special theory of relativity says;;;;;;an observer at rest with respect to a system of static free charges will see no magnetic field. however, a moving observer looking at the same set of charges does perceive a current and thus a magnetic field.
in a similar way does observer travelling with a speed of light perceive magnetic field?
An "observer" travelling with the speed of light (in vacuum) would not have the time to perceive anything!
@ Kåre Olaussen..
My dear Kåre Olaussen so what happens at that speed?
According to special relativity, you have two invariants E^2 - B^2= F and E\cdot B-= G. Assume you are in a constant magnetic field B (E =0) and moves fast parallel to B. You see also ONLY the magnetid field B, even at speeds appraching c. If you move nonparallel to B, you will see both electric and magnetic fields such that F and G remain invariant. E and B transform according to the structure of the electromagnetic field tensor, (see for instance Landau and Lifshitz, The Classical Theory of Fields)
@ Hugo Celso. Perez Rojas ,
my dear Hugo Celso. Perez Rojas , we know, According to special relativity, you have two invariants E^2 - B^2= F and E\cdot B-= G. Assume you are in a constant magnetic field B (E =0) and moves fast parallel to B. You see also ONLY the magnetid field B, even at speeds appraching c.
now can we see magnetic field exactly at 'c' ?
@Stam Nicolis
My dear Stam Nicolis I am asking a question Does observer travelling with a speed of light perceive magnetic field?
``perceive'' doesn't make sense. What does make sense is specifying the interaction. A photon can react-through quantum effects-with a magnetic field and, in a medium, can change its polarization, through Faraday rotation, through the usual interaction with the medium.
An observer cannot move at the velocity of light never. This was a worry of Einstein, what would happen for an observer on an electromagnetic wave? Let us to have one imaginary massless observer on the electromagnetic wave, he should see that a magnetic field were arising and disappearing substitud by a complementary electric field. The curious is that this observer cannot distinguish any kind of velocity for everybody and everything was at rest for him, but another massless observer placed in another light beam would be exactly at the velocity of the light with respect to him. Very crazzy behaviour which shows that our hipothesis of assuming a physical observer on an electromagnetic wave is wrong.
@ Daniel Baldomir
my dear Daniel Baldomir thank you....you are right.....if for suppose an observer travels with a speed of light do he able to calculate magnetic force with the help of length contraction?
Dear Hussainsha,
Your question is only in realm of the speculation or imagination because, I repeat, there are no real observer moving at the velocity of the light. That is impossible for relativity. But your question now is:
if for suppose an observer travels with a speed of light do he able to calculate magnetic force with the help of length contraction?
We can imagine the light as an observer, and then if it applies the length contraction it is going to obtain always zero, for every object that it can "measure". This is quite absurde because tell us that for light the radius of the Earth is the same as Bohr radius of an atom. Thus the conclusion is that light is out of the concept of length or time, actually lives only in the surface of the Minkowski's cone and it is a singularity of the Lorentz group SO(3,1).
On the other hand you ask how could it (imagining light making calculations) calculate magnetic force with the length contraction?
As you have seeing length contraction is always zero, thus this is not the way. But if we follow to assume that the light by itself could be an observer (just pure imagination). We could say the following statements:
1- Photons do not detect magnetic and electric fields because there is not an interaction. Another thing is electromagnetic field and photons.
2- The electromagnetic invariants associated to the fields for light are both zero. This tell us that we cannot exchange with light any dynamical variable as can be a force.
"observer travelling with a speed of light" is not possible in relativity theory.
s h s> My dear Kåre Olaussen so what happens at that speed?
Absolutely nothing:
https://www.youtube.com/watch?v=u8lx19V7SNg&feature=youtu.be
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