# Magnetic field moving faster than speed of light?

• djsourabh
In summary: The power output of the radiation is related to the rate of change of the dipole moment (angular acceleration of the rotating magnetic dipole), which in turn is related to the jerk of the motion of the charges.In summary, the conversation discusses the possibility of a rotating magnetic field moving faster than the speed of light and the resulting phenomenon of radiation. It also addresses the fallacy of speaking about a "moving" electromagnetic field and the idea of the field pattern moving faster than the speed of light. The concept of the scissors paradox is also mentioned.
djsourabh
Magnetic field moving faster than speed of light?

We know the equations for speed of rotating magnetic field, as N= 120*f/P, where f is frequency of AC currents & P is number of magnetic poles.
Say by some method we are able to produce a very high frequency AC voltage & apply that to a stator of 3 phase induction motor's stator, such that the peripheral speed(v) of magnetic field (v=r*w; where r is radius of rotating magnetic field & w is angular speed (rad/sec) = 2*pi* N/60), exceeds 'c', the old speed of light. But according to special Relativity as we know this would not be possible. So what phenomenon would occur at that time? Does the radius of motor goes on decreasing as we increase the frequency?

djsourabh said:
We know the equations for speed of rotating magnetic field, as N= 120*f/P, where f is frequency of AC currents & P is number of magnetic poles.
Say by some method we are able to produce a very high frequency AC voltage & apply that to a stator of 3 phase induction motor's stator, such that the peripheral speed(v) of magnetic field (v=r*w; where r is radius of rotating magnetic field & w is angular speed (rad/sec) = 2*pi* N/60), exceeds 'c', the old speed of light. But according to special Relativity as we know this would not be possible.
It's a fallacy to speak about a "moving" electromagnetic field. Electromagnetic fields do not move, rather they sit in one place and vary with time. E.g. for a plane wave, the E and B fields do not travel along at the speed of light, they just sit still and vary! For the field of a rotating magnetic dipole, it's the field pattern that is seen to rotate, not the field itself. And the fact that this pattern may move faster than c is the old scissors paradox, where the intersection of the blades seems to move faster than c.

djsourabh said:
So what phenomenon would occur at that time? Does the radius of motor goes on decreasing as we increase the frequency?
Radiation. A rotating magnetic dipole radiates, and the pattern of the far field is different because of this.

nsaspook and djsourabh

## 1. Can a magnetic field really move faster than the speed of light?

According to the theory of relativity, the speed of light is considered to be the universal speed limit. This means that nothing can travel faster than the speed of light. Therefore, a magnetic field cannot move faster than the speed of light.

## 2. What happens if a magnetic field exceeds the speed of light?

If a magnetic field were to somehow exceed the speed of light, it would violate the laws of physics as we know them. This would have significant consequences for our understanding of the universe and could potentially lead to the breakdown of many scientific principles.

## 3. Are there any exceptions to the speed limit imposed by the speed of light?

Currently, there are no known exceptions to the speed limit imposed by the speed of light. However, there are some theoretical concepts, such as wormholes, that have been proposed as potential methods for traveling faster than the speed of light. These ideas are still highly debated and have not been proven to be possible.

## 4. How is the speed of light related to electromagnetism and magnetic fields?

Electromagnetism is one of the fundamental forces of nature and is responsible for the creation and behavior of magnetic fields. The speed of light is also closely related to electromagnetism, as it is the maximum speed at which electromagnetic waves can travel through a vacuum. This means that the speed of light is also the speed at which changes in magnetic fields propagate.

## 5. What are some practical applications of understanding the limitations of magnetic fields and the speed of light?

Understanding the limitations of magnetic fields and the speed of light is crucial in many fields of science and technology. It allows us to accurately model and predict the behavior of electric and magnetic fields, which is essential in the development of technologies such as electric motors, generators, and magnetic resonance imaging (MRI) machines. It also plays a crucial role in our understanding of the behavior of celestial objects and the universe as a whole.

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