📚 Year 10 Cambridge Physics: High-Frequency Exam Topics and Common Mistakes | Year 10 Cambridge 物理：高频考点与易错题分析
Welcome to this revision guide covering the most frequently tested topics in Year 10 Cambridge IGCSE Physics, along with the mistakes students make time and again. Each section focuses on a critical concept, explains common pitfalls and shows you how to avoid losing marks in your exams. Make sure you understand the reasoning behind every formula and graph – simply memorising will not be enough.
欢迎阅读这篇针对 Year 10 Cambridge IGCSE 物理高频考点与常见错误的复习指南。每个小节都聚焦一个关键概念，解析学生反复出现的问题，并告诉你如何避免在考试中失分。请务必理解每个公式和图像背后的原理——单纯死记硬背是不够的。
1. Speed-Time and Distance-Time Graphs | 速度-时间图与距离-时间图
In a distance-time graph, the gradient represents speed. A straight line means constant speed; a horizontal line means the object is stationary. In a speed-time graph, the gradient gives acceleration, and the area under the graph represents the distance travelled. Many students wrongly use the gradient of a distance-time graph to calculate acceleration, or they confuse the area under a speed-time graph with displacement rather than distance.
在距离-时间图中，斜率表示速度。直线意味着匀速，水平线表示物体静止。在速度-时间图中，斜率代表加速度，图线下的面积代表所经过的距离。很多学生错误地用距离-时间图的斜率计算加速度，或者将速度-时间图下的面积误解为位移而非路程。
A common numerical error is forgetting to convert minutes to seconds or km/h to m/s. Always express time in seconds and distance in metres before calculating speed or acceleration. For uniform acceleration, use v = u + a t and s = u t + ½ a t², where u is initial velocity, v is final velocity, a is acceleration and t is time.
常见的计算错误是忘记将分钟转换为秒，或将 km/h 转换为 m/s。在计算速度或加速度之前，一定要把时间化为秒、距离化为米。对于匀加速运动，使用 v = u + a t 和 s = u t + ½ a t²，其中 u 是初速度，v 是末速度，a 是加速度，t 是时间。
2. Newton's Laws and Resultant Force | 牛顿定律与合力
Many questions give several forces acting on an object and ask for the resultant force. If forces act in the same direction, add them; if they act in opposite directions, subtract. The direction of the resultant force determines the direction of acceleration. The second law, F = m a, links resultant force (N), mass (kg) and acceleration (m/s²). Always use mass in kilograms – a common mistake is to use weight (in newtons) as mass.
很多题目会给出作用在物体上的几个力，要求计算合力。如果力的方向相同就相加，方向相反则相减。合力的方向决定加速度的方向。牛顿第二定律 F = m a 将合力（N）、质量（kg）和加速度（m/s²）联系起来。务必使用千克作为质量单位——一个常见错误是把重力（以牛顿为单位）当作质量代入公式。
Also, students often ignore frictional forces when calculating the net force acting on a moving object. In exam problems, look for terms like 'constant speed' – when speed is constant, the resultant force is zero. This is a direct application of Newton's first law.
此外，学生在计算运动物体的合力时常常忽略摩擦力。在考题中，看到“匀速”一词就要注意：当速度恒定时，合力为零。这是牛顿第一定律的直接应用。
3. Momentum and Conservation | 动量及守恒
Momentum is a vector quantity: p = m v. In a closed system, total momentum before a collision or explosion equals total momentum afterwards. A frequent mistake is forgetting that momentum has direction – when objects move in opposite directions, you must assign positive and negative signs. Another error is adding the masses incorrectly when objects stick together.
动量是矢量：p = m v。在封闭系统中，碰撞或爆炸前的总动量等于之后的总动量。常见的错误是忘记动量具有方向性——当物体朝相反方向运动时，必须赋予正负号。另一个错误是当物体粘在一起时，质量相加的方式不对。
In exam calculations, sketch a 'before' and 'after' : total initial momentum = total final momentum. Then solve. Always state the unit kg m/s.
在考试计算中，画出“之前”和“之后”的示意图，标出速度及其方向，写出守恒方程：总初动量 = 总末动量。然后求解。始终要写出单位 kg m/s。
4. Energy Transfers and Work Done | 能量转换与做功
Work is done when a force moves an object: W = F d ion of the force). Energy can be transferred between stores: kinetic, gravitational potential, thermal, chemical, etc. For a falling object, gravitational potential energy (GPE) is converted to kinetic energy (KE). A typical error is applying m g h = ½ m v² but forgetting that some energy is lost to air resistance or friction.
当力使物体移动时就做了功：W = F d（力 × 沿力方向移动的距离）。能量可以在不同储存间转移：动能、重力势能、热能、化学能等。对于下落的物体，重力势能（GPE）转化为动能（KE）。一个典型错误是套用 m g h = ½ m v² 却忘记部分能量会因空气阻力或摩擦而损耗。
t energy / total input energy, often expressed as a percentage. Students sometimes mix up the input and output values. Always write the formula and identify the 'useful' energy in the context of the question.
