About fields

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Are fields like magnetic fields made of particles/waves that travel from the source outwards? For example, if you put an obstacle(that would not let photons pass) between the source and a charged object, would the charge be affected? Or do fields interact with objects independantly from what's between the source and the object?

Thanks,

Alex
 

HallsofIvy

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Strictly speaking, a "field" is simply a value of some quantity at each point in space. One can have waves IN a field (i.e. the values are changing in a wave-like manner) but it would be incorrect to talk about a field as "made of" of waves or particles.

Light, for example, is a wave in an electro-magnetic field (in order to have waves, the field must have both electric and magnetic components- a magnetic field alone will not produce waves). At the quantum level (and in particular at the level of individual light waves), the distinction between particles and waves blurs and you can think of it as being either one.
 
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Originally posted by HallsofIvy Light, for example, is a wave in an electro-magnetic field (in order to have waves, the field must have both electric and magnetic components- a magnetic field alone will not produce waves)
This is not quite correct. The basic field is the electric field. The electric field derives from charged particles, most frequently electrons.

Any motion of the charged particles causes kinks in its electric field. these kinks are electromagnetic waves. All electromagnetic waves are kinks in an electric field.

When the motion of charged particles is constant and along a defined path, as when current flows in a wire, the kinks in the electric field are also constant and we can detect a coherent magnetic field.

The electric field is radiant, pointing out in all directions from the charged particle. The waves in the electric field that form the magnetic field are transverse.

The above describes the action whereby all magnetic fields are generated: from electric fields. Magnetic fields are waves in electric fields. With this in mind, you will see why it is not quite correct to say: "in order to have waves, a field must have both electric and magnetic components." We only need start with an electric field. We "wave" it (move it somehow) and the magnetic component follows.

Therefore "...a magnetic field alone will not produce waves", is true, but true because the magnetic field is, itself already waves. There really is no such thing as a "magnetic field alone" with no electric component. If there is no electric component, there is no magnetic component, since the latter derives from the former.
 
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Thx for replies guys. So could a field (or at least its effects) be blocked by an obstacle, or does it affect all the matter (well, charged matter for electro-magnetic fields) in its area of effect (which is infinite for electro-magnetic and gravitationnal fields, right?), regardless of obstacles and the like?

Alex
 

drag

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It can't be blocked, but it can be canceled by other fields
or even by itself.
 

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