IGCSE CIE Science: Energy Revision | IGCSE CIE 科学：能量考点精讲

📚 IGCSE CIE Science: Energy Revision | IGCSE CIE 科学：能量考点精讲

Energy is one of the most fundamental concepts in IGCSE CIE Science. It underpins everything from the motion of a racing car to the growth of a plant. In your Coordinated Sciences or Physics exam, you must understand how energy is stored, transferred, and conserved, as well as how to calculate work, power, and efficiency. This revision guide breaks down every key topic you need to master.

能量是 IGCSE CIE 科学中最基础的概念之一，从赛车的运动到植物的生长，无不涉及能量。在综合性科学或物理考试中，你需要理解能量如何储存、转移和守恒，以及如何计算功、功率和效率。这篇复习指南将分解你需要掌握的每一个关键主题。

1. What is Energy? | 能量是什么？

Energy is defined as the capacity to do work. It is a scalar quantity, meaning it has magnitude but no direction. The SI unit of energy is the joule (J). One joule is the energy transferred when a force of one newton acts over a distance of one metre.

能量被定义为做功的能力。它是一个标量，即只有大小没有方向。能量的国际单位是焦耳（J）。当 1 牛顿的力作用在物体上使其移动 1 米时，转移的能量就是 1 焦耳。

Energy cannot be created or destroyed. This statement is known as the principle of conservation of energy. It can only be transferred from one form to another or moved from one place to another. The total energy in a closed system always remains constant.

能量不能被创造或消灭。这一表述被称为能量守恒定律。能量只能从一种形式转化为另一种形式，或从一个地方转移到另一个地方。在一个封闭系统中，总能量始终保持不变。

2. Forms of Energy | 能量的形式

In IGCSE Science, you are expected to identify and describe eight main forms of energy. These are kinetic energy, gravitational potential energy, elastic potential energy, thermal (heat) energy, chemical energy, electrical energy, light energy, and sound energy. Nuclear energy is also mentioned in the context of energy resources.

在 IGCSE 科学中，你需要识别并描述八种主要的能量形式：动能、重力势能、弹性势能、热（内）能、化学能、电能、光能和声能。核能则在能源资源的背景下被提及。

Kinetic energy: energy of a moving object.
Gravitational potential energy: energy stored in an object raised above the ground.
Elastic potential energy: energy stored in a stretched or compressed spring.
Thermal energy: energy related to the temperature of an object, due to the random motion of its particles.
Chemical energy: energy stored in chemical bonds, released during reactions.
Electrical energy: energy carried by moving charges.
Light energy: energy carried by electromagnetic waves visible to the eye.
Sound energy: energy carried by longitudinal waves through a medium.

动能：运动物体的能量。
重力势能：被举高的物体储存的能量。
弹性势能：拉伸或压缩的弹簧储存的能量。
热能：与物体温度相关的能量，源于粒子无规则运动。
化学能：储存在化学键中的能量，在化学反应中释放。
电能：移动电荷携带的能量。
光能：人眼可见的电磁波携带的能量。
声能：通过介质传播的纵波携带的能量。

3. Kinetic Energy and Gravitational Potential Energy | 动能和重力势能

Two of the most frequently calculated forms of energy are kinetic energy (KE) and gravitational potential energy (GPE). The kinetic energy of an object depends on its mass and speed. The formula is:

KE = ½ × m × v²

where m is mass in kilograms (kg) and v is speed in metres per second (m/s). KE is measured in joules.

两种最常计算的能量形式是动能（KE）和重力势能（GPE）。物体的动能取决于它的质量与速度。公式为：动能 = ½ × 质量 × 速度的平方，其中 m 是质量（kg），v 是速度（m/s），动能的单位是焦耳。

Gravitational potential energy depends on mass, gravitational field strength, and height. The formula is:

GPE = m × g × h

Here m is mass in kilograms, g is the gravitational field strength (on Earth approximately 9.8 N/kg, but often taken as 10 N/kg in exam problems), and h is the height in metres above a reference point.

重力势能取决于质量、引力场强度和高度。公式为：GPE = 质量 × 引力场强度 × 高度。其中 m 是质量（kg），g 是引力场强度（地球表面约为 9.8 N/kg，考试中常取 10 N/kg），h 是相对于参考点的高度（m）。

In many problems, energy is transferred between KE and GPE with no overall loss. For example, when an object falls, GPE is converted to KE, and the sum remains constant if air resistance is negligible.

