📚 IGCSE WJEC Physics: Clarifying Key Concept Distinctions | IGCSE WJEC 物理：关键概念辨析
In IGCSE Physics, students often confuse terms that sound similar but have distinct meanings. This article clarifies common pairs of concepts found in the WJEC specification, helping you to avoid typical mistakes and strengthen your understanding.
在 IGCSE 物理中，学生经常混淆听起来相似但含义不同的术语。本文澄清了 WJEC 大纲中常见的概念配对，帮助你避免典型错误并加深理解。
1. Speed vs Velocity | 速率与速度
Speed is a scalar quantity that tells you how fast an object is moving, without any regard to direction. It is calculated as the total distance travelled divided by the time taken.
速率是一个标量，它说明物体运动有多快，不考虑方向。它等于行驶的总距离除以所用时间。
speed = distance / time
Velocity, on the other hand, is a vector quantity. It describes both how fast and in which direction an object moves. Velocity is defined as displacement divided by time.
另一方面，速度是一个矢量。它同时描述物体运动的快慢和方向。速度定义为位移除以时间。
velocity = displacement / time
If a runner completes a 400 m lap in 50 seconds, her average speed is 8 m/s. However, because she returns to the starting point, her displacement is zero and her average velocity for the whole lap is 0 m/s.
如果一位跑步者用50秒跑完400米一圈，她的平均速率是8 m/s。但由于她回到了起点，她的位移为零，整个一圈的平均速度为0 m/s。
2. Mass vs Weight | 质量与重量
Mass is a scalar quantity that measures the amount of matter in an object. It does not change with location and is measured in kilograms (kg).
质量是一个标量，衡量物体所含物质的多少。它不随位置改变，以千克（kg）为单位。
Weight is a vector quantity caused by the gravitational attraction on a mass. It always acts towards the centre of the planet and is measured in newtons (N).
重量是一个矢量，由作用在质量上的万有引力引起。它总是指向行星的中心，以牛顿（N）为单位。
weight = mass × gravitational field strength (W = mg)
On Earth, g ≈ 9.8 N/kg, so a 5 kg object has a mass of 5 kg everywhere but a weight of about 49 N on Earth and only about 8 N on the Moon.
在地球上，g ≈ 9.8 N/kg，所以一个5 kg的物体在任何地方质量都是5 kg，但在地球上的重量约为49 N，在月球上仅约8 N。
3. Distance vs Displacement | 距离与位移
Distance is a scalar quantity that refers to the total length of the path travelled by an object. It has no direction and can never decrease for a moving object; it only adds up.
距离是一个标量，指物体运动路径的总长度。它没有方向，对于运动物体来说永远不会减少，只会累积。
Displacement is a vector quantity that measures the straight-line distance from the starting point to the finishing point, together with the direction.
位移是一个矢量，测量从起点到终点的直线距离，连同方向。
Imagine a person walking 3 km east and then 4 km north. The distance travelled is 7 km, but the magnitude of displacement is 5 km northeast (calculated by Pythagoras: √(3² + 4²) = 5 km).
设想一个人向东走3 km，然后向北走4 km。他运动的距离是7 km，但位移的大小是5 km 东北方向（由勾股定理计算：√(3² + 4²) = 5 km）。
4. Heat vs Temperature | 热量与温度
Heat is the transfer of thermal energy from a hotter object to a cooler one. It is measured in joules (J) and depends on mass, specific heat capacity, and temperature change.
热量是热能从较热物体传递到较冷物体的能量。它以焦耳（J）为单位，取决于质量、比热容和温度变化。
Temperature is a measure of the average kinetic energy of the particles in a substance. It does not depend on the mass of the object and is usually measured in degrees Celsius (°C) or kelvin (K).
温度是物质内粒子平均动能的量度。它不依赖于物体的质量，通常以摄氏度（°C）或开尔文（K）为单位。
For example, a small cup of water at 80 °C has a higher temperature than a cold bath at 20 °C, but the bath contains much more internal energy. Adding the same amount of heat will raise the temperature more in the cup than in the bath.
例如，一小杯80 °C的水比20 °C的冷水浴温度更高，但冷水浴含有更多的内能。加入相同的热量，杯子的温升会比浴缸大得多。
5. Power vs Energy | 功率与能量
Energy is the capacity to do work. It exists in many forms (kinetic, potential, thermal, etc.) and is measured in joules (J). The law of conservation of energy states that energy cannot be created or destroyed, only transferred.
能量是做功的能力。它有多种形式（动能、势能、热能等），以焦耳（J）为单位。能量守恒定律指出，能量不能被创造或消灭，只能被转移。
Power is the rate at which energy is transferred or work is done. It is a scalar quantity measured in watts (W), where 1 W = 1 J/s.
功率是能量转移或做功的速率。它是一个标量，以瓦特（W）为单位，1 W = 1 J/s。
power = energy transferred / time or P = E / t
A 60 W light bulb transfers 60 J of electrical energy into heat and light every second. A more powerful 100 W bulb transfers energy at a faster rate, not necessarily using more energy overall unless it is on for the same length of time.
一个60 W的灯泡每秒将60 J的电能转换为热能和光能。一个100 W的更大功率灯泡以更快的速率转移能量，除非点亮相同时间，未必消耗更多总能量。
6. Current vs Voltage | 电流与电压
Electric current is the rate of flow of electric charge. It is measured in amperes (A) and is analogous to the flow of water through a pipe. In a series circuit, the current is the same at all points.
