是因为它们能让你把「较大的动量变化分摊到更长时间」与「更小的平均作用力」联系起来。碰撞题要求你规定正方向，在该方向上应用动量守恒，再用动能是否守恒来判断碰撞是弹性还是非弹性。

p = mv   F Δt = Δp   m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂

• Impulse is the area under a force-time graph, so graph-reading questions appear frequently.
• Elastic collisions conserve both momentum and kinetic energy; inelastic collisions conserve momentum only.
• Explosions are the reverse case: total momentum before is zero, so the fragments must sum to zero.
• Momentum is a vector, so always resolve into components for two-dimensional problems.

• 冲量等于力-时间图像下的面积，因此读图题出现频率很高。
• 弹性碰撞同时守恒动量与动能；非弹性碰撞只守恒动量。
• 爆炸是反向情形：碰撞前总动量为零，因此碎片动量必须相互抵消。
• 动量是矢量，二维问题必须先分解为分量处理。

4. Work, Energy and Power | 功、能量与功率

. Kinetic energy depends on the square of speed, gravitational potential energy on height, and elastic potential energy on the square of extension. The principle of conservation of energy is the single most useful tool in this topic: in the absence of friction the sum of potential and kinetic energy is constant, and any shortfall is accounted for by work done against resistive forces. Power is the rate of energy transfer, and the relationship P = Fv appears in vehicle and lift questions.

当力使其作用点发生位移时，力就做了功，且只有沿位移方向的分量才贡献功。动能与速度的平方有关，重力势能与高度有关，弹性势能与伸长量的平方有关。能量守恒定律是本专题最有用的工具：无摩擦时势能与动能之和保持不变；若有损耗，则用克服阻力做的功来解释差额。功率是能量转移的速率，关系式 P = Fv 常见于汽车与升降机题目。

W = Fs cos θ   E_k = ½mv²   E_p = mgh   E_elastic = ½kx²

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P = W/t = Fv   efficiency = useful output / total input × 100%

• Work done against gravity is independent of the path taken, because weight is a conservative force.
• Always quote energy answers with units in joules, and check whether a percentage efficiency is required.
• In springs, the area under a force-extension graph gives stored elastic energy.
• Common error: using the total distance instead of the number of cycles when scaling energy in oscillating systems.

• 克服重力做的功与路径无关，因为重力是保守力。
• 能量答案务必写清单位焦耳，并确认题目是否要求给出百分比效率。
• 弹簧问题中，力-伸长量图像下的面积就是储存的弹性势能。
• 常见错误：在振动系统中做能量换算时，用总路程代替周期数。

5. Circular Motion and Gravitation | 圆周运动与万有引力

ecause the direction of velocity changes continuously, there is a centripetal acceleration directed towards the centre, and the resultant force must supply it. Examiners often test this through everyday examples such as a car on a bend, a satellite in orbit, or a mass on a string, and expect you to identify the physical origin of the centripetal force in each case. Gravitational field strength, orbital speed and the relationship T² ∝ r³ follow directly from Newton's law of gravitation.

匀速圆周运动引入角速度，并通过 v = ωr 把线速度与半径联系起来。由于速度方向不断改变，存在指向圆心的向心加速度，必须由合外力提供。考官常用汽车转弯、卫星绕轨、绳系小球等日常情境来考查，并要求你指出每种情境下向心力的物理来源。重力场强度、轨道速率以及 T² ∝ r³ 的关系，都可以直接由万有引力定律导出。

= 2π/T   v = ωr   a = v²/r = ω²r   F = mv²/r

F = GMm/r²   g = GM/r²   T² = 4π²r³ / (GM)

• The centripetal force is never a new force: it is provided by friction, tension, gravity or a normal force.
• Geostationary orbits must have a period of 24 hours, orbit above the equator and rotate in the same sense as the Earth.
• For satellites in orbit, gravitational attraction equals the centripetal requirement, so mass cancels.
• Remember that gravitational field strength and gravitational potential are different quantities, with different units.

• 向心力不是一种新的力：它由摩擦力、张力、重力或支持力提供。
• 地球同步轨道必须周期为 24 小时、位于赤道上方，并与地球自转同向。
• 对在轨卫星，万有引力等于向心力需求，因此质量会被消掉。
• 注意重力场强度与引力势是两个不同的量，单位也不同。

6. Waves and Superposition | 波与叠加

Wave questions open with the relationships between speed, frequency and wavelength, then test superposition, phase difference and path difference. Transverse and longitudinal waves are compared through polarisation and the direction of oscillation relative to the direction of energy transfer. Standing wave questions are extremely common and usually ask you to relate the length of the string or pipe to a whole number of half wavelengths. The boundary conditions matter: a fixed end or a closed pipe forces a node, while a free end or an open pipe forms an antinode.

