Register to reply

EM waves- self propagating in a vacuum?

by kasap
Tags: propagating, vacuum, waves
Share this thread:
kasap
#1
Oct23-13, 07:59 AM
P: 6
First of all, I understand that an EM wave is created by a charged particle that is moving.

What I don't understand is how it propagates itself when travelling through a vacuum as there is no medium for it to interact with. Can this be explained by anything other than photon theory? I really can't wrap my head around the idea of self propagation.

Sorry in advance if this question is a load of rubbish, thanks.
Phys.Org News Partner Physics news on Phys.org
Step lightly: All-optical transistor triggered by single photon promises advances in quantum applications
The unifying framework of symmetry reveals properties of a broad range of physical systems
What time is it in the universe?
DaleSpam
#2
Oct23-13, 08:29 AM
Mentor
P: 17,318
Quote Quote by kasap View Post
Can this be explained by anything other than photon theory?
Certainly. It was first explained by Maxwell's equations:
http://en.wikipedia.org/wiki/Maxwell...speed_of_light
rude man
#3
Oct24-13, 02:28 AM
HW Helper
Thanks
PF Gold
rude man's Avatar
P: 4,851
Quote Quote by kasap View Post
First of all, I understand that an EM wave is created by a charged particle that is moving.

What I don't understand is how it propagates itself when travelling through a vacuum as there is no medium for it to interact with. Can this be explained by anything other than photon theory? I really can't wrap my head around the idea of self propagation.
Well, you must.

Close to the oscillating charge the field is dependent on the oscillating charge, but as the field expands it continually renews itself by alternately generating E and H fields. The cause of the field, the oscillating charge, is essentially "forgotten"!

kasap
#4
Oct24-13, 06:52 AM
P: 6
EM waves- self propagating in a vacuum?

Thanks to both of you for your replies,
Quote Quote by rude man View Post
Well, you must.

Close to the oscillating charge the field is dependent on the oscillating charge, but as the field expands it continually renews itself by alternately generating E and H fields. The cause of the field, the oscillating charge, is essentially "forgotten"!
Thank you this makes more sense now, I looked up Maxwell's equations and saw that a changing magnetic field gives rise to an electric field and vice versa. But what causes them to change, is it not that the source (the oscillating charge) is constantly changing position? Sorry in advance if this is a stupid question.
mikeph
#5
Oct24-13, 08:32 AM
P: 1,212
What causes them to change? That is just how they are. Is it any more mysterious than the fact that charges and current create the fields in the first place?

Physics isn't really in the habit of answering "why" questions.
DaleSpam
#6
Oct24-13, 09:55 AM
Mentor
P: 17,318
Quote Quote by kasap View Post
But what causes them to change, is it not that the source (the oscillating charge) is constantly changing position?
The charge need not continue to change position. If it briefly changes position and then remains at rest then there will be a brief wave which will propagate at the speed of light forever (in principle).
Nugatory
#7
Oct24-13, 10:37 AM
Sci Advisor
Thanks
P: 3,747
Quote Quote by kasap View Post
But what causes them to change, is it not that the source (the oscillating charge) is constantly changing position? Sorry in advance if this is a stupid question.
The initial disturbance is created by the moving charge, but once created it will continue to propagate. Intuitively, it's not all that different from what happens when you toss a rock into a pool of still water - the ripples keep spreading long after the rock has quietly sunk to the bottom.
mesa
#8
Oct24-13, 11:06 AM
P: 553
Quote Quote by mikeph View Post
What causes them to change? That is just how they are. Is it any more mysterious than the fact that charges and current create the fields in the first place?

Physics isn't really in the habit of answering "why" questions.
DaleSpam andf Nugatory have done well in answering 'why'. It's a really cool topic although I would look at Faradays basic ideas on Bf and how they are created by moving charges (from your 'static' frame of reference) as opposed to Maxwell's equations for more simplicity in understanding how these EM waves propagate through space.


Register to reply

Related Discussions
Propagating waves in string Introductory Physics Homework 2
Polarizations of plane waves propagating in anisotropic media Classical Physics 12
Waves in periodic structures - Coupling of evanescent waves to propagating waves Atomic, Solid State, Comp. Physics 5
Waves in periodic structures - Coupling of evanescent waves to propagating waves Classical Physics 1
Are there propagating charged waves admitted in Maxwell’s equations? Differential Geometry 0