# Electromagnetic Waves: Static Charges & Relativity Predictions

• Fibo112
In summary, the conversation discusses the relationship between the electric fields of static and moving charges and the emission of electromagnetic waves when charges are accelerated. The question is raised about the behavior of the field in a static frame of reference and whether it extends indefinitely. It is suggested that this concept can be used to predict electromagnetic waves and the behavior of moving charges. However, it is noted that this approach requires consideration of both the electric and magnetic fields and the use of Maxwell's equations, but it can serve as a starting point for understanding the origin of electromagnetic radiation.
Fibo112
I have learned about the electric fields of static charges and those of moving charges. From what I gather(although I have not really learned the specifics) when charges are accelerated they emit electromagntic waves which are essentialy an electromagnetic field progagating through space.

My question is the following: Based on the rules I have learned it seems that if a charge is static in a frame of reference, then its field in that frame of reference will extend out indefinetly. So to someone in that frame, the charge will seem to exert the regular q1q2/r^2 radial force on other charges even if they are millions of light years away?

If yes then at the point in time when the person in the reference frame looks at the distant object and observes the radial force, the distant object has no knowledge of the electrons previous locations in the past x years(x beeing the distance in light years). Can one predict the electromagnetic waves produced by accelerating charges by using relativity arguments based on this?( And also predict the field of moving charges and the same with the magnetic field through similar arguments)

Fibo112 said:
Can one predict the electromagnetic waves produced by accelerating charges by using relativity arguments based on this?
Predict the waves emanating from the distant object, or from the static frame?

Fibo112 said:
the charge will seem to exert the regular q1q2/r^2 radial force on other charges even if they are millions of light years away?
Yes, in principle. In practice, the ##1/r^2## factor means that any great distance the field becomes much too small to detect.
Can one predict the electromagnetic waves produced by accelerating charges by using relativity arguments based on this?( And also predict the field of moving charges and the same with the magnetic field through similar arguments)
That line of thought is used in at least one undergraduate textbook (Purcell) to explain the origin of electromagnetic radiation. You have to consider the magnetic field together with the electric field and work through Maxwell's equations to get a complete (as opposed to hand-waving heuristic) explanation, but this is a reasonable start.

No relativity is needed, and in fact the history goes the other way: Einstein started with an open problem in classical electromagnetism to arrive at relativity - he introduced relativity in a paper entitled "On the electrodynamics of moving bodies".

## 1. What are electromagnetic waves?

Electromagnetic waves are a type of energy that travels through space. They are created by the movement of electrically charged particles and can travel through vacuum or matter.

## 2. How are static charges related to electromagnetic waves?

Static charges are caused by an imbalance of electrons on an object. When these charges move or change, they create electric and magnetic fields, which in turn generate electromagnetic waves.

## 3. What is the connection between relativity and electromagnetic waves?

According to Einstein's theory of relativity, the laws of physics are the same for all observers in uniform motion. This means that the speed of electromagnetic waves, also known as the speed of light, is constant for all observers regardless of their relative motion.

## 4. Can electromagnetic waves be harmful?

Electromagnetic waves can have both positive and negative effects on living organisms. Some forms of electromagnetic radiation, such as UV rays and X-rays, can be harmful in high doses, while others, like visible light and radio waves, are generally considered safe.

## 5. How are electromagnetic waves used in everyday life?

Electromagnetic waves have a wide range of applications in our daily lives. They are used in communication technologies like cell phones and WiFi, in medical imaging devices like MRI machines, and in household appliances like microwaves and televisions.

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