为什么电场和磁场在电磁波中垂直?Why are electric and magnetic fields perpendicular in an electromagnetic wave?

【翻译自Quora】

@ Omkar Joshi, Physics,I like to understand the fundamentals. 的回答

It is very much interesting!

First, I will highlight the doubts which come to mind while thinking about EM waves.

首先,我要重点介绍谈到电磁波时的疑惑:

  • A accelerating charged particle generates EM wave. So why the charge must be accelerating and not at rest or moving with constant velocity?
  • 加速的带电粒子会产生EM波。 那么,为什么电荷必须加速而不是静止或以恒定速度运动?
  • Accelerating charged particle generates electric and magnetic field. What is electric and magnetic field?
  • 加速带电粒子会产生电场和磁场。 什么是电场和磁场?
  • The generated fields are perpendicular to each other. Why the generated fields are perpendicular to each other?
  • 生成的场彼此垂直。 为什么生成的场彼此垂直?
  • Why wave propagation looks like this? And how is the wave actually moving forward?
  • 为什么波传播看起来像这样? 浪潮实际上是如何前进的?
  • Do the EF and MF really generate each other?
  • EF和MF是否真的相互产生的?
  • For first question, if there is a static charge,the field generated is constant. Same is the case with constant velocity charge. The field generated in above two cases brings the test charges/dipoles to an equilibrium eventually after a short while from initiation. What does it mean? This means that the EM WAVE does not have its WAVEproperties of oscillation.Also it does not result in radiation absorption by a small length conductor.
  • 对于第一个问题,如果有静电荷,则产生的场是恒定的。 恒速充电也是如此。 在以上两种情况下产生的磁场最终会使测试电荷/偶极子在引发后短短的一段时间内达到平衡。 这是什么意思? 这意味着EM 波就没有了震荡的波属性,无法被小长度的导体吸收。
  • For second and third question, in reality the Electric field and Magnetic field are NOT Different. They are different MANIFESTATION of the SAME FIELD.
  • 对于第二和第三个问题,实际上,电场和磁场并没有不同。 它们是同一领域的不同体现。
  • field is called an Electric field when it affects the Test Charge and tries to bring it to equilibrium. It can be in any direction / orientation.
  • 当一个电场影响测试电荷并试图使其平衡时,该电场称为电场。 它可以在任何方向/方向。
  • field is called an Magnetic field when it affects the Test Dipole (consisting of and +ve charge and -ve charge) and tries to bring the dipole to equilibrium. It can be in any direction / orientation.
  • 当磁场影响测试偶极子(由+ ve电荷和-ve电荷组成)并试图使偶极子达到平衡时,该磁场称为磁场。 它可以在任何方向/方向。
  • Now we take that Electric field’(as named by us) direction / orientation as areference. Then you know, by fleming’s left hand law, only the dipole in a plane perpendicular to field influencing the test charge (we named it electric field) will be forced into equilibrium BY THAT ELECTRIC FIELD (at first it was simply a field).So the NAME of that field in the PERPENDICULAR PLANE where it affects a magnetic dipole is called MAGNETIC FIELD.
  • 现在,我们以电场(由我们命名)的方向/方向作为参考。 然后您就会知道,根据弗莱明的左手定律,只有垂直于影响测试电荷的场(我们将其称为电场)的平面中的偶极子才会被该电场(起初只是一个场)强迫进入平衡状态。 垂直平面中影响磁偶极子的那个场的名称称为磁场。
  • So you can see that, the same field in different planes where it affects different quantities is called by different names. Thus the EF and MF are perpendicular to each other. So every refence EF plane has a corresponding MF plane perpendicular to it.
  • 因此,您可以看到,影响不同种类物质的东西的名字将会不同。 因此,EF和MF相互垂直。 因此,每个参考EF平面都有一个垂直于其的相应MF平面。
  • Interesting point: If there had been one more entity consisting of three interacting charges (say electron, proton and XX, a tripole) then the same field, EF, MF would have another name in the plane (with reference to EF) affecting that TRIPOLE. say TRIPOLE field, TF.
  • 有趣的一点:如果存在一个由三个相互作用的电荷组成的实体(例如电子,质子和XX,一个三极管),那么同一场EF,MF在平面上将有另一个名称(参考EF)影响该TRIPOLE 。 也就是三极管场,称为TF。
  • So this also answers the fifth question, the fields do not generate each other but are called different names in differnt planes.
  • 因此,这也回答了第五个问题,即场之间不会相互生成,但在不同的平面中会被称为不同的名称。
  • For the fourth question, consider an electron spinning around the nucleus. Here the changing direction , hence the tangential velocity, imparts acceleration the electron.
  • 对于第四个问题,请考虑围绕核旋转的电子。 在这里,变化的方向(即切向速度)使电子加速。

Let the wave under observation be moving towards the direction. When the electron is at right (near X) of proton, it asserts maximum force on a +ve test charge, hence the crest of transverse EM wave in ANY field(EF,MF). This force exertion extends till infinity (magnitude decreases inverse square proportion to distance) only to be altered (magnitude at a point) by changing position of electron.

让观察中的波在X方向移动。 当电子在质子的右边(在X附近)时,它将在+ ve测试电荷上施加最大作用力,因此在任何场(EF,MF)中都产生了横向EM波的波峰。 这种作用力一直延伸到无穷大(幅度随距离减小成反比),仅能通过改变电子的位置来改变(一点处的幅度)。

When electron is at left of nucleus the force is minimum and thus trough is observed. Rest conditions remain same as above.

当电子位于原子核的左侧时,力最小,因此观察到了波谷。 休息条件与上述相同。

When electron is above or below the proton (in Y direction), the field is at some intermediate value of max/min which is taken as reference zero value through out the science community.

当电子在质子上方或下方(在Y方向上)时,电场处于max / min的某个中间值,整个科学界将其视为参考零值。

If you have any further doubt, feel free to discuss in comments. Different views are welcome.

如果您还有其他疑问,请随时在评论中进行讨论。 欢迎不同的意见。

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