22-1基础物理学讲义Electromagnetic Waves
or
mT 2898μm K
Wien’s displacement law
proposed by Wien in 1893
In 1869 Wien proposed a formula empirically from experimental data:
u( ,T )d ~ 3e T d ~ e T 2d.
photoelectrons photoelectric current ~ I
Tmax eV0 ?~ I incident
stopping potential
Experiments show Tmax~ C below it, no ... 10 – 9s after irradiation
Blackbody a complete black object that reflects none of the radiation that strikes it.
A cavity with a small hole Radiation from outside that strikes the hole gets lost inside the cavity.
V0
h
e
f
e
1916 Millikan
1923 Nobel prize was awarded to Millikan for his work on the elementary charge of electricity and on the photoelectric effect.
1889 Max Planck proposed a new formula
u( ,T )d
8 2
c3
h
eh
1
d
Or, equivalently
u(,T )
8π
4
hc 1
eβ
hcλ
dλ 1
.
u( ,T )d
8 2
c3
e
h
h
1
d
high limit
: u( ,T )d
8h
Wien’s formula
Rayleigh-Jeans law (1900-1905) Lord Rayleigh, Sir James Jeans
1. The cavity is filled with the electromagnetic standing wave.
2. The number of standing waves with frequencies
is just the energy current 1
2
3
density ju
ju
1 4
u
c.
see effusion §13.4
The experimental results
1. Stefan-Boltzmann law
ju
R( ,T )d
T 4.
0
5.67 108W m2 K 4.
The 1918 Nobel Prize was awarded to Planck for his discovery of energy quanta.
22.2 Photoelectric effect
ultraviolet light
+
In 1888, Hallwachs found photoelectric effect
This is against the second law of thermodynamics.
Therefore, in equilibrium, the energy density of the
radiation in a cavity is function of temperature alone.
quanta:
E nh.
nhenh
n
enh
h
e h
. 1
n
From
R( ,T )d T 4,
0
we can obtain
2 5kB4
15c2h3
,
and
h 6.6261034 Js.
The constant h has fundamental significance. which has no counterpart in classical physics.,
u u( ,T ) or u u(,T ).
If the energy density of the radiation depends on other properties so that
u( ,T ,x) u( ,T ,y),
a perpetual machine of second kind will become possible.
0
the radiated energy current
R( )d density of the radiation with
frequency in a range d
R( ) the radiant intensity
prism
The total radiant intensity
0 R( )d
between and +d is
N( )d
8V
c3
2
d
where V is the volume of the cavity.
3.Each individual standing wave contributes an
energy kBT to the radiation in the cavity. Then, the energy density is
British physicist Lord Kelvin (W. Thomson)
“In the remote part of sunny sky of physics there are two small puzzling dark clouds.”
Michelson Morley experiment blackbody radiation
Example 22.1
~m
~W
power P0 ~ W; intensity is P0 / 4r2 absorbed power is
P
~
I
a2
P0
a
2
~
W
Å
m
2
4 r
To escape, the electron has to accumulate an amount of
energy about eV in a time interval t
Planck announced the result in 1900. There were no shock waves. Planck himself believed that he had just found a ad hoc explanation.
It was not until after 1911 that Planck fully appreciated the absolutely fundamental nature of quantization
u u( ,T ), [u u(,T )].
the energy density of the radiation in a cavity per unit range of frequency[wavelength].
the energy density of the radiation
u(T ) u( ,T )d
Part IV Fundamental Modern Physics
Chapter 22 Energy Quantization
discreteness the existence of fundamental unit
g
G c3
1.6
1035 m
e 1.602177331019C
At the end of 19th century, most physicists thought that the mansion of classical physics was basically established, the work left for the physicists would be just mending.
Critical frequency C
h f Tmax
0
f
h
C
Example 22.2 Critical wavelength and frequency
for Na and Pt
green-yellow visible
C (Na)
hc
f
1240eV nm 2.28eV
543 nm
C (Na)
22.1 Blackbody radiation
Thermal radiation (infrared-visible-ultraviolet) emitted by ordinary objects depends not only on the temperature, but also on other properties such as • shape • surface properties • material of which it is constructed • whether or not it reflects the radiation the falls on from its surroundings
u( )d
8 2
c3
d
8 2
c3
kBTd .