电流是电荷流动的速率。它以安培（A）为单位，类似于水流过管道。在串联电路中，所有位置的电流相同。
Voltage (potential difference) is the energy transferred per unit charge between two points. It is measured in volts (V) and can be thought of as the ‘push’ that drives charges around a circuit.
电压（电势差）是两点之间单位电荷转移的能量。它以伏特（V）为单位，可以理解为驱使电荷绕电路运动的’推力’。
V = W / Q and V = IR (Ohm’s law)
If a resistor has a current of 2 A and a voltage of 6 V across it, its resistance is R = V/I = 3 Ω. The voltage tells us how much energy each coulomb loses, while the current tells us how many coulombs pass per second.
如果电阻器流过2 A的电流，两端电压为6 V，其电阻为R = V/I = 3 Ω。电压告诉我们每库仑失去多少能量，而电流告诉我们每秒通过多少库仑。
7. Series vs Parallel Circuits | 串联电路与并联电路
In a series circuit, components are connected one after another in a single loop. The same current flows through all components, but the total voltage is shared across them.
在串联电路中，元件一个接一个连接成单一回路。相同的电流流过所有元件，但总电压在它们之间分配。
In a parallel circuit, components are connected on separate branches. The voltage across each branch is the same as the source voltage, but the current from the source divides among the branches.
在并联电路中，元件连接在分开的支路上。每个支路上的电压与电源电压相同，但来自电源的电流在各支路间分配。
| Series | Parallel |
| Current: same everywhere (I = I₁ = I₂) | Current: split (I = I₁ + I₂) |
| Voltage: shared (V = V₁ + V₂) | Voltage: same across each branch (V = V₁ = V₂) |
| Resistance: adds up (R_total = R₁ + R₂) | Resistance: decreases (1/R_total = 1/R₁ + 1/R₂) |
If one bulb in a series circuit fails, all go out. In a parallel circuit, other bulbs remain on because each branch has its own complete loop.
如果串联电路中的一个灯泡损坏，所有灯泡都熄灭。在并联电路中，其他灯泡保持亮着，因为每个支路都有自己完整的回路。
8. Kinetic Energy vs Potential Energy | 动能与势能
Kinetic energy is the energy an object possesses due to its motion. It depends on mass and the square of the speed.
动能是物体由于运动而具有的能量。它取决于质量和速度的平方。
KE = ½ × mass × speed² or KE = ½mv²
Gravitational potential energy (GPE) is the energy stored in an object because of its position in a gravitational field. It depends on mass, gravitational field strength, and height.
重力势能（GPE）是物体因其在重力场中的位置而储存的能量。它取决于质量、重力场强度和高度。
GPE = mass × g × height or PE = mgh
When a ball is thrown upwards, its kinetic energy decreases and GPE increases. At the highest point, kinetic energy is zero (momentarily) and GPE is maximum. On the way down, GPE converts back to kinetic energy.
当一个球向上抛时，它的动能减少而重力势能增加。在最高点，动能（瞬间）为零，GPE最大。下落过程中，重力势能又转回动能。
9. Reflection vs Refraction | 反射与折射
Reflection occurs when a wave bounces off a surface. The angle of incidence equals the angle of reflection, measured from the normal. This applies to light, sound, and water waves.
反射发生在波从表面弹回时。入射角等于反射角，都从法线测量。这适用于光波、声波和水波。
Refraction is the bending of a wave when it passes from one medium to another at an angle, due to a change in speed. Light slows down when entering a denser medium and bends towards the normal.
折射是波以一定角度从一种介质进入另一种介质时，由于速度变化而发生的弯曲。光进入更密的介质时速度减慢，向法线弯曲。
n₁ sin θ₁ = n₂ sin θ₂ (Snell’s law)
In reflection, the wave stays in the same medium, while in refraction the wave transmits into a different medium. A mirror uses reflection; a lens uses refraction to focus light.
在反射中，波保持在同一种介质中，而在折射中，波透入不同的介质。镜子利用反射；透镜利用折射聚焦光线。
10. Nuclear Fission vs Fusion | 核裂变与核聚变
Nuclear fission is the splitting of a large, unstable nucleus (e.g., uranium-235) into two smaller nuclei, releasing a large amount of energy and additional neutrons. This process is used in nuclear power stations.
核裂变是一个大的、不稳定的原子核（如铀-235）分裂成两个较小的原子核，释放大量能量和额外的中子。该过程用于核电站。
Nuclear fusion is the joining of two light nuclei (e.g., isotopes of hydrogen) to form a heavier nucleus (helium), also releasing energy. Fusion powers the Sun and other stars but requires extremely high temperature and pressure.
核聚变是两个轻核（如氢的同位素）结合形成一个较重的核（氦），同样释放能量。聚变为太阳和其他恒星提供动力，但需要极高的温度和压力。
Fission produces radioactive waste and can lead to chain reactions; fusion produces little radioactive waste but is challenging to control on Earth. Both processes demonstrate mass-energy equivalence (E = mc²).
裂变产生放射性废物，并可能引起链式反应；聚变产生的放射性废物很少，但在地球上控制困难。两种过程都体现了质能等价（E = mc²）。
Published by TutorHao | Physics Revision Series | aleveler.com
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