📚 IGCSE OCR Physics: Mind Map Quick Revision | IGCSE OCR 物理：思维导图速记
This mind map style quick revision guide summarises the most important concepts, equations and definitions for the IGCSE OCR Physics syllabus. Use it to connect ideas and secure key knowledge before your exam.
这篇思维导图式快速复习指南总结了 IGCSE OCR 物理大纲中最重要的概念、公式和定义。用它来串联思路，巩固关键知识，备战考试。
1. Matter and Thermal Physics | 物质与热学
States of matter: a solid has a fixed shape and a fixed volume, a liquid has a fixed volume but takes the shape of its container, and a gas has neither a fixed shape nor a fixed volume. Intermolecular forces are strongest in solids and weakest in gases, which is why solids keep their shape while gases fill any container.
物质状态：固体有固定的形状和体积，液体有固定的体积但形状随容器改变，气体既没有固定形状也没有固定体积。分子间作用力在固体中最强、在气体中最弱，所以固体能保持形状而气体能充满容器。
Density is the mass per unit volume and shows how tightly the particles are packed. An object floats if its density is less than the fluid's density of the fluid and sinks if it is greater. Units are kg/m³ or g/cm³.
密度是单位体积的质量，反映粒子排列的紧密程度。若物体密度小于流体密度则上浮，大于流体密度则下沉。单位是 kg/m³ 或 g/cm³。
ρ = m / V
1 g/cm³ = 1000 kg/m³
Internal energy is the total kinetic energy plus the total potential energy of all the particles in a body. Heating increases internal energy. During a change of state the temperature stays constant because the energy supplied increases the potential energy of the particles rather than their kinetic energy.
内能是物体内所有粒子的总动能与总势能之和。加热会增加内能。状态改变时温度保持不变，因为所供给的能量增加了粒子的势能，而不是动能。
Specific heat capacity c is the energy needed to raise the temperature of 1 kg of a substance by 1 °C. Water has a very high value, about 4200 J/kg°C, which is why it is used in heating systems and why coastal climates are milder.
比热容 c 是使 1 kg 物质温度升高 1 °C 所需的能量。水的比热容很高，约 4200 J/kg°C，因此常用于供暖系统，也解释了沿海气候更温和的原因。
E = m c Δθ
Specific latent heat L is the energy needed to change the state of 1 kg of a substance with no temperature change. Latent heat of fusion covers solid to liquid, and latent heat of vaporisation covers liquid to gas.
比潜热 L 是使 1 kg 物质发生状态改变而温度不变所需的能量。熔化潜热对应固-液变化，气化潜热对应液-气变化。
L = E / m
a fixed mass of gas at constant temperature, pressure × volume is constant. This is Boyle' with the container walls, so compressing a gas raises the collision rate and the pressure.
气体定律：一定质量的气体在温度不变时，压强 × 体积为常数，这就是玻意耳定律，写作 p₁V₁ = p₂V₂。压强由粒子碰撞容器壁产生，因此压缩气体使碰撞频率升高，压强增大。
p₁ V₁ = p₂ V₂
Temperature in kelvin is found by adding 273 to the Celsius value, and 0 K is absolute zero, where particles have minimum kinetic energy.
开尔文温度等于摄氏温度加 273，0 K 是绝对零度，此时粒子动能最小。
T (K) = θ (°C) + 273
2. Forces and Motion | 力与运动
Scalar quantities have magnitude only, for example speed, distance, mass and energy. Vector quantities have magnitude and direction, for example velocity, displacement, force, acceleration and momentum. Vectors are added by drawing them tip to tail.
标量只有大小，例如速率、路程、质量和能量。矢量既有大小又有方向，例如速度、位移、力、加速度和动量。矢量相加可用首尾相接的作图法。
Speed is distance travelled per second and velocity is speed in a stated direction. Acceleration is the change in velocity per second, so a negative value means deceleration.
速率是每秒通过的路程，速度是带有方向说明的速率。加速度是每秒速度的变化量，负值表示减速。
v = s / t a = (v − u) / t
On a distance-time graph the gradient gives speed. On a velocity-time graph the gradient gives acceleration and the area under the line gives the distance travelled.
路程-时间图的斜率表示速率。速度-时间图的斜率表示加速度，图线下方的面积表示通过的路程。
The resultant force is the single force that has the same effect as all the forces acting together. If the resultant force is zero the object stays at rest or moves at constant velocity; if it is not zero the object accelerates in the direction of the resultant force.