电磁场与电磁波英语缩写
Electromagnetic Fields and Electromagnetic Waves: An Exploration of Their Abbreviations In the vast and intricate realm of physics, electromagnetic fields and electromagnetic waves occupy a central and fundamental position. These phenomena, which underlie much of our modern technology, are often abbreviated for brevity and efficiency. Understanding these abbreviations not only aids in the comprehension of physics concepts but also facilitates communication among expertsin the field.The abbreviation "EMF" is commonly used to refer to electromagnetic fields. This abbreviation encapsulates the interaction between electric and magnetic fields, which together form a dynamic and pervasive force in nature. Electromagnetic fields are generated by charged particles and affect the behavior of other charged particles, creating a rich and complex tapestry of interactions.Electromagnetic waves, on the other hand, are often abbreviated as "EMW." These waves propagate through space at the speed of light, carrying energy and information. They are the basis for radio waves, microwaves, infraredradiation, visible light, ultraviolet radiation, X-rays, and gamma rays, among others. Each type of electromagnetic wave has unique properties and applications, ranging from wireless communication to medical imaging.The abbreviations "EMF" and "EMW" serve as shorthandfor complex and multifaceted concepts. However, it is important to note that these abbreviations should not be confused with each other. While both refer to electromagnetic phenomena, they describe distinct aspects of this vast and fascinating field.Electromagnetic fields (EMF) describe the interaction of electric and magnetic fields, while electromagnetic waves (EMW) refer to the propagation of energy and information through space. Understanding the distinction between these abbreviations is crucial for accurately communicating and comprehending electromagnetic phenomena. In conclusion, electromagnetic fields and electromagnetic waves are fundamental concepts in physics, with abbreviations "EMF" and "EMW" serving as shorthand for brevity and efficiency. Understanding these abbreviations and their respective meanings is essential forcomprehending the intricate and vast world of electromagnetic phenomena.**电磁场与电磁波：探索它们的缩写**在物理学的广阔而复杂的领域中，电磁场与电磁波占据着中心且基础的位置。
物理学专业英语讲义
Physics in EnglishThe scientist does not study nature because it is useful;he studies it because he delights in it,and he delights in it because it is beautiful.If nature were not beautiful,it would not be worth knowing,and if nature were not worth knowing,life would not be worth living."------ Henri PoincareDepartment of PhysicsSchool of scienceXian Technological University 2012.9Chapter 1 What is Physics?Physics is natural science studying nature's LawsPhysics was called natural philosophy and fundamental science.The history of physicsThe history of physics encompasses two broad time periods in which classical physics and modern physics developed. Classical physics developed between 1600 and 1900. It embraces the general areas of physics known as mechanics, thermodynamics, and electromagnetism, culminating in relativity. Modern physics began developing between about 1890 and 1930, when it was realized that classical physics could not account for the newly discovered behavior of nature at the atomic and molecular level. Modern