# Electric Field of an Electromagnetic Wave

• enridp
In summary, the electric field of an EM wave is just like the electric field of static charges, unless you look in a mirror.

#### enridp

Hello !
I have a very old doubt about Electromagnetic Waves, I hope somebody can help me.
Is the electric field of an EM wave really an Electric Field?
I mean, what is the difference between that E field and an Electric field produced by, for example, an electron?
If we have an EM wave, polarized, with a ver very low frequency, then in some point of the space we will see a constant Electric field? like if it was generated by a charged particle or body?

Thanks !
Enrique.

There are two sources of an electric field E; a) the gradient of a potential (times -1) from electric charges, like electrons or protons, and b) the Faraday's law of induction (also times -1) as a result of the time derivative of a magnetic field in an encircling loop. Aside from the fact that only one of these can be a DC field, the two electric fields are identical, unless you look in a mirror. In a mirror, the sign of electric charges are unchanged, so the electric field is the same. On the other hand, the right hand rule in Faraday induction, if applied to the mirror reflection, will change the sign of the electric field in the loop. So unless you look very carefully, there is no difference between the electric field from real charges or from the curl E equation (in Maxwell's equations).

To show that the Faraday induction field has the same effect on an electron as the electric field of static charges, study the physics of the betatron, invented by Professor Kerst at the University of Illinois in 1940 to accelerate electrons.

Bob S said:
To show that the Faraday induction field has the same effect on an electron as the electric field of static charges, study the physics of the betatron, invented by Professor Kerst at the University of Illinois in 1940 to accelerate electrons.

I think you mean the "Ausserordentlichhochgeschwindigkeitelektronenentwickelndenschwerarbeitsbeigollitron" thank you very much.

Yes. The name "betatron" (a reference to the beta particle, a fast electron) was chosen during a departmental contest. Other proposals were rheotron, inductron, and even Ausserordentlichhochgeschwindigkeitelektronenentwickelndenschwerarbeitsbeigollitron, supposedly German for "extraordinarily high-speed electron producing hard work by golly-tron.". Maybe there should be an acronym, similar to FLAK.

## 1. What is an electric field?

An electric field is a physical quantity that describes the strength and direction of the force experienced by an electrically charged particle. It is a fundamental concept in electromagnetism and plays a crucial role in understanding the behavior of electrically charged particles and their interactions with each other.

## 2. How is an electric field created?

An electric field is created by the presence of electric charges. These charges can be stationary, such as in the case of a charged object, or in motion, as in the case of an electric current. Whenever there is a difference in electric charge between two points in space, an electric field is present.

## 3. What is an electromagnetic wave?

An electromagnetic wave is a type of wave that is created by the oscillation of electric and magnetic fields. It is a form of energy that can travel through space without the need for a medium. These waves are responsible for carrying energy and information through the electromagnetic spectrum, including radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays.

## 4. How does an electric field contribute to the formation of an electromagnetic wave?

An electric field is an essential component of an electromagnetic wave. It is created by the oscillation of charged particles, such as electrons, in an antenna or other source. This oscillation creates changes in the electric field, which in turn creates changes in the magnetic field. These changing electric and magnetic fields then propagate through space, creating an electromagnetic wave.

## 5. What are the properties of an electric field in an electromagnetic wave?

The electric field in an electromagnetic wave is oscillating and perpendicular to the direction of propagation. It also has a specific frequency and wavelength, which determine the energy and color of the wave. The strength of the electric field is determined by the amplitude of the wave, and it decreases as the distance from the source increases. Finally, an electric field can be polarized, meaning that its direction of oscillation can be controlled by external factors such as filters or lenses.