效率的计算也容易出现失误。效率 = 有用输出能量 / 总输入能量，通常以百分比表示。学生有时会混淆输入值和输出值。务必先写出公式，再结合题目情境确定哪个是“有用”的能量。
5. Pressure in Solids, Liquids and Gases | 固体、液体和气体的压强
For solids, pressure is force per unit area: p = F / A. The unit is pascal (Pa) or N/m². When calculating pressure exerted by a block on a surface, use the area of the face in contact. A common error is using the wrong area (e.g. using total surface area instead of contact area).
对于固体，压强等于单位面积上的力：p = F / A。单位是帕斯卡（Pa）或 N/m²。在计算一个物块对表面的压强时，要使用接触面的面积。常见错误是用错了面积（例如用总表面积代替接触面积）。
In a liquid, pressure depends on depth, density and gravitational field strength: p = h ρ g. Students often forget that this formula gives the pressure due to the liquid alone; atmospheric pressure may also act on the surface. Gas pressure is explained by particles colliding with the walls – change in momentum of many particles leads to a steady force.
在液体中，压强与深度、密度和重力场强度有关：p = h ρ g。学生常常忘记这个公式仅给出由液体产生的压强；大气压强可能还作用在液面上。气体压强可用粒子碰撞器壁来解释——大量粒子动量变化的结果产生了持续的力。
6. Thermal Physics: Specific Heat Capacity | 热学：比热容
The energy needed to raise the temperature of a substance is given by Q = m c Δθ rature change. For example, if water is heated from 20 °C to 80 °C, Δθ = 60 °C, not 80 °C.
提高物质温度所需的能量由 Q = m c Δθ 给出，其中 Δθ 是温度变化量。一个极其常见的错误是代入物体温度本身，而不是温度变化量。例如，水从 20 °C 加热到 80 °C，Δθ = 60 °C，而不是 80 °C。
ng melting or boiling, the temperature stays constant even though energy is being supplied – misread the graph and attempt to use Q = m c Δθ during a phase change, which is incorrect.
在涉及加热或冷却曲线的题目中，必须识别出发生物态变化的平坦区域。在熔化或沸腾过程中，尽管能量不断输入，温度却保持不变——这部分能量用于打破分子间的作用力，而不是增加动能。学生经常误读图像，在相变阶段试图使用 Q = m c Δθ，这是不正确的。
7. Wave Properties: v = f λ | 波的性质：波速公式
The wave equation links speed (v), frequency (f) and wavelength (λ): v = f λ tz, Hz); period T = 1/f is the time for one wave. Another frequent mistake is mixing units – in m/s, wavelength in metres, frequency in Hz. If wavelength is given in cm, convert to m.
波速公式将波速（v）、频率（f）和波长（λ）联系起来：v = f λ。学生常混淆频率和周期。频率是每秒完整波的个数（赫兹，Hz）；周期 T = 1/f 是一个波所需的时间。另一个常见错误是单位混用——速度用 m/s，波长用米，频率用 Hz。如果波长以 cm 给出，要换算成 m。
When interpreting oscilloscope traces or displacement–time graphs, be careful to measure the time period correctly from the grid. Many candidates count half a cycle as a full cycle. For a transverse wave, the amplitude is the maximum displacement from the rest position, not the distance from peak to trough.
在分析示波器波形或位移-时间图像时，要从网格上正确测量周期。很多考生把半个周期误数成一个完整周期。对于横波，振幅是偏离平衡位置的最大位移，而不是从波峰到波谷的垂直距离。
8. Electromagnetic Spectrum | 电磁波谱
The electromagnetic spectrum, in order of increasing frequency (decreasing wavelength), runs: radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays. All travel at the same speed in a vacuum (c = 3.0 × 10⁸ m/s). A typical mistake is placing infrared next to gamma rays or forgetting that visible light is only a tiny part of the spectrum.
电磁波谱按频率递增（波长递减）的顺序排列为：无线电波、微波、红外线、可见光、紫外线、X 射线、伽马射线。所有电磁波在真空中的速度相同（c = 3.0 × 10⁸ m/s）。一个典型错误是把红外线排在伽马射线旁边，或者忘记可见光只是电磁波谱中极小的一部分。
Exam questions often ask for applications or dangers of specific regions. For instance, microwaves are used for satellite communication and cooking; infrared for thermal imaging; ultraviolet can cause skin cancer; X-rays for medical imaging but can damage cells. Students frequently mix up the uses of X-rays and gamma rays, or wrongly assign heating effect to ultraviolet instead of infrared.
考题常要求写出特定波段的用途或危害。例如，微波用于卫星通信和烹饪；红外线用于热成像；紫外线可导致皮肤癌；X 射线用于医学成像但可能损伤细胞。学生们经常混淆 X 射线和伽马射线的用途，或者错误地把热效应归于紫外线而不是红外线。
9. Electric Circuits and Ohm's Law | 电路与欧姆定律
Ohm's law states V = I R for a conductor at constant temperature. The resistance of a fixed resistor is constant; for a filament lamp, resistance increases with temperature because the metal ions vibrate more, making it harder for electrons to flow. A common error is to treat all components as ohmic and assume resistance never changes.
