📚 Year 7 Cambridge Physics: Key Concepts and Common Mistakes | 剑桥 Year 7 物理高频考点与易错题分析
Year 7 Cambridge Physics covers essential topics including forces, energy, waves, electricity and the Earth in space. This article highlights the most frequently assessed concepts and the mistakes students commonly make, helping to sharpen your understanding and avoid losing unnecessary marks.
剑桥 Year 7 物理涵盖力、能量、波、电学以及地球与太空等核心主题。本文聚焦最高频的考点和学生们最容易出错的题目，帮助你加深理解并避免不必要的失分。
1. Speed and Motion Graphs | 速度与运动图像
Speed is the distance travelled per unit time. The key formula is speed equals distance divided by time. You must be able to rearrange it and use the correct units, such as metres per second (m s⁻¹) or kilometres per hour (km h⁻¹).
速度是单位时间内移动的距离。核心公式为速度等于距离除以时间。你必须能够变换公式并使用正确的单位，如米每秒 (m s⁻¹) 或千米每小时 (km h⁻¹)。
speed = distance ÷ time
A common error is mixing up distance–time graphs: a horizontal line means the object is stationary, not moving slowly. The slope (gradient) tells you the speed; a steeper line indicates a higher speed.
常见的错误是混淆距离-时间图像：水平线表示物体静止，而不是移动得慢。斜率（梯度）代表了速度；线越陡表示速度越大。
Another typical mistake is converting units incorrectly. For example, to change km h⁻¹ to m s⁻¹, you divide by 3.6. Many students forget to convert minutes to seconds before calculating average speed.
另一个典型错误是单位换算不对。例如，将 km h⁻¹ 换算成 m s⁻¹ 需要除以 3.6。很多学生在计算平均速度前会忘记把分钟换算为秒。
2. Forces and Their Effects | 力及其作用效果
A force is a push or a pull, measured in newtons (N). Forces can change an object’s shape, speed or direction. Balanced forces keep an object at rest or moving at constant speed; unbalanced forces cause acceleration or deceleration.
力是一种推或拉，单位为牛顿 (N)。力可以改变物体的形状、速度或方向。平衡力使物体保持静止或匀速运动；非平衡力则会导致加速或减速。
A very frequent exam pitfall is confusing mass (measured in kilograms) with weight (measured in newtons). Weight is the gravitational force on a mass, given by W = m × g, where g is about 10 N/kg on Earth.
一个高频的考试易错点是混淆质量（单位为千克）与重量（单位为牛顿）。重量是作用在物体上的重力，公式为 W = m × g，地球上 g 约为 10 N/kg。
W = m × g
Students often think that if an object is moving, there must be a resultant force acting on it. In reality, an object moving at constant speed in a straight line has balanced forces.
学生常误以为只要物体在运动，就一定受到合力作用。实际上，沿直线匀速运动的物体所受的力是平衡的。
3. Energy Forms and Transfers | 能量形式与转化
Energy exists in different forms: kinetic, gravitational potential (GPE), chemical, thermal (heat), electrical, light, sound and elastic potential. The conservation of energy states that energy cannot be created or destroyed, only transferred or converted.
能量存在多种形式：动能、重力势能 (GPE)、化学能、热能、电能、光能、声能和弹性势能。能量守恒定律指出，能量既不能被创造也不能被消灭，只能被转移或转化。
Kinetic energy (Eₖ) depends on mass and speed, while gravitational potential energy (Eₚ) depends on mass, height and gravitational field strength. The formula Eₚ = m × g × h is often tested, but Year 7 calculations are usually kept simple.
动能 (Eₖ) 依赖于质量和速度，而重力势能 (Eₚ) 则依赖于质量、高度和引力场强度。公式 Eₚ = m × g × h 常被考查，但 Year 7 的计算通常会简化。
Eₚ = m × g × h
An error many students make is saying energy is ‘used up’ when a device operates. Instead, describe how energy is converted from one form to another, such as electrical energy turning into light and heat in a bulb.