合力是所有力共同作用的等效单一力。若合力为零，物体保持静止或匀速运动；若合力不为零，物体沿合力方向加速。
F = m a W = m g
Weight is the force of gravity on a mass, with g about 9.8 N/kg near the Earth's surface. Mass is the amount of matter in an object and does not change with location, while weight does.
重力是作用在质量上的引力，地球表面附近 g 约为 9.8 N/kg。质量是物体所含物质的多少，不随位置改变，而重力会改变。
Hooke's law states that the extension of a spring is directly proportional to the force applied, up to the limit of proportionality. The gradient of a force-extension graph gives the spring constant k in N/m.
胡克定律指出，在比例极限内弹簧的伸长量与所施加的力成正比。力-伸长量图的斜率给出弹簧常数 k，单位为 N/m。
F = k x
Momentum is the product of mass and velocity and is a vector. In a closed system the total momentum before a collision or explosion equals the total momentum afterwards, which is the principle of conservation of momentum.
动量是质量与速度的乘积，属于矢量。在封闭系统中，碰撞或爆炸前的总动量等于之后的总动量，这就是动量守恒定律。
p = m v m₁u₁ + m₂u₂ = m₁v₁ + m₂v₂
Stopping distance is the sum of thinking distance and braking distance. Thinking distance increases with reaction time, alcohol, tiredness and speed; braking distance increases with speed, poor brakes and slippery roads, because kinetic energy depends on the square of the speed.
停车距离等于反应距离加制动距离。反应距离随反应时间、酒精、疲劳和车速增加；制动距离随车速、刹车不良和路面湿滑增加，因为动能与速度的平方成正比。
3. Work, Energy and Power | 功、能量与功率
Work is done when a force moves an object through a distance in the direction of the force. One joule of work is done when a force of one newton moves an object one metre.
当力使物体沿力的方向移动一段距离时，就做了功。1 牛的力使物体移动 1 米所做的功是 1 焦耳。
W = F d
Kinetic energy is the energy of a moving object and gravitational potential energy is the energy stored by an object raised above the ground. Both are measured in joules.
动能是运动物体具有的能量，重力势能是物体被举高后储存的能量。两者单位都是焦耳。
Eₖ = ½ m v² Eₚ = m g h
The principle of conservation of energy states that energy cannot be created or destroyed, only transferred between stores. In a falling object, gravitational potential energy transfers to kinetic energy and to thermal energy through air resistance.
能量守恒定律指出，能量既不能创生也不能消灭，只能在不同的能量库之间转移。物体下落时，重力势能转化为动能，并通过空气阻力转化为热能。
Efficiency compares the useful energy output with the total energy input, and is usually expressed as a percentage. A Sankey diagram shows the useful and wasted energy transfers with arrows whose widths are proportional to the energy involved.
效率是比较有用能量输出与总能量输入的比值，通常用百分比表示。桑基图用箭头表示有用和浪费的能量转移，箭头宽度与能量大小成正比。
efficiency = useful output energy / total input energy × 100%
ts, where 1 W = 1 J/s. A more powerful device transfers the same energy in a shorter time.
功率是能量转移的速率或做功的速率，单位为瓦特，1 W = 1 J/s。功率更大的装置在更短时间内转移相同的能量。
P = E / t = W / t
Thermal energy is transferred by conduction in solids when vibrating particles pass energy along, by convection in fluids when warm fluid rises and cooler fluid sinks, and by radiation as infrared waves that need no medium. Dark, matt surfaces are good absorbers and emitters of infrared; shiny, light surfaces are good reflectors.
热传递有三种方式：固体中通过粒子振动依次传递是传导；流体中热流体上升、冷流体下沉形成对流；辐射是以红外波传递，不需要介质。深色、粗糙表面是红外线的良好吸收体和发射体；光亮、浅色表面是良好的反射体。
4. Waves and Sound | 波与声
Waves transfer energy without transferring matter. Transverse waves have vibrations perpendicular to the direction of travel, such as light and water waves; longitudinal waves have vibrations parallel to the direction of travel, such as sound.
波传递能量而不传递物质。横波的振动方向与传播方向垂直，例如光和水的表面波；纵波的振动方向与传播方向平行，例如声波。
Amplitude is the maximum displacement from the rest position, wavelength is the distance between two identical points on the wave, and frequency is the number of waves passing a point each second, measured in hertz. The period is the time for one complete wave.
