I Question about electromagnetism and frames of reference

abdossamad2003
Messages
68
Reaction score
4
in this text:
1.jpg


my question is in highlighted line:
"The two rods have the same length (in S) and contain the
same number of charges." why?

Considering that the negative rod has movement, it should have a shorter length than the positive rod according to a relativity!
 
Physics news on Phys.org
abdossamad2003 said:
in this text:
View attachment 340896

my question is in highlighted line:
"The two rods have the same length (in S) and contain the
same number of charges." why?

Considering that the negative rod has movement, it should have a shorter length than the positive rod according to a relativity!
There was a long thread about this recently. If you set up a steady current in an infinite length of wire, then it's not clear whether the moving charges get closer together or not. It all depends on how you accelerate them.

If, however you consider a physically realistic large rectangular loop of wire, then the moving charges must have the same charge density, as no charges gave been added or taken away from the wire. This is in the rest frame of the wire.

This means that in the rest frame of the moving charges in a section of the wire, the charges must have got further apart. And the stationary charges will be closer together in this frame.

Note that there is no single rest frame of the moving charges throughout the whole loop.
 
abdossamad2003 said:
my question is in highlighted line:
"The two rods have the same length (in S) and contain the
same number of charges." why?

Considering that the negative rod has movement, it should have a shorter length than the positive rod according to a relativity!
The authors of this book assume, that the rest length of the rod, which is moving in frame ##S##, is greater than the rest length of the other rod at rest in frame ##S##.

"It is a well-known fact that a current-carrying wire is neutral ... in the lab frame", and therefore a positive surface charge density must compensate the negative volume charge density, according to
http://web.mit.edu/wangfire/misc/AJP000360.pdf
 
Last edited:
In this video I can see a person walking around lines of curvature on a sphere with an arrow strapped to his waist. His task is to keep the arrow pointed in the same direction How does he do this ? Does he use a reference point like the stars? (that only move very slowly) If that is how he keeps the arrow pointing in the same direction, is that equivalent to saying that he orients the arrow wrt the 3d space that the sphere is embedded in? So ,although one refers to intrinsic curvature...
I started reading a National Geographic article related to the Big Bang. It starts these statements: Gazing up at the stars at night, it’s easy to imagine that space goes on forever. But cosmologists know that the universe actually has limits. First, their best models indicate that space and time had a beginning, a subatomic point called a singularity. This point of intense heat and density rapidly ballooned outward. My first reaction was that this is a layman's approximation to...
So, to calculate a proper time of a worldline in SR using an inertial frame is quite easy. But I struggled a bit using a "rotating frame metric" and now I'm not sure whether I'll do it right. Couls someone point me in the right direction? "What have you tried?" Well, trying to help truly absolute layppl with some variation of a "Circular Twin Paradox" not using an inertial frame of reference for whatevere reason. I thought it would be a bit of a challenge so I made a derivation or...

Similar threads

Replies
87
Views
5K
Replies
61
Views
5K
Replies
15
Views
2K
Replies
23
Views
1K
Replies
24
Views
2K
Back
Top