physics includes the theory of relativity as well as quantum mechanics and most of the subsequent new physics discovered and developed during the 20th century.Classical physicsClassical physics includes the traditional branches and topics that were recognized and well-developed before the beginning of the 20th century—classical mechanics, optics, thermodynamics, and electromagnetism. Classical mechanics is concerned with bodies acted on by forces and bodies in motion and may be divided into statics (study of the forces on a body or bodies at rest), kinematics (study of motion without regard to its causes), and dynamics (study of motion and the forces that affect it); Acoustics, the study of sound, is often considered a branch of mechanics because sound is due to the motions of the particles of air or other medium through which sound waves can travel and thus can be explained in terms of the laws of mechanics. Among the important modern branches of acoustics is ultrasonics, the study of sound waves of very high frequency beyond the range of human hearing. Optics, the study of light, is concerned not only with visible light but also with infrared and ultraviolet radiation, which exhibit all of the phenomena of visible light except visibility, e.g., reflection, refraction, interference, diffraction, dispersion, and polarization of light. Heat is a form of energy, the internal energy possessed by the particles of which a substance is composed; thermodynamics deals with the relationships between heat and other forms of energy. Electricity and magnetism have been studied as a single branch of physics since the intimate connection between them was discovered in the early 19th century; an electric current gives rise to a magnetic field and a changing magnetic field induces an electric current. Electrostatics deals with electric charges at rest, electrodynamics with moving charges, and magnetostatics with magnetic poles at restThe Emergence of Classical PhysicsClassical mechanics has its roots in the work of Johannes Kepler, who, between 1600 and 1619, became the first person to describe quantitatively and accurately the elliptic paths of the planets around the Sun.The problem of the shape of the planetary orbits was not easy to solve, because all historical observations of the planets were made from the Earth, itself a moving planet. Although a crude heliocentric(Sun-centered) model of the solar system using circular orbits was proposed by the Greek astronomer Aristarchus in the third century B.C. and resurrected by Copernicus in 1542,the planetary positions predicted by Copernicus were not as accurate as those found using Ptolemy's complicated geocentric (Earth-centered} model of the second century A.D.The pure Copernican model was inaccurate because Copernicus refused to abandon the flawed concept of early Greek thought that the natural path of a moving "perfect" celestial object, such as a planet, had to be in the shape of the "perfect" geometrical figure---a circle---with the planet moving at constant speed. a scientist living at the time of Copernicus would have been forced to reject the Copernican theory with its circular planetary orbits, since they did not account for the observed motions of the planets as accurately as the existing, but more complicated, geocentric theory of Ptolemy.The change from the accurate but complex Ptolemaic