许多学生犯的一个错误是说电器工作时能量被“用光了”。应该描述能量如何从一种形式转化为另一种形式，比如在灯泡中电能转化为光能和热能。
Energy transfer diagrams or Sankey diagrams often appear in exams. Make sure you label the useful and wasted energies correctly and remember that the total input equals total output.
考试中经常出现能量转移图或桑基图。务必正确标出有用的和浪费的能量，并牢记总输入能量等于总输出能量。
4. Sound Waves | 声波
Sound is produced by vibrating objects and travels as longitudinal waves. It requires a medium (solid, liquid or gas) to travel, so sound cannot be heard in a vacuum. The speed of sound in air is about 340 m/s.
声音由振动的物体产生，并以纵波的形式传播。它需要介质（固体、液体或气体）才能传播，因此真空中听不到声音。声音在空气中的速度约为 340 m/s。
The amplitude of a sound wave determines its loudness, while the frequency determines the pitch. A high frequency, short wavelength wave sounds high-pitched. Many students mistakenly think a taller wave always means a higher pitch.
声波的振幅决定了响度，而频率决定了音调。高频、短波长的声音听起来音调高。很多学生误以为更高的波形总意味着更高的音调。
On wave diagrams, count the number of complete waves per second to find frequency. Something often missed is that sound travels fastest in solids, slower in liquids and slowest in gases, not the other way round.
在波形图中，通过数每秒完整波的个数来找到频率。另一个常被忽略的点是声音在固体中传播最快，液体中次之，气体中最慢，而不是反过来。
5. Light: Reflection and Refraction | 光的反射与折射
The law of reflection states that the angle of incidence equals the angle of reflection, both measured from the normal line. A plane mirror forms a virtual, upright, laterally inverted image that is the same size as the object and located as far behind the mirror as the object is in front.
反射定律指出入射角等于反射角，两者都从法线量起。平面镜成虚像、正立、左右颠倒，并且像与物大小相等，像到镜面的距离等于物到镜面的距离。
Refraction occurs when light passes from one medium to another at an angle, causing a change in speed and direction. Light bends towards the normal when entering a denser medium, and away from the normal when entering a less dense medium.
当光以一定角度从一种介质进入另一种介质时会发生折射，导致速度和方向的改变。光进入密度较大的介质时偏向法线，进入密度较小的介质时偏离法线。
Common mistakes include drawing reflected rays on the wrong side of the normal or forgetting that the angle of refraction is measured from the normal too. Make sure your ray diagrams have arrows showing the correct direction of light travel.
常见错误包括把反射光线画在了法线的错误一侧，或者忘记折射角也是从法线量起。务必在你的光线图中用箭头标出光的正确传播方向。
6. Simple Circuits | 简单电路
A basic circuit must include a power source, connecting wires and a component such as a bulb, buzzer or motor. Drawing the correct circuit symbols is essential. Series circuits provide a single path for the current; if one component breaks, the whole circuit stops working.
一个基本电路必须包括电源、导线和像灯泡、蜂鸣器或电动机这样的元件。画出正确的电路符号至关重要。串联电路为电流提供单一路径；如果一个元件损坏，整个电路就会停止工作。
In a series circuit, the current is the same everywhere, but the voltage is shared. In a parallel circuit, the voltage across each branch is the same, while the current splits. Students often wrongly think current gets ‘used up’ around a circuit.
在串联电路中，各处电流相同，但电压被分配。在并联电路中，各支路两端电压相同，而电流分流。学生常错误地认为电流在电路中会被“消耗掉”。
A short circuit is a low-resistance path that allows current to bypass a component, which can cause overheating. In exams, always check if this is the reason a bulb does not light up.
短路是一条低电阻路径，让电流绕过元件，这可能导致过热。考试中，一定要检查这是否为灯泡不发亮的原因。
7. Magnets and Magnetic Fields | 磁与磁场
Magnets have a north pole and a south pole. Like poles repel, unlike poles attract. Magnetic field lines run from north to south outside the magnet and from south to north inside. The stronger the field, the closer the lines.
