Why does a moving electric charge produce a magnetic field?do photons create gravitational field?

Question

Why does a moving electric charge produce a magnetic field?do photons create gravitational field?

Answer 1

Most of the times it is considered a known fact, but it does have an explanation. To understand this concept you should have some knowledge about relativity, Lorentz factor and length contraction. I have tried to explain it below in simplest possible way:



For a static charged particle, you can consider an imaginary sphere where the electric field is constant, but when the charged particle is moving say towards right, the imaginary sphere will contract to an ovular shape due to length contraction. Therefore the field still points directly away from the point charge, but it's not the same in all directions taken along the sphere, it's weaker in front of and behind the particle, and stronger to the sides.



As for photons, only its rest mass is zero, otherwise it posses mass and momentum and yes they are affected by gravity as in black hole. i have also read somewhere that a/c to general theory of relativity gravity is stress energy tensor. By virtue of momentum some components of stress energy tensor are non zero , so it can also act as a source of gravity. Also the concept of geodesics and mass wraps space and in turn time also gives a hint of explanation.

Answer 2

No, photons do not create a gravitational field.



As for why moving charges produce a magnetic field, there is no "reason" for this--it's just a law that they do.



Here's a more interesting question:



You have two observers. One is standing still and watches a charged particle fly by. Since he knows moving charged particles create a magnetic field, he predicts what the magnetic field will be (and is correct). The other observer moves with the charged particle--so to him, the charged particle is stationary. So does the moving observer predict and/or measure a magnetic field?





Edit:



@Andrew Smith: General Relativity explains why light can have no mass and yet still be affected by gravity. This is because mass warps space time, therefore light is merely traveling along geodesics (shortest paths). For flat space this would be in perfectly straight lines, however, if space is curved (due to mass warping it), then it will appear to curve or bend. This is consistent with the idea that photons have no mass yet are still affected by gravity.



Furthermore, special relativity, shows that mathematically, the only possibly way for something to travel at the "speed of light" is if it has no mass. I will offer a caveat though, which is that if light has, perhaps a TINY bit of mass, it still might be possible to go at say, 99.9999999999999% of the speed of light, which perhaps we cannot measure the difference (which might be a bit circular anyway--since we define the speed of light as the speed at which photons travel to begin with).

Answer 3

No one will ever know WHY. not really for anything.

All arguments become circular. Relating one property to other properties so the answer for why can always be challenged with a further why.



You don't seem to appreciate what science is all about.

We use our explanations about processes ( theories ) to predict what will occur.

While they make good predictions then they remain useful theories but no one ever imagines that they represent the absolute unchallengable truth.





Now for photons. Light is affected by gravity. Yet gravity is symmetric. F = GMm/ R^2

and as every action has an equal and opposite reaction then if light is affected BY gravity then light must also POSSES a small amount of gravity.



As a photon is so light it is most unlikely that we will be able to test this by the use of two photons to see if they attract each other.

So this is only a theoretical extrapolation.



Note that there can be many ways of explaining a situation. All of which make valid explanations.

Some say that light has NO mass therefore it cannot have any gravity.

But then there needs to be other fudges to explain why it is affected by gravity.

I am not satisfied that this is the most profitable way to view the situation.

Answer 4

The fact that moving charged particles produce a magnetic discipline and that magnetic feild is perpendicular to the direction of movement are simply houses of all charged particles, its simply there. Like the drive on a physique is mass occasions acceleration. They're just physical houses of matter, and we use math to place statement correctly into the units that we build. The magnetic area is just a drive subject like electrical field and gravitational subject and so on. You are not able to relatively see them however the fields are simply a great way of representing the consequences of electromagnetism and gravitation and many others.

Answer 5

Photons dont have any charges