在许多问题中，能量在动能和重力势能之间转换而无总损失。例如，当物体下落时，重力势能转化为动能，如果空气阻力可忽略，总和保持不变。

4. Energy Conservation and Transfer | 能量守恒与转移

The principle of conservation of energy is central to all energy questions. It states: Energy can be transferred, stored, or dissipated, but it can never be created or destroyed. In any energy transfer, the total input energy equals the total output energy.

能量守恒定律是所有能量问题的核心。它指出：能量可以被转移、储存或耗散，但绝不能被创造或毁灭。在任何能量转移过程中，总输入能量等于总输出能量。

Energy transfers can be described using diagrams or written pathways. For instance, in a battery-powered torch, the energy transfer is: chemical energy in the battery → electrical energy in the wires → light energy and thermal energy from the bulb. The thermal energy is often described as ‘wasted’ or ‘dissipated’.

能量转移可以用图示或文字路径描述。例如，在一个电池供电的手电筒中，能量转移过程是：电池中的化学能 → 导线中的电能 → 灯泡的光能和热能。其中热能通常被描述为“浪费的”或“耗散的”能量。

Four common ways of transferring energy are: mechanically (by a force doing work), electrically (by charges moving through a circuit), by heating (due to temperature difference), and by radiation (such as light or sound waves).

四种常见的能量转移方式为：通过机械做功（力做功）、通过电路（电荷移动）、通过加热（温度差引起）和通过辐射（如光波或声波）。

5. Work | 功

Work is done whenever a force moves an object. In scientific terms, work is the product of the force and the distance moved in the direction of the force. It is a measure of energy transfer.

每当力使物体在力的方向上移动一段距离时，就做了功。在科学上，功是力与在力方向上移动距离的乘积，是能量转移的量度。

W = F × d

where W is work in joules (J), F is the force in newtons (N), and d is the distance in metres (m). If the force is not in the same direction as the movement, only the component of force in the direction of motion does work.

其中 W 是功（J），F 是力（N），d 是沿力方向移动的距离（m）。如果力与运动方向不一致，只有力在运动方向上的分量才做功。

It is important to note that holding a heavy object stationary does no work on the object, even if it feels tiring. Work is done only when there is movement in the direction of the force.

需要注意的是，即使静止地举着重物感觉很累，但没有对物体做功。只有在力的方向上发生移动时，才做了功。

6. Power | 功率

Power is the rate at which work is done or the rate at which energy is transferred. It tells us how quickly energy is being used or produced. The unit of power is the watt (W), where 1 W = 1 J/s.

功率是做功的速率或能量转移的速率。它告诉我们能量被使用或产生的快慢。功率的单位是瓦特（W），1 W = 1 J/s。

The formula linking power, work, and time is:

P = W / t

Since work is energy transferred, this can also be written as P = E / t. Here P is power in watts (W), E or W is energy or work in joules (J), and t is time in seconds (s).

由于功是转移的能量，这个公式也可写成 P = E / t。其中 P 是功率（W），E 或 W 是能量或功（J），t 是时间（s）。

A more powerful machine does the same amount of work in less time, or more work in the same time. In exam questions, you may be asked to calculate power from given values of work and time, or to compare the power of two different devices.

功率更大的机器能在更短时间内做相同的功，或在相同时间内做更多的功。考试中可能会要求你根据给出的功和时间计算功率，或比较两种不同装置的功率。

7. Efficiency | 效率

No energy transfer is perfectly efficient. In every process, some energy is converted into less useful forms, usually thermal energy, which dissipates into the surroundings. Efficiency measures how much of the input energy is transferred usefully.

没有一种能量转移是完全有效的。在每个过程中，都会有一部分能量转化为不太有用的形式，通常是散失到周围环境中的热能。效率衡量的是有多少输入能量被有效地转移为有用能量。

Efficiency can be calculated using the equation:

Efficiency = (Useful output energy / Total input energy) × 100%

Alternatively, it can be expressed in terms of power: Efficiency = (Useful power output / Total power input) × 100%. Efficiency is always between 0% and 100%, and it can be given as a decimal or a percentage.