geocentric model of the solar system to the accurate and simple heliocentric model of Kepler illustrates the characteristics of a good theory. With Kepler's work, accuracy and simplicity blossomed simultaneously from the heliocentric hypothesis. Kepler's model and mathematical methods began the development of physics as we know it. His work was a watershed of quantitative thought and a new worldview.Observation of nature and experimental results typically precede the general theories that account for them. The extensive observations of the planets by Tycho Brahe just prior to 1600 provided Kepler with the data he needed to model the solar system accurately and precisely。
物理电学完整知识点
物理电学完整知识点物理电学是物理学中研究电荷、电场、电流、电压、电阻、电容、电感以及电磁现象的分支。
以下是物理电学的完整知识点概述：1. 电荷（Charge）- 基本粒子的属性，分为正电荷和负电荷。
- 电荷守恒定律：在一个封闭系统中，总电荷量保持不变。
2. 电场（Electric Field）- 电荷周围存在的一种力场，可以对其他电荷施加力。
- 电场强度（E）：单位正电荷在电场中受到的力。
- 电场线：表示电场方向和强度的虚拟线条。
3. 电势（Electric Potential）- 电荷在电场中具有的势能，与电场强度和距离有关。
- 电势差（Voltage, V）：两点间的电势能差。
4. 电流（Electric Current, I）- 电荷的流动，单位时间内通过导体横截面的电荷量。
- 电流的方向：正电荷移动的方向。
5. 电阻（Resistance, R）- 导体对电流的阻碍作用，与材料的性质、温度、长度和截面积有关。
- 欧姆定律：V = IR，电压与电流和电阻成正比。
6. 电容（Capacitance, C）- 存储电荷的能力，与两个导体板的面积、板间距和介电常数有关。
- 充电和放电过程：电容器在充电时存储能量，在放电时释放能量。
7. 电感（Inductance, L）- 线圈对电流变化的抵抗能力，与线圈的匝数、面积和材料有关。
- 感应电动势：当电流通过线圈时，会在其周围产生变化的磁场，从而在线圈中产生感应电动势。
8. 电磁感应（Electromagnetic Induction）- 变化的磁场可以在导体中产生电动势。
- 法拉第电磁感应定律和楞次定律描述了电磁感应的基本原理。
9. 电路（Circuit）- 由电源、导线、电阻、电容、电感等元件组成的闭合路径。
- 串联和并联电路：元件连接的方式影响电流和电压的分布。
10. 直流电（DC）与交流电（AC）- 直流电：电流方向和大小不随时间变化。
- 交流电：电流方向和大小随时间周期性变化。
电磁学Electromagnetics教学课件
电磁学的发展历程
19世纪初，英国物理学家迈克尔·法 拉第发现了电磁感应定律，奠定了发 电机的理论基础。
1887年，德国物理学家海因里希·鲁 特通过实验证实了电磁波的存在，奠 定了无线通信的基础。
1860年代，詹姆斯·克拉克·麦克斯韦 提出了麦克斯韦方程组，统一了电场 和磁场，预言了电磁波的存在。
磁场强度是描述磁场中某点磁体所受作用力的物理量，与磁场 力和磁体磁矩成正比，与距离平方成反比。
静磁场是指静止磁体和恒定电流产生的磁场，其特点是磁体和 电流分布不随时间变化。
电荷与电流
电荷概念
电荷是物质的基本粒子，具 有正负两种电荷。同种电荷 相互排斥，异种电荷相互吸 引。
电流
电流是单位时间内通过导体 横截面的电荷量，其大小与 电压和电阻成正比。
电磁力与物质相互作用实验
总结词
探究电磁力与物质的相互作用规律
详细描述
通过实验了解电磁力与物质的相互作用规律 ，掌握电磁感应、电磁力的测量方法，了解 电磁力在生产和生活中的应用，如电动机、 发电机等。
THANKS
感谢观看
图像信息。
磁悬浮列车
总结词
磁悬浮列车是一种新型交通工具，利用电磁原理实现列车与轨道的无接触悬浮和导向。
详细描述
磁悬浮列车通过强大的电磁场产生吸引力或排斥力，使列车与轨道之间保持一定距离，实现列车的高 速运行。磁悬浮列车具有无摩擦、低噪音、低能耗等优点，是未来交通工具的发展方向之一。
07
CATALOGUE
电场强度
电场强度是描述电场中某点电荷所受作用力的物理量，与电场力和电 荷量成正比，与距离平方成反比。
Electromagnetic radiation
c=λf c：波速(光速是一个常量，真空中约等于3×108m/s) 单位： m/s f：频率（单位：Hz,1MHz=1000kHz=1×106Hz） λ：波长（单位：m） 真空中电磁波的波速为c，它等于波长λ和频率f的乘积 c=λf 真空中电磁波传播的速度c—大约30万千米每秒，是宇宙间 物质运动的最快速度。c是物理学中一个十分重要的常数， 目前公认的数值是： c=299792.458km/s≈3×108m/s
• 无线电波3000米～0.3毫米。（微波0.1~100厘米） • 红外线0.3毫米～0.75微米。（其中：近红外为0.76~3微米，中红外为 3~6微米，远红外为6~15微米，超远红外为15~300微米） • 可见光0.7微米～0.4微米。 • 紫外线0.4微米～10纳米 • X射线10纳米～0.1纳米 • γ射线0.1纳米～1皮米 • 高能射线小于1皮米 • 传真（电视）用的波长是3～6米；雷达用的波长更短，3米到几毫米。
Hale Waihona Puke photons 光子• 光量子，简称光子（photon），是传递电磁相互作用的基本粒子， 是一种规范玻色子。光子是电磁辐射的载体，而在量子场论中光 子被认为是电磁相互作用的媒介子。 • 爱因斯坦（A.Einstein）提出，为了解释光电效应（photoelectric effect）。
光子的能量 • E=hf 1. E（energy）：光子的能量 2. F（frequency）：电磁波得到频率 3. h（planck’s constant）：6.63*10^-34JS • C=f λ
Electromagnetic radiation
电磁辐射
电磁波（Electromagnetic waves）是由 同相振荡且互相垂直的电场与磁场在空间中以波的 形式移动，其传播方向垂直于电场与磁场构成的平 面，有效的传递能量和动量。 电磁辐射（Electromagnetic radiation） 可以按照频率分类，从低频率到高频率，包括有无 线电波、微波、红外线、可见光、紫外线、X射线和 伽马射线等等。人眼可接收到的电磁辐射，波长大 约在380至780纳米之间，称为可见光。只要是本身 温度大于绝对零度的物体，都可以发射电磁辐射， 而世界上并不存在温度等于或低于绝对零度的物体。 电磁波向空中发射或泄露的现象，叫电磁辐射。
ElectromagneticWaves.ppt
This page was copied from Nick Strobel's Astronomy Notes. Go to his site at for the updated and corrected version.