欧姆定律指出，在温度不变的条件下，对导体有 V = I R。固定电阻器的电阻是恒定的；而白炽灯的电阻随温度升高而增大，因为金属离子振动加剧，阻碍电子流动。一个常见错误是把所有元件都当作欧姆元件处理，认为电阻永远不会变化。
In series circuits, current is the same everywhere, and the total resistance is the sum of individual resistances. In parallel circuits, the potential difference across each branch is the same, and the total resistance is less than the smallest individual resistance. Many students add parallel resistances as if they were in series. Remember: 1/Rₜ = 1/R₁ + 1/R₂ + ... for parallel.
在串联电路中，各处电流相等，总电阻是各电阻之和。在并联电路中，各支路两端的电压相同，总电阻小于最小的单个电阻。许多学生把并联电阻当作串联来计算。请记住：并联时 1/Rₜ = 1/R₁ + 1/R₂ + ...
10. Electrical Power and Energy | 电功率与电能
Power is the rate of energy transfer: P = I V, also expressed as P = I² R or P = V² / R rage power formulas incorrectly, or they use P = I V for non-ohmic components without checking whether it's appropriate.
功率是能量传递的速率：P = I V，对于电阻性元件也可表示为 P = I² R 或 P = V² / R。一个非常常见的错误是选错 P、I、V、R 的组合。例如，学生把均方根值错误地代入平均功率公式，或者对非欧姆元件不加判断地使用 P = I V。
For energy consumption, E = P t ting the cost of electricity, energy is usually measured in kilowatt-hours (kWh). Students often forget to convert watts to kilowatts and minutes to hours. A typical error is using 60 W for one minute and calculating energy as 60 kWh, instead of converting 60 W to 0.060 kW and 1 minute to 1/60 hour, giving 0.001 kWh.
对于消耗的电能，E = P t（能量 = 功率 × 时间）。在计算电费时，能量常以千瓦时（kWh）为单位。学生往往忘记将瓦特转换为千瓦、分钟转换为小时。一个典型错误是：将 60 W 的电器运行 1 分钟，算出的能量直接当成 60 kWh，而正确的做法是先将 60 W 化为 0.060 kW、1 分钟化为 1/60 小时，得到 0.001 kWh。
11. Radioactive Decay and Half-Life | 放射性衰变与半衰期
Half-life is the time taken for half the radioactive nuclei in a sample to decay. It is constant for a given isotope. A common mistake is to think that after two half-lives all the substance has decayed – in fact, one quarter remains. Another error is misreading the decay curve by drawing the half-life incorrectly. Always pick a convenient starting count rate on the y-axis, halve it, read the time, and check that the same time interval halves the count rate again.
半衰期是样品中一半放射性原子核发生衰变所需的时间，对给定的同位素是常数。一个常见错误是认为经过两个半衰期后所有物质都已衰变——实际上，剩余四分之一。另一个错误是从衰变曲线上错误地读取半衰期。始终在 y 轴上选取一个方便的初始计数率，将其减半，读出对应的时间，然后验证经过同样的时间间隔后计数率是否再次减半。
Nuclear equations must balance the total mass numbers and total atomic numbers. In alpha decay, the nucleus loses 2 protons and 2 neutrons (⁴₂He nucleus); in beta decay, a neutron turns into a proton and emits an electron (⁰₋₁e). Students often forget to balance the atomic numbers, leading to wrong element symbols.
核方程必须保证总质量数和总原子序数相等。α 衰变中，原子核失去 2 个质子和 2 个中子（⁴₂He 核）；β 衰变中，一个中子转变成质子并放出一个电子（⁰₋₁e）。学生经常忘记平衡原子序数，导致写错元素符号。
12. Scalars and Vectors: Common Confusions | 标量与矢量：常见混淆
Scalars have magnitude only; vectors have both magnitude and direction. Distance is scalar, displacement is vector; speed is scalar, velocity is vector. A tricky situation is when an object moves in a circle at constant speed: its speed is constant, but its velocity is constantly changing because the direction changes. Students often claim the velocity of such an object is zero or constant.
标量只有大小，矢量既有大小又有方向。距离是标量，位移是矢量；速率是标量，速度是矢量。一个容易出错的情形是物体做匀速圆周运动：速率不变，但速度始终在变化，因为方向不断改变。学生经常声称这种物体的速度为零或不变。
Force, momentum, acceleration and weight are all vectors. When combining vectors, you must consider direction. For example, two forces of 5 N and 5 N acting in opposite directions give a resultant of 0 N, not 10 N. Failing to assign positive and negative signs is a regular source of lost marks in resultant force and momentum questions.
力、动量、加速度和重力都是矢量。合成矢量时必须考虑方向。例如，两个 5 N 的力沿相反方向作用，合力为 0 N，而不是 10 N。在合力和动量问题中，漏标正负号是经常丢分的原因。
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