也可以用功率表示：效率 = （有用输出功率 / 总输入功率）× 100%。效率始终介于 0% 到 100% 之间，可以用小数或百分数表示。

For example, if an electric motor receives 500 J of electrical energy and does 350 J of useful mechanical work, its efficiency is (350/500) × 100% = 70%. The remaining 150 J is wasted as thermal energy and sound.

例如，一台电动机接收 500 J 的电能，做了 350 J 的有用机械功，则其效率为 (350/500) × 100% = 70%。剩余 150 J 以热能和声能的形式浪费掉。

8. Sankey Diagrams | 桑基图

Sankey diagrams are flow diagrams that represent energy transfers visually. The width of each arrow is proportional to the amount of energy it represents. They make it easy to compare useful output energy with wasted energy.

桑基图是直观表示能量转移的流程图。每个箭头的宽度与其代表的能量大小成比例。它们使有用输出能量和浪费能量的比较变得一目了然。

In a typical Sankey diagram, the total input energy is shown as a thick arrow entering the system. This arrow then splits into branches: a useful energy output arrow and one or more wasted energy arrows. The widths of all output arrows add up to the width of the input arrow, showing conservation of energy.

在典型的桑基图中，总输入能量以进入系统的粗箭头表示。这个箭头随后分叉：一个有用的能量输出箭头和一个或多个浪费能量箭头。所有输出箭头的宽度加起来等于输入箭头的宽度，体现了能量守恒。

IGCSE questions may ask you to complete a partly drawn Sankey diagram, calculate efficiency from the widths, or draw a simple diagram for a device such as a light bulb or a television.

IGCSE 题目可能会要求你补全一个部分绘制的桑基图，根据宽度计算效率，或为灯泡、电视机等设备绘制简单示意图。

9. Energy Resources | 能源

Energy resources are sources from which we obtain useful energy. They are classified as renewable or non-renewable. Non-renewable resources include fossil fuels (coal, oil, natural gas) and nuclear fuels (uranium). These are finite and will eventually run out.

能源是我们从中获取有用能量的来源。它们分为可再生能源和不可再生能源。不可再生能源包括化石燃料（煤、石油、天然气）和核燃料（铀），它们是有限的，终将耗尽。

Renewable energy resources can be replenished in a short time scale. Examples are solar energy, wind energy, wave energy, hydroelectric power, tidal energy, geothermal energy, and biofuels. Many renewable resources are weather-dependent and may have variable output.

可再生能源能在较短时间内得到补充，例如太阳能、风能、波浪能、水力发电、潮汐能、地热能和生物燃料。许多可再生能源依赖于天气，输出功率可能不稳定。

Each energy resource has advantages and disadvantages in terms of reliability, environmental impact, cost, and carbon emissions. In the exam, you may need to evaluate which resource is most suitable for a given situation, such as a remote island or a large city.

每种能源在可靠性、环境影响、成本和碳排放方面各有优缺点。考试中，你可能需要评估哪种资源最适合特定情境，例如偏远的岛屿或大城市。

Resource	Renewable?	Main advantage	Main disadvantage
Coal	No	Reliable, high power output	Releases CO₂, SO₂, non-renewable
Wind	Yes	No CO₂ emissions after construction	Unreliable, visual and noise pollution
Solar	Yes	Clean, free after setup	Intermittent, requires large area
Nuclear	No	Very high energy density, low CO₂	Radioactive waste, risk of accidents

10. Thermal Energy Transfer: Conduction, Convection, Radiation | 热能传递：传导、对流、辐射

Thermal energy can be transferred by three mechanisms: conduction, convection, and radiation. Conduction is the transfer of heat through a solid without the movement of the material itself. It occurs mainly in solids and is due to particles colliding and passing on kinetic energy. Metals are good conductors because of free electrons.

热能可以通过三种机制传递：传导、对流和辐射。传导是在固体中热量不伴随物质本身移动的传递方式，主要发生在固体中，源于粒子碰撞并传递动能。金属因自由电子而成为良导体。

Convection is the transfer of heat through a fluid (liquid or gas) by the movement of the fluid itself. Warmer, less dense fluid rises, and cooler, denser fluid sinks, creating a convection current. This is how rooms are heated by radiators and how sea breezes form.

