IGCSE Science: Energy – Key Concepts | IGCSE 科学：能量 考点精讲

📚 IGCSE Science: Energy – Key Concepts | IGCSE 科学：能量 考点精讲

Energy is a core topic in IGCSE Science, appearing in both physics problems and chemistry contexts. Understanding energy transfers, conservation, and calculations is essential for exam success. This revision guide covers key concepts, formulas, and practical applications.

能量是IGCSE科学的核心主题，出现在物理问题和化学情境中。理解能量转移、守恒及相关计算对于考试成功至关重要。本考点精讲涵盖关键概念、公式和实际应用。

1. What is Energy? | 能量是什么？

Energy is the ability to do work. It is measured in joules (J).

能量是做功的能力。它用焦耳（J）来度量。

An object or system possesses energy if it can exert a force over a distance, causing a change.

如果物体或系统能够在距离上施加力并引起变化，它就具有能量。

Energy cannot be created or destroyed, only transferred or transformed – this is the law of conservation of energy.

能量不能被创造或毁灭，只能被转移或转化——这就是能量守恒定律。

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2. Forms of Energy | 能量的形式

Kinetic energy – energy of moving objects.

动能 – 运动物体的能量。

Thermal energy – heat energy due to the random motion of particles.

热能 – 由粒子无规则运动产生的热量。

Chemical energy – stored in bonds of chemical compounds; released during reactions.

化学能 – 储存在化合物键中；在反应时释放。

Gravitational potential energy – energy an object has because of its position in a gravitational field.

重力势能 – 物体因在引力场中的位置而具有的能量。

Elastic potential energy – stored in stretched or compressed materials.

弹性势能 – 储存在被拉伸或压缩的材料中。

Nuclear energy – stored in the nucleus of an atom; released in nuclear reactions.

核能 – 储存在原子核中；在核反应中释放。

Electrical energy – energy transferred by moving charges.

电能 – 由电荷运动传递的能量。

Light energy – radiant energy that can be seen or absorbed, e.g. from the Sun.

光能 – 可看见或被吸收的辐射能，例如来自太阳。

Sound energy – carried by vibrations through a medium.

声能 – 通过介质中的振动传递。

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3. Energy Transfers and Transformations | 能量的转移与转化

Energy can be transferred from one store to another. For example, when a ball rolls down a slope, gravitational potential energy is converted to kinetic energy.

能量可以从一个储存形式转移到另一种。例如，球滚下斜坡时，重力势能转化为动能。

A system is an object or group of objects. Energy can leave or enter a system. In a closed system, no energy enters or leaves; total energy remains constant.

系统是一个物体或一组物体。能量可以离开或进入系统。在封闭系统内，无能量进出；总能量保持不变。

Energy transfer diagrams show arrows from one energy store to another, helping to trace pathways. For a light bulb, electrical energy → light energy + thermal energy.

能量转移图用箭头连接不同能量储存，帮助追踪路径。对灯泡而言：电能 → 光能 + 热能。

In many real-world situations, energy is dissipated as thermal energy to the surroundings, making processes less efficient.

在许多实际情况中，能量以热能形式耗散到周围环境，降低了过程的效率。

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4. Conservation of Energy | 能量守恒

The principle of conservation of energy states that energy can never be created or destroyed. It can only be changed from one form to another, or transferred between objects.

能量守恒定律指出，能量永远不能被创造或消灭。它只能从一种形式转化为另一种，或在物体之间转移。

When you observe an apparent ‘loss’ of energy, it has actually been transferred into less useful stores, often thermal energy in the surroundings.

当你观察到能量似乎“损失”时，实际上它已经转移到了用处较小的储存中，通常是周围环境的热能。

This principle underpins all energy calculations in IGCSE Science. For a falling object, loss in gravitational potential energy equals gain in kinetic energy, assuming no air resistance.

这一原理是IGCSE科学中所有能量计算的基础。对于自由下落的物体，重力势能的减少等于动能的增加（假设无空气阻力）。

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5. Work and Energy | 功与能量

Work is done when a force moves an object. The work done (W) is equal to the force (F) multiplied by the distance moved (d) in the direction of the force.

当一个力使物体移动时，就做了功。所做的功（W）等于力（F）乘以沿力方向移动的距离（d）。

W = F × d

Work is measured in joules (J), force in newtons (N), and distance in metres (m).

功的单位是焦耳（J），力的单位是牛顿（N），距离的单位是米（m）。

If a force of 10 N moves an object 5 m, the work done is 50 J. This energy is transferred to the object.

如果一个10 N的力使物体移动5 m，所做的功为50 J。这些能量转移到了物体上。

When work is done against friction, kinetic energy is converted into thermal energy, increasing the temperature of the surfaces.

当克服摩擦力做功时，动能转化为热能，使接触表面温度升高。

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6. Kinetic Energy | 动能

Kinetic energy (Eₖ) is the energy possessed by a moving object. It depends on its mass (m) and speed (v).

动能（Eₖ）是运动物体所具有的能量。它取决于物体的质量（m）和速度（v）。

Eₖ = ½ m v²

Where m is in kilograms (kg), v in metres per second (m/s), and Eₖ in joules (J).

其中 m 的单位是千克（kg），v 的单位是米每秒（m/s），Eₖ 的单位是焦耳（J）。

Doubling the speed quadruples the kinetic energy because velocity is squared. This explains why high-speed collisions are much more damaging.

