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Tue 25 Aug, 2015 11:14 pm
Context:
Anyone who sits through a freshman electricity and magnetism course learns that charged objects carry electric fields, and that moving charges also create magnetic fields. Hence, moving charged particles carry electromagnetic fields. Late 19th-century natural philosophers believed that electromagnetism was more fundamental than Isaac Newton’s laws of motion and that the electromagnetic field itself should provide the origin of mass. In 1881 J. J. Thomson, later a discoverer of the electron, made the first attempt to demonstrate how this might come about by explicitly calculating the magnetic field generated by a moving charged sphere and showing that the field in turn
induced a mass into the sphere itself.
More:
http://www.scientificamerican.com/article/was-einstein-the-first-to-invent-e-mc2/
@oristarA,
It means the magnetic field caused the sphere to have mass.
@chai2,
chai2 wrote:
It means the magnetic field caused the sphere to have mass.
So a charged sphere at rest has no mass? It doesn't hold water.
@oristarA,
I think that's because Thomson's hypothesis was wrong.
@FBM,
Cool.
Any direct evidence that shows he said the zero mass of a charged sphere?
@oristarA,
I don't know of anything. Maybe later I'll get a chance to look it up.
Quote:...induced a mass into the sphere itself.
I read this indefinite article to mean that
some additional mass is induced, not the total mass of the sphere.
@FBM,
FBM wrote:
Quote:...induced a mass into the sphere itself.
I read this indefinite article to mean that
some additional mass is induced, not the total mass of the sphere.
That is exactly what I said in the title of the thread: Does "induced a mass into the sphere itself" mean "induced a mass (
to be added) into the sphere..."?
@oristarA,
Ah. OK. So what did you mean by
Quote:zero mass of a charged sphere
That's not implied by the context, as far as I can see.
The article goes on to state:
"The effect is entirely analogous to what happens when you drop a beach ball to the ground. The force of gravity pulls the ball downward; buoyancy and drag forces from the air impede the ball’s fall. But this is not the whole story. Drag or no drag, in order to fall the ball must push the air ahead of it out of the way and this air has mass. The “effective” mass of the falling beach ball is consequently larger than the mass of the ball at rest. Thomson understood that the field of the sphere should act like the air before the beach ball; in his case the effective mass of the sphere was the entire mass induced by the magnetic field.
Thomson’s slightly complicated result depended on the object’s charge, radius and magnetic permeability, but in 1889 English physicist Oliver Heaviside simplified his work to show that the effective mass should be m = (4⁄3) E / c2, where E is the energy of the sphere’s electric field. German physicists Wilhelm Wien, famous for his investigations into blackbody radiation, and Max Abraham got the same result, which became known as the “electromagnetic mass” of the classical electron (which was nothing more than a tiny, charged sphere). Although electromagnetic mass required that the object be charged and moving, and so clearly does not apply to all matter, it was nonetheless the first serious attempt to connect mass with energy." (emphasis mine)
@oristarA,
Quote:So a charged sphere at rest has no mass? It doesn't hold water.
He doesn't say, and he doesn't mean, that the sphere started off with no mass. He says only that a mass (an increase in mass) is brought about.
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