Electromagnetic radiation effect on electric field?

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Hi, just trying to better understand this concept of electromagnetic radiation.

My understanding thus far is that it is a traveling disturbance in the electric field. This picture here seems to help me see what is happening:

https://en.wikipedia.org/wiki/Electromagnetic_radiation#/media/File:Electromagneticwave3D.gif

My understanding of the electric field thus far is that at any given point in space, there is a magnitude and direction which will determine the force acting on a charged particle at that point. That magnitude in direction is computed as the sum of all contributions from other nearby particles (I guess either protons or electrons), based on their sign +/- and their position wrt to that point. Often I've seen the electric field be represented as this grid of pointing vectors. All that I think makes sense to me.

Anyway, back to my question. So what does this traveling disturbance through this grid of pointing vectors actually do? Does it affect both the magnitude and direction of the vectors? That gif I linked just shows a wave propagating, it doesn't show how it affects the electric field. Since each point on the electric field has both a direction and a magnitude, there are 2 things it could affect. My guess right now is that it just affects the magnitude of the electric field vectors, but it does it change their direction also?
 

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  • #2
BvU
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What you see in the gif IS the electromagnetic field. The blue guys are the B field and the red guys are the E field. They are completely connected with each other through the Maxwell equations. If - from e.g. a fixed charge in the neighborhood - there is a static electric field you can simply add up the vectors from that field and the E vector of the passing electromagnetic wave.
 
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  • #3
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Thanks for the reply, would the following description be accurate? Electromagnetic radiation is just a by-product of oscillating a charged particle. That is, when you move a charge, it changes the electric field, but that change in the electric field propagates outward from the charge at the speed of light, it doesn't change every point on the electric field immediately. If you move the charge up and down, this creates a wave pattern.

Is the gif I linked basically doing the exact same effect as this simulation, when you press the "sinusoidal" button?

https://phet.colorado.edu/sims/radiating-charge/radiating-charge_en.html
 
  • #4
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Thanks for the reply, would the following description be accurate? Electromagnetic radiation is just a by-product of oscillating a charged particle.
It isn't that simple because light comes in discreet packets of energy called photons. Some great physicists noted that if light was simply created by oscillating charges then electrons in orbit around atoms would constantly lose their energy and fall inward. Charged particles are small things so they are governed by quantum phenomena. On large scale, yes you can create a disturbance in the electric field or magnetic field and it will propagate as a wave through space. Essentially that's an antenna.
 
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Jonathan Scott
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My guess right now is that it just affects the magnitude of the electric field vectors, but it does it change their direction also?
The sum of two or more solutions is also a solution, and one simple way this can vary is known as polarization. There are for example specific polarized combinations which appear to rotate left or right. If two linearly polarized waves (as in the original gif) have the same frequency but their field vectors are oriented in different directions relative to the direction of travel and are out of phase, then the components of the field vector can trace an ellipse or a circle about the line of travel. One can alternatively consider a linearly polarized wave to be mathematically a sum of equal left and right circularly polarized waves.
 

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