In 1831, British scientist Michael Faraday (1791-1867)
discovered the
phenomenon of electromagnetic induction and put forth the law of electromagnetic induction, which states that a time-varying magnetic field must give rise to an electric field. 1831 年英国科学家法拉第（ 1791 － 1867 ）发现电磁感应现象，创建了电
Investigation on the relation between the field and its source is a fundamental subject. We will introduce a number of mathematical equations to describe the relationship between the field and the source, as well as between the field and the media.研究场与源的关系是电磁理论的基本问题之一。我们
Class hour distribution
（Class hours 64：Lecture 60，Spare:4）
Vector analysis 4 Electrostatic fields 7 Boundary-value problems 4
EM induction 3 Time-varying EM fields 7 Plane EM waves 10 Guided EM waves 8
which will modify the original field distribution.
between the field and matters.
This is the interaction
当空间存在媒质时，在电磁场的作用下媒质中会发生极化与磁化现象，
结果在媒质中又产生二次电场及磁场，从而改变了媒质中原先的场分布，这
电磁场。
Field & Source 场与源
Electric charges and currents are the only sources for producing electromagnetic fields. Up to now, no magnetic charge or magnetic current has been found to exist in nature.电荷及电流是产生电磁场惟一的源。至今，人们 尚未发现自然界中存在磁荷及磁流。 Nevertheless, the introduction of magnetic charges and currents in the analysis of electromagnetic fields can prove to be beneficial sometimes, although these must be treated as fictitious entities.然而，有时引入磁荷及磁 流的概念是十分有益的，但是，它们仅是假想的。
In 1820, Danish scientist Hans Christian Oersted (1777—1851) discovered the magnetic field produced by an electric current. In the same year, French scientist Andre Marie Ampere安德烈.玛丽.安培(1775—1836) determined the force between two electric currents. 1820 年丹麦人奥斯特（ 1777 － 1851 ）发现了电流产生的磁场，同年法国 科学家安培（1775－1836）计算了两个电流之间的作用力。
磁感应定律，说明时变磁场可以产生时变电场。
A Great Innovation 重大突破
In 1873, British scientist James Clerk Maxwell (1831—1879) postulated the displacement current, which provided the link between a time-varying electric field and a magnetic field. He put on a firm mathematical foundation the laws governing an electromagnetic field. They are known today as the famous Maxwell’s equations. 1873年英国科学家麦克斯韦（1831－1879）提出了位移 电流的假设，认为时变电场可以产生时变磁场，并以严格数学方程描述了电 磁场与波应该遵循的统一规律，这就是著名的麦克斯韦方程。
Forces and energy are the most important.
The existence and transmission of electromagnetic waves need not rely on any medium. Specifically, when an electromagnetic wave travels through a vacuum, it is said to propagate in “free space”. 电磁场与电磁波是一种物质，它的存在和传播无需依赖于任何媒质。在 没有物质存在的真空环境中，电磁场与电磁波的存在和传播会感到更加“自
Electromagnetic Fields and Waves
Rugui Yang
Higher Education Press
Higher Education Electronic and Video Press
The physical understanding is emphasized instead of the mathematical derivation.
Steady current fields 3
Steady magnetic fields 6
Principles of EM radiation 8
Preface 前言
Electric Field & Magnetic Field 电场和磁场
The fields produced by the static charges behaves as the function of the force acting on the charge, and it is called the electric fields. 静止电荷产生的场表现为对于带电体有力的作用，这种场称为电场 The electricfields unchanging with time are called electrostatic fields. 不随 时间变化的电场称为静电场 The fields produced by the moving charges or the electric currents behaves as the function of the force acting on the magnet and the conductor carrying currents are called magnetic fields. 运动电荷或电流产生的场表现为对于磁铁和载流导体有力的作用，这种物质 称为磁场 The magnetic fields unchanging with time are called steady magnetic fields. 不随时间变化的磁场称为恒定磁场。
and may be investigated separately.静电场与恒定磁场相互无关、彼此独立， 可以分别进行研究EnFra bibliotekity 物质属性
Electromagnetic fields and waves are invisible (except for visible light), their existence can be inferred from the energy and momentum they carry. 电磁场与电磁波虽然不能亲眼所见，但是客观存在的一种物质，因为它 具有物质的两种重要属性：能量和质量。但是，电磁场与电磁波的质量极其 微小，因此，通常仅研究电磁场与电磁波的能量特性。
就是场与媒质的相互作用现象。 For the convenience of study, we first introduce electro-magnetic fields in free space, after which the electromagnetic field in matter will be discussed. 为了研究方便起见，我们先介绍真空中的电磁场，然后再讨论媒质中的
将要详述场与源，以及场与媒质之间的关系，并且给予严格的数学描述。
History 历史的回顾
The ability of a piece of amber琥珀 to attract small items after it had been rubbed was discovered by the Greeks in 600 B.C. The attractive force between a magnet and iron铁 was noted by the Chinese in 300 B.C. 公元前600年希腊人发 现了摩擦后的琥珀能够吸引微小物体；公元前 300年我国发现了磁石吸铁的现 象； Early in the first century, the compass was invented and it was among the four great inventions in ancient China. Thereafter, the magnetic field of the earth was discovered. In 1785, French scientist Charles Augustin de Coulomb (1736—1806) discovered Coulomb’s law (1785年法国科学家库仑（1736－1806）通过实验 创建了著名的库仑定律 ), and it gives the relationship between the force experienced by two small charged objects and the distance between them.