A changing magnetic field creates a changing electric field.
One example of this is a transformer which transfers electric energy from one circuit to another circuit.
What happens when electric and magnetic fields change?
A changing magnetic field creates a changing electric field.
What happens when electric and magnetic fields change?
What happens when electric and
magnetic fields change?
A changing magnetic field creates a changing electric field.
One example of this is a transformer which transfers electric energy from one circuit to another circuit.
What are electromagnetic waves?
How electromagnetic waves are formed How electric charges produce
电磁场与电磁波课程教学大纲
《电磁场与电磁波》课程教学大纲一、课程基本信息课程代码：课程名称：电磁场与电磁波英文名称：Electromagnetic Fields and Electromagnetic Waves课程类别：专业基础课学时：63学分：3适用对象: 电子信息专业考核方式：考试先修课程：大学物理、高等数学与工程数学(包括矢量分析,场论和数理方程等)二、课程简介电磁场与电磁波是通信技术的理论基础，是电子信息专业本科学生的知识结构中重要组成部分。
本课程使学生掌握电磁场的有关定理、定律、麦克斯韦方程等的物理意义及数学表达式。
使学生熟悉一些重要的电磁场问题的数学模型（如波动方程、拉氏方程等）的建立过程以及分析方法。
培养学生正确的思维方法和分析问题的能力，使学生学会用"场"的观点去观察、分析和计算一些简单、典型的场的问题。
为后续课程打下坚实的理论基础。
Electromagnetic Field and Electromagnetic Wave is the theoretical foundation of communication technology, it is one of the most important components of the knowledge structerue for undergraduate students who major in information and electronic. Electromagnetic Field and Electromagnetic Wave make students grasp the theorem and the physical meaning of the Maxwell equations and mathematical expressions. It also make students grasp building method and analyzing method of some important mathematical model (such as wave equation,Laplace equation). This course trains students on the proper ways of thinking and ability to analyze issues, It also provides a solid theoretical foundation for following courses.三、课程性质与教学目的一切电现象，都会产生电磁场，而电磁波的辐射与传播规律，更是一切无线电活动的基础。
电磁波 核磁共振
电磁波和核磁共振（Nuclear Magnetic Resonance，简称NMR）是物理学和化学领域中的两个重要概念，它们之间有一定的关联。
1. 电磁波（Electromagnetic Waves）：
- 电磁波是由电场和磁场相互耦合而产生的波动现象。
它们是一种无质量的能量传播方式，可以在真空中传播，速度等于光速。
