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How EM waves are produced say by a capacitor of an LC circuit here if $E$ is increasing in upward direction?

My thoughts

Thought 1:-

If E is increasing E flux is increasing thus B field must be created by seen in counter clockwise direction from above. Earlier B field was zero now it is not thus B field has increase B flux is increasing thus an E filed is induced in all directions around the ring of B field and so on The problem is that the direction of propagation of wave here is opposite to the direction of E×B vector.

Thought 2'-

At an instant There is an electric field now if it is induced electric field then there must be a change in magnetic flux around thus there is a magnetic field. The magnetic field is in clockwise direction as seen from above.now if there is a magnetic field thus there is change in electric flux around the electric flux must be in upward direction around the magnetic field ring.The problem is here that the induction works the other way a changing electric flux through a region produces magnetic field as in the first thought but here we are saying that if there is electric field then there must be changing magnetic flux which would have produced it is it true. And if true wouldn't a constant electric field then would produce an EM wave. We can just assume that the initial electric field in capacitor is constant but still then according to thought 2 EM wave must be created.

If both these are wrong then please tell me how an EM wave is created

My thoughts on wave propagation

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  • $\begingroup$ In both your sketches the arrows have to point in interchanging directions: E up, B left, E down, B right, ... $\endgroup$ Dec 1, 2019 at 18:04
  • $\begingroup$ I've only took account That the electric field in the capacitor is increasing for now.the wave is not sinusoidal. $\endgroup$ Dec 2, 2019 at 1:20
  • $\begingroup$ The way we teach electromagnetism suggests that E- and B-fields are somehow primary and that em-waves are an emergent phenomenon. where one component somehow "creates" the other. This is not a good way to intuitively think about electromagnetism because which components we observe depends on the relative motion between the observer and the (sources of the) fields. A constant magnetic field can, indeed, look like having an electric field component in addition to a moving observer. The better way to think about it is that any em field that obeys Maxwell's equations is physically "valid". $\endgroup$ Jan 23 at 3:34

2 Answers 2

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please tell me how an EM wave is created

First about EM radiation. Charges under acceleration emit EM radiation. The emission happens perpendicular to the direction of acceleration. For example, the synchrotron radiation is around the tangent of the accelerator ring. Accelerating a charge upwards the photons get emitted horizontally (in 360° around the wire).

To get an EM wave you simply has to drive your wire with an alternating current. The current modulate the EM radiation to a sinusoidal wave. Much better of course is to use a open circuit.

enter image description here

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  • $\begingroup$ I just want to go deeper in the same explanation . See here this is a changing electric field say It changes from E=0 to E=E0 in time t now what happens due to changing magnetic field. Electric flux is changing thus there must be a magnetic field surrounding which wasn't there before thus magnetic flux has just changed which will produce a corresponding electric field in nearby region. BUT the problem in this is that the direction of the corresponding magnetic field vectors I'm getting is just opposite to the actual direction of magnetic field so that the wave could propagate outward (E×B) $\endgroup$ Dec 7, 2019 at 8:12
  • $\begingroup$ Accelerating electric charges produce electromagnetic fields. Accelerating magnetic fields produce electromagnetic fields. Even direct current which is constant velocity is actually electrons bouncing around and produces a weak elf(extremely low frequency field). Elf can even be produced by spinning a magnet on a drill $\endgroup$
    – ChemEng
    Mar 8, 2022 at 19:58
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    $\begingroup$ What is an "accelerating magnetic field"? What is the velocity of the field? $\endgroup$
    – nasu
    May 17, 2023 at 11:44
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creation of magnetic field waves

creation of electric field waves

Let us begin with a definition, because arguing things without definition may lead to confusion. An electromagnetic wave is defined as an energy wave that has a velocity in vacuum that coincides with the velocity of light in vacuum. According to this definition, gamma rays, X-rays, ultraviolet rays, visible light rays, infra red rays, radio waves, and gravitational waves are known electromagnetic waves. Microwaves, alpha rays, and beta rays are not em waves as per this definition. To produce electric field waves there should be a strain in electric fields, and to produce magnetic field waves there should be a strain in magnetic fields. If the voltage is increased in a resistance, two successive electrons in serial try to come closer because of voltage, and two electric fields of two electrons should repel each other. So, there is a strain in electric field as it is explained in second figure to produce electric field waves or light rays. If the current is increased in a conductor, two successive electrons in parallel try to come closer because of increased current, and two magnetic fields of moving electrons should repel each other. So, there is a strain in magnetic field, as it is explained in first figure. These are all only situations related with voltage and current in production of electric field waves and magnetic field waves. In practical situations one need not go for voltage and current. In a fire, electrons of two successive molecules may bring a strain in electric field and it may produce light (or electric field wave). When there is a flow of gases in sun, the moving electrons moving in parallel may bring a strain in magnetic field and it may produce radio waves (or magnetic field waves). I ask the questioner to assume the followings (for which a basic theory may be found in a book entitled “Planets and electromagnetic waves”). The followings are based on mathematical interpretations for solutions of Maxwell equations. (1) If current exceeds some limit (depending on source of production), then magnetic field waves are produced. These waves are called in general radio waves. (2) If voltage exceeds some limit (depending on source of production), then electric field waves are produced. These waves are called in general light waves. (3) If current exceeds the corresponding limit and the voltage also exceeds the corresponding limit then both magnetic field waves and electric field waves exist separately; not in combined form (that is, not as everyone gives a figure for em waves with two component waves). A peculiar situation for (3) is the Hertz’s experiment. It may also happen both types of waves may not produced, and only oscillations may happen when the limits are not reached.

P.S. When two self rotating neutron stars come closer, the magnetic fields of the stars are disturbed and energy waves are released from the magnetic fields. These waves are gravitational waves. Since they are from magnetic fields, they are of electromagnetic wave type. After 1.7 seconds collision happens. During this collision, gamma rays, X-rays, ultra-violet rays, visible light rays and infra red rays may be released. For example, the article https://doi.org/10.1007/s11467-019-0913-4 explains such a delay of 1.7 seconds. Microwaves mentioned above in the answer correspond only to microwaves generated in micro ovens.

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    $\begingroup$ This answer is wrong. Gravitational waves are not electromagnetic waves and microwaves are electromagnetic waves. $\endgroup$
    – Dale
    Mar 22, 2021 at 18:49

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