波动题通常先考查波速、频率与波长的关系，再考查波的叠加、相位差与路程差。横波与纵波的比较围绕偏振以及振动方向与能量传播方向的关系展开。驻波题极其常见，一般要求你把弦或管子的长度与半波长的整数倍联系起来。边界条件很关键：固定端或闭管处必然是波节，自由端或开口端处形成波腹。

v = fλ   phase difference (rad) = 2π × path difference / λ

String 弦 L = nλ/2   Open pipe 开管 L = nλ/2   Closed pipe 闭管 L = (2n − 1)λ/4

• Constructive superposition needs a path difference of nλ; destructive needs (n + ½)λ for coherent sources.
• Polarisation is evidence that light is a transverse wave, and only transverse waves can be polarised.
• Doppler questions use the change in observed frequency; state clearly whether the source is approaching or receding.
• Always use coherent sources when explaining an interference pattern, since a constant phase difference is required.

• 相长叠加需要路程差为 nλ；对相干波源，相消叠加需要 (n + ½)λ。
• 偏振是光为横波的证据，只有横波才能被偏振。
• 多普勒题考查观测频率的变化，必须明确说明波源是在接近还是远离。
• 解释干涉图样时一定要强调相干波源，因为需要恒定的相位差。

7. Refraction, Diffraction and Interference | 折射、衍射与干涉

Refraction questions test Snell's law and the conditions for total internal reflection, which occurs only when light travels from a denser to a less dense medium and the angle of incidence exceeds the critical angle. The two-slit arrangement and the diffraction grating are the classic interference experiments: the fringe spacing depends on wavelength, slit separation and screen distance, while the grating equation gives the angles of the principal maxima. You should be able to explain why a single slit pattern has a central maximum twice as wide as the others, and why increasing the number of slits sharpens the maxima.

折射题考查斯涅尔定律以及全反射的条件——只有光从光密介质射向光疏介质，且入射角大于临界角时才会发生全反射。双缝装置与衍射光栅是经典的干涉实验：条纹间距取决于波长、缝间距与屏距，而光栅方程给出各级主极大的角度。你还应能解释为什么单缝图样的中央亮纹宽度是其他亮纹的两倍，以及为什么增加缝数会使主极大变得更锐利。

nbsp;  sin c = n₂ / n₁   d sin θ = nλ   w = λD / s

• is defined as the ratio of the speed of light in vacuum to that in the medium, so n = c/v.
• Frequency does not change on refraction; speed and wavelength do.
• Diffraction becomes noticeable when the slit width is comparable to the wavelength.
• ating, the maximum observable order is limited by sin θ ≤ 1, a favourite calculation step.

• 折射率定义为真空光速与该介质中光速之比，即 n = c/v。
• 折射时频率不变，改变的是波速与波长。
• 当缝宽与波长可比时，衍射现象才明显。
• 光栅问题中，可观测的最高级次受 sin θ ≤ 1 限制，这是高频计算步骤。

8. Thermal Physics and Ideal Gases | 热学与理想气体

Thermal physics links the macroscopic quantities of pressure, volume and temperature with the microscopic behaviour of molecules. The ideal gas equation appears in two equivalent forms, one using the number of moles and the other the number of molecules. The kinetic theory model rests on clearly stated assumptions: molecules are in random motion, collisions are elastic, the volume of the molecules is negligible, and there are no intermolecular forces except during collisions. From these assumptions the average molecular kinetic energy is directly proportional to the absolute temperature, which explains why the kelvin scale must be used in every gas calculation.

热学把压强、体积、温度等宏观量与分子的微观行为联系起来。理想气体方程有两种等价形式，一种用摩尔数，另一种用分子数。气体动理论建立在明确列出的假设之上：分子做无规则运动、碰撞是弹性的、分子自身体积可忽略、除碰撞瞬间外分子间无相互作用力。由这些假设可推出分子的平均动能与热力学温度成正比，这也解释了为什么所有气体计算都必须使用开尔文温标。

pV = nRT   pV = NkT   T(K) = θ(°C) + 273.15

Q = mcΔT   Q = mL   average E_k = 3/2 kT

• Internal energy is the sum of the randomly distributed kinetic and potential energies of the particles.
• During a change of state the temperature stays constant, so all the energy supplied goes into breaking bonds.
• In the first law of thermodynamics, quote your sign convention explicitly, since it differs between syllabuses.
• Pressure on the container walls arises
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