And all these years I thought it was because Steinmetz was Left-Handed !!
73, Dick, W1KSZ
On Thu, Sep 6, 2012 at 11:28 AM, Jim Garland <4cx250b@muohio.edu> wrote:
> I'd like to try and clear up a few misconceptions about charges and
> currents. As most of you know, physicist J.C. Maxwell in 1861 published the
> four equations bearing his name that described the properties of
> electricity. He made no mistakes in his equations or any wrong assumptions
> about the signs of charges. In fact, his equations never mentioned electrons
> or protons, neither of which had yet been discovered. However, even if they
> had been discovered, their discovery would not have changed his equations.
>
> The key idea in Maxwell's equations is the concept of electric
> and magnetic fields. This was a huge breakthrough in human understanding.
> Today, we know there are other kinds of fields - the gravitational field,
> two kinds of nuclear fields, and other more arcane ones. Maxwell observed
> that there is an electric field associated with every electric charge. An
> electric field is an example of a vector field, which means that at all
> points in space it has both a magnitude and a direction. For a point
> positive charge, the electric field radiates outwards to infinity. For a
> negative charge, like an electron, it points inward from infinity towards
> the charge.
>
> Now here is a key point, often not appreciated. While we think
> of point charges like electrons as tiny little particles, in fact they are
> huge. So huge in fact that each electron literally extends throughout the
> observable universe (aside from a few subtleties). The reason is that the
> electron's electric field is an integral part of the electron. If you wiggle
> an electron, the entire electric field cloud around it also wiggles, with
> the ripple spreading outward through the cloud at the speed of light.
>
> These fields are not just abstract, mathematical concepts. If
> you hold a charged object in "empty" space, it will be pushed on by whatever
> the value of the electric field is at that point in space. If the electric
> field is too strong, and you get too close, it will kill you. Fields
> permeate all of space. In space, matter is pretty scarce, but fields are
> everywhere.
>
> Now consider a ball of matter that has a bunch of positive
> charges on it and contemplate what happens if we make the ball less
> positive. We can do this by stripping away some of those positive charges,
> thus creating a "wind" of positive charges that flows away from the ball.
> This wind of positive charges creates an outward flow of electric current,
> but it is not the same thing as an electric current. The electric current is
> a more abstract concept that takes into account both the direction the wind
> is blowing and the sign of the charge carred in the wind. Like an electric
> field, the electric current is also a vector field that has both a magnitude
> and a direction at all points in space. In this example, the direction of
> the electric current vector points away from the ball.
>
> Of course we can also make the ball less positive by adding
> negative charges to it. Adding negative charges creates a wind of negative
> charge that flows in toward the ball. However the resulting electric current
> is still outward, because the minus sign on the negative charge cancels the
> minus sign on the direction of the inward pointing wind. In other words, the
> value of the current vector field is exactly the same, whether we have an
> inflow of negative charges or an outflow of positive charges. And it's a
> damn good thing it's the same, because if it wasn't all of ham radio, in
> fact all of electronics could not exist.
>
> I know some of you are puzzled by the seeming paradox of all
> this. To some, it seems odd and non-intuitive that heating a filament in a
> vacuum tube to boil off electrons would cause current to flow from a distant
> anode toward the filament. But there is no paradox. The paradox is really
> just a failure to understand that electric current is a generalized concept,
> in which a positive charge moving to the right is exactly equivalent to a
> negative charge moving to the left. Electronics is filled with these kind of
> seemingly non-intuitive things. For example, we often hang a filter
> capacitor on a bridge rectifier to shunt the AC ripple current to ground.
> Yet there is no charge that passes through the filter capacitor. The only
> thing between the plates of the capacitor is an electric field.
>
> All of this was figured out about a hundred and fifty years ago
> by some very bright people who devoted their lives to understanding it. I
> think we owe them the benefit of the doubt. If we don't understand what they
> did, then the problem lies with us, not them. If that's the case, then it
> may be time for us to start hitting the books and try to be a bit more
> flexible in our thinking.
>
>
>
> 73,
>
> Jim Garland W8ZR
>
>
>
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