# Exploring the Physics of ElectroMagnetic Waves

• IntuitioN
In summary, the conversation discusses the properties of light as an electromagnetic wave, specifically its E and B fields. It also mentions the use of these fields in technology such as superconducting RF cavities and the difficulty of visualizing electromagnetic waves as they are three-dimensional vectors. The question at the end pertains to the oscillation of the electromagnetic field in the presence of three photons and the use of QFT.
IntuitioN
This may sound dumb but...

since light is classified as an electromagnetic wave, it has an E field and a B field. But doesn't this mean the E field will attract metal, and the B field will cause currents to flow?

And since E = F/c = V/m does that mean the emr has a "voltage" or a "force"?

IntuitioN said:
since light is classified as an electromagnetic wave, it has an E field and a B field. But doesn't this mean the E field will attract metal, and the B field will cause currents to flow?

I think you meant to put E and B the other way around in your question. But yes, it's true. Radio waves are electromagnetic waves just like light waves but with a longer wavelength and lower frequency, and we detect them by the electric currents that the oscillating E and B fields produce in an antenna.

Off the top of my head (haven't had enough coffee yet this morning), I can't think of any experiments that "directly" observe the E and B fields in light waves, but I wouldn't be surprised to learn that this has been done.

Er... we put 1.3 GHz RF in our cavity and we have wall current losses, etc. directly due to the E and B field of the RF. So yes, this is something that is very obvious to us. It is why the ILC announced that the technology to be used in their accelerator will be the superconducting RF cavities. The whole purpose IS to reduce wall losses and get higher accelerating gradients.

Zz.

I plotted z=cos(x)+cos(y) in following interwals: x-direction: ]-infiniti, +infiniti[
and y-direction: [-pi/2, +pi/2]. I got something like the picture in the attached file (the picture isn't really good (because we can only attache 100 kb in this forum).

Now, the problem is actionally this one:
I don't know how a three (x,y,z) dimensional electromagnetic oscillation in ground state (in free space) lookes like. Someone gave me a guess (marlon). So I thought of drawing one to look if I'm right. In vacuum there are many oscillation. So I picked one oscillation and plottet it. That's why the y-direction of the oscillation has a certain minimum (pi/2) and a maximum (pi/2) (Think of cos(pi/2)=0).

Is that the right imagine of such an oscillation in ground state?

I would be thankful if someone might answer this question.

#### Attachments

• oscillation_1.bmp
98.7 KB · Views: 625
Can somebody help?

The electric and magnetic fields are vectors, so you can't draw an electromagnetic wave as a simple surface plot or line plot.

Here's my attempt at an incomplete picture of a plane electromagnetic wave that travels parallel to the x-axis. It's a snapshot at one particular point in time. The red arrows indicate the magnitude and direction of E at various points in the xy-plane. The dashed blue lines indicate where E is zero.

You have to complete this picture, mentally, as follows:

1. Every point in the plane, not just the ones shown, has an arrow attached to it, with a magnitude and direction interpolating the pattern that I've sketched.

2. Fill the space above and below the plane of the "paper" with copies of this diagram, stacked one on top of another so that all points in the three-dimensional space have arrows attached to them. The dashed blue lines become planes perpendicular to the x-axis.

3. Make copies of all those diagrams and change the color of the arrows from red to (say) green. Rotate them 90 degrees around the x-axis so the arrows all point towards and away from you, and the y-axis points towards you (that is, it becomes the z-axis), and the x-axis is the same as the other x-axis. This is the magnetic field B that is associated with this wave. The planes where E is zero are also the planes where B is zero.

4. As time passes, the magnitudes and directions of the E and B vectors at each point oscillate in such a way that the overall pattern (but not the arrows themselves!) marches from left to right or from right to left at speed $c$. At all times, at each point, the red arrow points either up or down, or vanishes momentarily; and the green arrow points either towards or away from you, or vanishes momentarily.

#### Attachments

• Efield-fixed.gif
22 KB · Views: 711
Last edited:
@jtbell: You are right. But I speak about QFT and the oscillation of the electromagnetic field in present of for example 3 photons.

## 1. What are electromagnetic waves?

Electromagnetic waves are a type of energy that is made up of oscillating electric and magnetic fields. They are created by the movement of charged particles and can travel through a vacuum at the speed of light.

## 2. What is the electromagnetic spectrum?

The electromagnetic spectrum is a range of all possible frequencies of electromagnetic radiation. It includes radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays.

## 3. How do electromagnetic waves interact with matter?

Electromagnetic waves can interact with matter in several ways, depending on the frequency of the wave. They can be reflected, absorbed, or transmitted through a material. The interaction of electromagnetic waves with matter is the basis for many technologies, such as radios, cell phones, and medical imaging devices.

## 4. What is the difference between electromagnetic waves and sound waves?

The main difference between electromagnetic waves and sound waves is that electromagnetic waves can travel through a vacuum, while sound waves require a medium, such as air, to travel through. Additionally, electromagnetic waves are transverse waves, meaning that the oscillations are perpendicular to the direction of the wave, while sound waves are longitudinal waves, meaning that the oscillations are parallel to the direction of the wave.

## 5. What are some real-life applications of electromagnetic waves?

Electromagnetic waves have many practical applications in our daily lives. Some common examples include communication technologies like radio, television, and cell phones, as well as medical imaging technologies like X-rays and MRI machines. They are also used in cooking (microwaves) and security systems (infrared sensors).

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