对流是通过流体（液体或气体）自身的运动来传热的方式。较热、密度较小的流体上升，较冷、密度较大的流体下沉，形成对流循环。暖气片加热房间和海陆风的形成都是这个原理。

Radiation is the transfer of energy via electromagnetic waves, primarily infrared radiation. It does not require a medium and can travel through a vacuum. All objects emit and absorb thermal radiation. Dark, matt surfaces are better absorbers and emitters of infrared radiation than light, shiny surfaces.

辐射是通过电磁波（主要是红外线）传递能量。它不需要介质，可以在真空中传播。所有物体都会发射和吸收热辐射。暗色、粗糙的表面比浅色、光滑的表面更善于吸收和发射红外辐射。

In IGCSE experiments, you often investigate factors affecting radiation by comparing temperature changes of different surfaces. Conduction and convection are studied through simple experiments with heated rods or liquids.

在 IGCSE 实验中，你经常通过比较不同表面的温度变化来研究影响辐射的因素。传导和对流则通过加热金属棒或液体的简单实验进行研究。

11. Energy in Food and Fuels | 食物与燃料中的能量

Chemical energy is stored in food and fuels. When these substances undergo combustion or respiration, energy is released. The energy content of food and fuels can be measured using a calorimeter or a simple burning experiment. The amount of energy released is calculated by measuring the temperature rise of a known mass of water.

化学能储存在食物和燃料中。这些物质在燃烧或呼吸作用中释放能量。食物和燃料的能量含量可以用量热计或简单的燃烧实验来测量。通过测量已知质量水的温升，可以计算出释放的能量。

Energy transferred = m × c × Δθ

where m is the mass of water (kg), c is the specific heat capacity of water (4200 J/kg°C), and Δθ is the temperature rise (°C). This formula appears more frequently in Physics, but Combined Science students may encounter it in energy context questions.

其中 m 是水的质量（kg），c 是水的比热容（4200 J/kg°C），Δθ 是温度升高值（°C）。这个公式更多出现在纯物理中，但综合科学的学生也可能在能量相关题目中遇到它。

You should be able to describe methods to compare the energy per gram of different fuels or foods, identifying sources of error such as heat loss to the surroundings. This topic links chemical energy to thermal transfer and reinforces the concept of energy conservation.

你应该能够描述比较不同燃料或食物每克能量的方法，并找出实验误差来源，如向环境散热。该主题将化学能与热传递联系起来，强化了能量守恒的概念。

12. Practical Skills and Exam Tips | 实验技能与考试技巧

IGCSE CIE Science assesses energy through calculation questions, graph interpretation, and practical-based tasks. Make sure you can rearrange formulas confidently. For example, given mass and speed, find KE; or given height and mass, find GPE. Use the rearrangement triangle or algebra.

IGCSE CIE 科学通过计算题、图表解读和实践任务来考查能量知识。确保你能自信地变换公式，比如已知质量和速度求动能，或已知高度和质量求重力势能。使用变换三角形或代数方法。

When analyzing systems, always consider energy dissipation. In many contexts, the useful energy output is less than the input because of friction, air resistance, or resistance in wires. Show how energy is conserved by accounting for all output forms.

分析系统时，始终要考虑能量耗散。在很多情况下，有用能量输出小于输入，因为有摩擦、空气阻力或导线电阻。通过列出所有输出能量形式来体现能量守恒。

Read Sankey diagram scales carefully. The width of arrows may represent energy per second or total energy. Use a ruler if necessary to compare widths. For efficiency questions, always check if the answer should be in decimal or percentage form.

仔细阅读桑基图的标度。箭头宽度可能代表每秒能量或总能量。必要时用尺子比较宽度。对于效率题目，始终确认答案是小数形式还是百分数形式。

Familiarize yourself with common practicals, such as measuring the energy released by burning a peanut, or plotting cooling curves for different surfaces. Questions often ask why a substance is stirred (to ensure uniform temperature) or why a lid is used (to reduce heat loss).

熟悉常见的实验操作，如测量燃烧花生释放的能量，或绘制不同表面的冷却曲线。题目常问为什么要搅拌物质（确保温度均匀）或为什么要使用盖子（减少热量损失）。

最后，请记住所有的能量计算最终都回到一个核心观念：能量既不会凭空产生也不会凭空消失，它只会从一种形式转换为另一种形式。掌握这一点，你就掌握了 IGCSE 科学能量章节的精髓。

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IGCSE CIE Science: Energy Revision | IGCSE CIE 科学：能量 考点精讲