磁铁有北极和南极。同名磁极相互排斥，异名磁极相互吸引。磁力线在磁铁外部从北极指向南极，在磁铁内部则从南极指向北极。磁场越强，磁力线越密。
Only magnetic materials such as iron, nickel and cobalt are attracted to magnets; not all metals are magnetic. A piece of steel can be magnetised to make a permanent magnet, while iron is easy to magnetise but loses its magnetism quickly – useful for electromagnets.
只有铁、镍、钴等磁性材料才会被磁铁吸引；并非所有金属都有磁性。钢可以被磁化制成永磁体，而铁虽然容易磁化但也容易失去磁性——这对电磁铁很有用。
Misconceptions arise when students think all metals are magnetic or that bigger magnets are always stronger. Also, remember the Earth has a magnetic field: the geographic North Pole is near a magnetic south pole, which is why a compass north needle points roughly north.
误区包括学生认为所有金属都有磁性，或者更大的磁铁总是更强。此外，记住地球也有磁场：地理北极附近是地磁南极，这就是为什么指南针的北极大致指向北方。
8. The Solar System and Earth’s Motion | 太阳系与地球运动
The order of the planets from the Sun is: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. The Earth rotates on its axis once every 24 hours, giving day and night. It revolves around the Sun once a year, but seasons are caused by the tilt of Earth’s axis, not by the distance from the Sun.
行星距太阳由近及远的顺序为：水星、金星、地球、火星、木星、土星、天王星和海王星。地球每 24 小时自转一周，形成昼夜。地球每年绕太阳公转一周，但季节是由地轴的倾斜造成的，而不是由距太阳的远近造成的。
A frequent exam trap is saying that summer occurs because Earth is closer to the Sun. The correct explanation is that the hemisphere tilted towards the Sun receives more direct sunlight and longer daylight hours.
考试中常见的一个陷阱是说夏天是因为地球离太阳更近。正确的解释是朝向太阳的那个半球获得了更直接的阳光和更长的白昼时长。
Moon phases are caused by the changing relative positions of the Earth, Moon and Sun. The Moon does not produce its own light; it reflects sunlight. Remember to describe a full moon as when the Moon is on the opposite side of Earth from the Sun.
月相是由地球、月球和太阳相对位置的变化引起的。月球本身不发光，它反射太阳光。要记住满月时月球处于地球背向太阳的一侧。
9. Common Pitfalls and Exam Technique | 常见失分点与考试技巧
Always write the correct units with numerical answers. Missing units or using the wrong ones (e.g. m/s for force) can lose marks. In ‘explain’ or ‘describe’ questions, use scientific keywords such as ‘vibration’, ‘amplitude’, ‘resultant force’ and ‘virtual image’.
数字答案始终要写上正确的单位。遗漏单位或使用错误单位（如用力表示成 m/s）会丢失分数。在“解释”或“描述”类题目中，使用科学关键词，如“振动”、“振幅”、“合力”和“虚像”。
Draw diagrams clearly with a sharp pencil and a ruler. Label all arrows, normals and forces precisely. When plotting graphs, choose a suitable scale, plot points carefully and label axes with quantity and unit.
作图要用削尖的铅笔和直尺画清楚。精确标出所有箭头、法线和力。绘制图像时，选择合适的比例尺，仔细描点，并在坐标轴上标出物理量和单位。
Read the question carefully: a question about ‘speed’ is different from one about ‘velocity’. Check if you need to calculate average speed or instantaneous speed. Practise rearranging the speed equation so you can quickly switch between distance, time and speed.
仔细审题：关于“速率”的题目与关于“速度”的题目不同。检查是需要计算平均速率还是瞬时速率。多练习变换速度公式，以便能在距离、时间和速度间迅速转换。
Finally, manage your time well in exams. Attempt easier questions first to build confidence, and always leave a few minutes to check for careless errors like missing units or misread values.
最后，考试中要合理分配时间。先做简单的题目建立信心，并始终留出几分钟检查粗心错误，如漏写单位或看错数据。
Published by TutorHao | Physics Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导