On May 26, 7:11 am, Timo Nieminen <
t...@physics.uq.edu.au> wrote:
> On Saturday, 25 May 2013 11:10:15 UTC+10, Larry Harson wrote:
> > Here's what I consider to be the fundamental difference between an
> > electric and a magnetic field:
> [...]
> > Do you guys agree, or are there simpler definitions?
>
> Following Stratton, we have two sets of definitions:
>
> 1. In terms of sources, D depends on charge (density), H depends on current (density).
I'd say D also depends on current since it depends on the velocity of
a moving charge.
> 2. In terms of effects, E affects charge, B affects currents (or moving charge).
I'd say E affects moving charge and therefore currents as well.
> We can add some stuff about material media (or particles) with electric or magnetic dipole moments.
>
> I think both of these are simpler definitions.
By current, maybe Stratton means moving charge whose electric field is
cancelled by an opposing electric field from stationary charges.
> But to look at your definition, if your "accelerated" includes the case of a=0, then it's pretty general. What is lacking is a concrete idea of what "electromagnetic force at that point" means.
Typo, you meant v=0?
Since an electron can be accelerated by forces other than
electromagnetic, then it's essential to also include sources, which
I'll now include:
1. Electromagnetic forces cause charge to accelerate, and consist of
two types: Electric forces are created by and act upon both a moving
and stationary charge. Magnetic forces are created by and act upon
only moving charge.
From this, it still isn't obvious to me how the magnetic force
component can be unambiguously separated from the electric component.
Which means still appealing to the lorentz force equation for
additional information:
d/dt(gamma m v) = q(E + vxB)
The acceleration of the charge q depends upon its velocity for both E
and B. But the acceleration contributed by E is independent of the
direction of v of the charge q, unlike that for B, and that seems to
be a crucial difference between E and B.
In the original post, I used the direction of acceleration to
distinguish between E and B, which isn't general enough upon
reflection, which now gives:
2. The electric force causes a charge to accelerate independently of
the direction of its velocity, a magnetic force doesn't.
Regards, Larry.