速度加倍会使动能变为原来的四倍，原因是速度被平方了。这解释了为什么高速碰撞的破坏力要大得多。

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7. Gravitational Potential Energy | 重力势能

Gravitational potential energy (Eₚ) is the energy stored in an object lifted against gravity. It is given by:

重力势能（Eₚ）是物体被举升而克服重力时储存的能量。其公式如下：

Eₚ = m g h

m is mass (kg), g is gravitational field strength (on Earth ≈ 9.8 N/kg, often taken as 10 N/kg in exams), h is height (m).

m 是质量（kg），g 是引力场强度（地球表面约 9.8 N/kg，考试中常取 10 N/kg），h 是高度（m）。

When an object falls, Eₚ is converted to kinetic energy. If air resistance is negligible, mgh lost = ½ mv² gained.

当物体下落时，重力势能转化为动能。如果空气阻力忽略不计，那么失去的 mgh 等于获得的 ½ mv²。

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8. Power | 功率

Power is the rate at which energy is transferred or work is done. It tells us how quickly energy is used.

功率是能量转移或做功的速率。它告诉我们能量被使用的快慢。

P = E / t or P = W / t

Power (P) is measured in watts (W), where 1 W = 1 J/s. Energy in joules, time in seconds.

功率（P）的单位是瓦特（W），1 W = 1 J/s。能量单位焦耳，时间单位秒。

A more powerful motor can do the same amount of work in less time. For example, a 2000 W kettle transfers 2000 J of energy every second.

功率更大的马达可以在更短的时间内完成等量的功。例如，一个 2000 W 的电水壶每秒转移 2000 J 的能量。

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9. Energy Resources | 能源

Energy resources are used to generate electricity and provide fuel. They can be renewable or non-renewable.

能源被用来发电和提供燃料。它们可分为可再生和不可再生两大类。

Renewable (可再生)	Non-renewable (不可再生)
Solar energy (太阳能)	Fossil fuels: coal, oil, natural gas (化石燃料：煤、石油、天然气)
Wind energy (风能)	Nuclear fuel (e.g. uranium) (核燃料，如铀)
Hydroelectric power (水电)
Tidal and wave energy (潮汐能和波浪能)
Geothermal energy (地热能)
Biomass (生物质能)

Non-renewable resources are finite and will run out. Burning fossil fuels releases carbon dioxide, contributing to climate change. Nuclear power produces radioactive waste.

不可再生资源是有限的，终将耗尽。燃烧化石燃料会释放二氧化碳，加剧气候变化。核能会产生放射性废物。

Renewable resources are replenished naturally. Many do not emit greenhouse gases during operation, but they can be weather-dependent and have high initial costs.

可再生资源自然补充。许多在运行中不排放温室气体，但它们可能受天气影响，且初始成本较高。

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10. Efficiency | 效率

Efficiency measures how much of the total energy input is converted to useful output. No device is 100% efficient because some energy is always wasted, usually as heat.

效率衡量总输入能量中有多少转化为有用的输出。没有任何设备是 100% 高效的，因为总有一些能量被浪费，通常以热的形式。

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

效率 = (有用的输出能量转移 / 总输入能量转移) × 100%

Efficiency can also be calculated using power: Efficiency = (Useful power output / Total power input) × 100%.

效率也可以用功率计算：效率 = (有用输出功率 / 总输入功率) × 100%。

For an electric motor that lifts a weight, if 200 J of electrical energy is supplied and the motor does 150 J of work against gravity, the efficiency is (150/200) × 100% = 75%.

对于一个用于提升重物的电动机，如果输入 200 J 的电能，电动机克服重力做功 150 J，其效率为 (150/200) × 100% = 75%。

Improving efficiency reduces energy waste and operational costs. Simple methods include lubrication to reduce friction and better insulation to minimise heat loss.

提高效率可以减少能量浪费和运行成本。简单的方法包括润滑以减少摩擦，以及改善隔热以减少热量损失。

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11. Heat Transfer and Energy | 热传递与能量

Thermal energy can be transferred by conduction, convection, and radiation. These processes are important in many energy systems.

热能可以通过传导、对流和辐射进行传递。这些过程在许多能量系统中非常重要。

Conduction—transfer of heat through solids by particle vibrations. Metals are good conductors because of free electrons. Non-metals and gases are insulators.

传导——通过粒子振动在固体中传递热量。金属因自由电子而成为良导体。非金属和气体是绝缘体。

Convection—occurs in fluids (liquids and gases). Warmer, less dense regions rise, cooler regions sink, setting up a convection current.

对流——发生在流体（液体和气体）中。较热、密度较小的区域上升，较冷区域下沉，形成对流循环。

Radiation—transfer of energy by infrared waves; does not require a medium. All objects emit and absorb thermal radiation; dark, matt surfaces are the best absorbers and emitters.

辐射——通过红外波传递能量；不需要介质。所有物体都发射和吸收热辐射；深色、粗糙的表面是最好的吸收体和发射体。

In an insulated house, trapped air reduces heat loss by convection and conduction, and reflective foils cut radiation losses.

在隔热的房屋中，被封闭的空气能减少对流和传导导致的热量散失，反光箔则可减少辐射损失。

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