- 电磁波的典型例子包括可见光、无线电波、微波、红外线、紫外线、X射线和γ射线等。
- 电磁波具有不同的波长和频率，可以用于许多应用，包括通信、成像、加热和科学研究等。
2. 核磁共振（Nuclear Magnetic Resonance，NMR）：
- 核磁共振是一种用于分析样本中核自旋的技术。
它广泛应用于化学、生物化学、药物研发和医学等领域。
- 在NMR中，样本放置在强磁场中，核自旋（通常是氢、碳、氮等核子的自旋）会在特定的频率下共振。
通过测量核自旋的共振频率和强度，可以获得关于样本的结构和组成信息。
- NMR可以用于确定化合物的结构、跟踪反应动力学、研究生物分子的结构和相互作用等。
虽然电磁波是一种广泛的物理现象，但核磁共振是一种特定的实验技术，利用核子的磁性来获得有关样本的信息。
在NMR实验中，尤其是在高分辨率NMR中，使用射频脉冲来操纵和观察核自旋的行为。
这种技术的核心是核磁共振现象，涉及到核子在外加磁场下的共振吸收和发射。
因此，虽然电磁波广泛存在于自然界中，但在核磁共振中，我们特别关注核自旋与电磁波之间的相互作用，以从中获得有关样本的信息。
物理22章知识点总结
物理22章知识点总结22.1 电子衍射22.1.1 电子衍射的实验现象电子衍射是指当高速电子穿过晶体或金属薄膜时，会发生衍射现象，表现出干涉条纹的特点。
22.1.2 德布罗意波长德布罗意波长是指用来描述粒子的波动性质的物理量，可以通过德布罗意关系来计算，表达式为λ=h/p，其中λ为德布罗意波长，h为普朗克常量，p为粒子的动量。
22.1.3 配合滤镜配合滤镜是指用来改变电子的能量和波长，从而探测不同物质的衍射图样，通过调节配合滤镜的电压，可以控制电子的能量，进而改变其德布罗意波长。
22.2 光子的波粒二象性22.2.1 光的波粒二象性光既可以表现出波动性，又可以表现出粒子性。
在实验中，光的波动性可以由干涉和衍射来解释，而光的粒子性可以由光电效应和康普顿散射来解释。
22.2.2 波长和频率光的波长和频率之间有着紧密的关系，可以通过光速等于波长乘以频率来表示。
22.2.3 光子的动量和能量光子的动量和能量与其波长和频率之间有着一定的关系，可以通过光子动量公式和光子能量公式来计算。
22.2.4 波包与波束波包是指由不同波长的波构成的波动现象，而波束是一组处于相干状态的波所组成的集合，可以在物理实验中观察到波束的干涉和衍射现象。
22.3 康普顿效应22.3.1 康普顿效应的实验现象康普顿效应是指当X射线与物质相互作用时，X射线会散射出不同波长和动量的光子，导致散射光的能量和波长发生改变。
22.3.2 康普顿公式康普顿公式可以通过光子的波粒二象性来解释，用来描述康普顿效应中散射光的波长和入射光的波长之间的关系，表达式为λ'-λ=h/mc(1-cosθ)，其中λ'为散射光的波长，λ为入射光的波长，h为普朗克常量，m为光子的静止质量，c为光速，θ为散射角。
22.3.3 康普顿散射的能量守恒和动量守恒在康普顿散射中，能量守恒和动量守恒是两个重要的物理定律，能够用来解释散射光的能量和动量之间的关系。
遥感物理基础电磁波基础物体的发射辐射PPT精品
地物光谱发射特 性曲线
地物在不同波段上 光谱发射率不同， 波长与发射率的对 应关系绘制而成的 曲线即为地物光谱 发射特性曲线。
The emission of ground object
Type
1. 原子光谱——核外电子能级跃迁； 2. 分子光谱——跃迁、振动及转动； 3. 晶体光谱——包括晶体振动。
晶体振动 3 ~ 30m
中红外、远红外
Definition
电磁波谱：按电磁波在真空中传播的波长或频率， 递增或递减排列，则构成电磁波谱。
电磁波的分类及其在遥感中的应用
电磁波分类 Υ射线 [小于10-6μm]
面积的辐射能 • 辐射通量密度（E=dΦ/ds）：单位时间通过单
位面积的辐射能
Measurement of electromagnetic radiation
辐照度(irradiation) （I=dΦ/ds）：被辐射物 体表面单位面积上的辐 射通量
辐射出射度(radiant exitance) （M=dΦ/ds）： 辐射源物体表面单位面 积上的辐射通量
按照发射率与波长的关系， 把地物分为： 1）黑体：发射率=1 2）灰体(grey body)：发射 率<1，常数 3）选择性辐射体(Selective radiator)：发射率<1，且随 波长而变化。
不同类型地物的发射率
影响地物发射率的因素：
地物的性质、表面状况、温度：比热大、 热惯量大，以及具有保温作用的地物， 一般发射率大，反之发射率就小。一般 常用平均发射率来表示地物的发射能力。
对普朗克公式微分求极值：