振幅是离开平衡位置的最大位移，波长是波上两个相同点之间的距离，频率是每秒通过某点的波数，单位是赫兹。周期是完成一个完整波所需的时间。
v = f λ f = 1 / T
All waves can be reflected, refracted and diffracted. Reflection is bouncing off a surface, refraction is a change of speed and direction when entering a different medium, and diffraction is spreading out when passing through a gap or around an obstacle.
所有波都能发生反射、折射和衍射。反射是从表面弹回，折射是进入不同介质时速度和方向发生改变，衍射是绕过障碍物或通过狭缝后发生扩散。
The law of reflection states that the angle of incidence equals the angle of reflection, both measured from the normal. When light passes from air into glass it slows down and bends towards the normal; leaving glass it speeds up and bends away.
反射定律指出入射角等于反射角，均从法线量起。光从空气进入玻璃时速度减慢并向法线偏折；离开玻璃时速度加快并偏离法线。
Sound is produced by vibrating sources and travels as a longitudinal wave, needing a medium. A higher frequency gives a higher pitch and a larger amplitude gives a louder sound. Sound is reflected as an echo, and ultrasound above 20 kHz is used in medical scanning and sonar.
声音由振动的物体产生，以纵波形式传播，必须依靠介质。频率越高音调越高，振幅越大声音越响。声音反射形成回声，高于 20 kHz 的超声波用于医学扫描和声呐。
Wave speed depends on the medium. In a ripple tank, a higher frequency gives a shorter wavelength when the wave speed stays the same, and this explains why refraction happens when wave speed changes.
波速取决于介质。在水波槽中，若波速不变，频率越高波长越短，这也解释了波速改变时发生折射的原因。
5. Light, Optics and the Electromagnetic Spectrum | 光、光学与电磁波谱
A plane mirror forms a virtual image that is the same size as the object, as far behind the mirror as the object is in front, and laterally inverted. Ray diagrams for mirrors and lenses should always be drawn with a ruler, arrows on rays and the normal for reflection and refraction.
平面镜成虚像，大小与物体相同，像距等于物距，并且左右颠倒。画镜面和透镜的光路图时必须用直尺、标出光线箭头，并在反射和折射处画出法线。
Total internal reflection happens when light travels from a denser to a less dense medium and the angle of incidence is greater than the critical angle. It is used in optical fibres for communication and in endoscopes, because the signal stays inside the fibre.
全反射发生在光从光密介质射向光疏介质、且入射角大于临界角时。它用于通信光纤和内窥镜，因为信号被完全限制在纤维内部传播。
, ultraviolet, X-rays and gamma rays. All travel at the same speed in a vacuum, 3.0 × 10⁸ m/s.
电磁波谱按频率升高、波长减小的顺序为：无线电波、微波、红外线、可见光、紫外线、X 射线和伽马射线。它们在真空中传播速度相同，均为 3.0 × 10⁸ m/s。
- Radio waves: communication and broadcasting. 无线电波：通信与广播。
- Microwaves: satellite links, mobile phones and cooking. 微波：卫星通信、手机与加热食物。
- Infrared: heaters, remote controls and thermal imaging. 红外线：取暖器、遥控器与热成像。
- Visible light: vision, photography and optical fibres. 可见光：视觉、摄影与光纤。
- Ultraviolet: sterilising and sun tanning, but it can damage skin and eyes. 紫外线：杀菌与晒黑，但会伤害皮肤和眼睛。
- X-rays: medical imaging, but they ionise cells. X 射线：医学成像，但会电离细胞。
- Gamma rays: sterilising equipment and treating cancer, but highly ionising. 伽马射线：消毒器械与治疗癌症，但电离性很强。
White light disperses into a spectrum when it passes through a prism because each colour refracts by a different amount. Red refracts least and violet refracts most. A coloured filter transmits only its own colour and absorbs the rest.
白光通过棱镜时因各色光折射程度不同而色散成光谱。红光偏折最小，紫光偏折最大。彩色滤光片只透过自身颜色的光，吸收其他颜色。
A converging lens brings parallel rays to the principal focus and can form a real, inverted image or a virtual, magnified image when the object is inside the focal length. A diverging lens always forms a virtual, upright, diminished image.
凸透镜使平行光会聚到主焦点，可成实像（倒立）或当物体在焦距以内时成虚像（放大）。凹透镜总是成虚像、正立、缩小。
6. Electricity and Circuits | 电与电路
Electric current is the rate of flow of charge, measured in amperes, and charge is measured in coulombs. One ampere is one coulomb per second. In metals the charge carriers are electrons; in electrolytes they are ions.
电流是电荷流动的速率，单位为安
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