Electricity is magnetism

By: Adrian (a.delete@this.acm.org), December 15, 2021 5:06 am
Room: Moderated Discussions
Brett (ggtgp.delete@this.yahoo.com) on December 14, 2021 3:01 pm wrote:
> Electricity is magnetism:
> https://youtu.be/bHIhgxav9LY
> The electrons barely move and it is the magnetism doing all the work.
> This should be mind blowing for at least half the people here.
> Has implications for multi-fin transistors, splitting the wire and wiring up the fins like interleaved fingers
> should result in stronger more efficient fields for a better transistor, at the cost of more area.
> Line of sight matters and not wire length, which adds a little chaos to delay calculations.
> So looping around to get into a ALU does not matter, besides wasting area.

No, electricity is not magnetism.

For any words A and B, if you redefine both words to mean C, then you can claim that A is B.

Especially for words belonging to scientific or technical fields, many people do not know their precise meaning and they frequently use them with inappropriate meanings.

That video, like most that contain misinformation, contains a mixture of true facts with false facts.

The word electricity has several distinct meanings.

After the first 3 quarters of the 19th century, during which it was discovered (as a consequence of the invention of the Volta battery in 1800) that the formerly distinct phenomena of magnetism, light and radiant heat have the same cause as those considered formerly as belonging to electricity, electricity can be used in a general sense, so one can say e.g. just "the theory of electricity" for what would have been previously called "the theory of electricity, magnetism, light and radiant heat".

So when electricity is meant in its general sense, one can say that magnetism is electricity, but not that electricity is magnetism.

On the other hand, when electricity and magnetism are meant in their original sense, they refer to separate phenomena caused by the electric forces and magnetic forces.

The separation of the forces between electric charges is not always useful, but when it is done, the force has 3 components (not 2 as it is frequently wrongly said in many elementary manuals).

In the non-relativistic approximation, the 3 components are the electric force, which depends on the distance between electric charges, whose expression was determined by Coulomb in 1785, the magnetic force, which depends on the relative velocity between charges, whose expression was determined by Ampere in 1823 and the third component is the inductive force, which depends on the relative acceleration between the electric charges, which was discovered experimentally by Faraday in 1831 and whose expression was determined by Weber in 1846.

The third component, the inductive force, which is clearly distinguished by the electric forces and the magnetic forces by being dependent on the relative acceleration, is what causes not only the induction of currents in conductors, but also the radiation of electromagnetic waves.

So when you use correctly the words, there is no doubt which is electricity and which is magnetism.

There are special cases when you have only electric forces, i.e. when there are only stationary electric charges and there are cases when there are only magnetic forces, i.e. when you have a system of stationary constant electric currents.

In most practical applications you have either variable electric currents or moving parts, so all the 3 components of the electromagnetic force are present and it usually there is not much advantage in trying to consider separately the electric, magnetic and inductive components.

Most manuals about electromagnetism present simplified variants of the so-called Maxwell's equations, which have very little connections with the Maxwell equations, as used by Clerk Maxwell himself, and which are valid only in certain very restricted circumstances, which are seldom mentioned in the manuals.

Computing the Poynting vector, like in the video, is better avoided, because computing it as shown in manuals only seldom gives values that correspond to any real energy flow.

Also, computing the electric and magnetic field vectors (usually noted E and B), like in the video, is seldom useful. This are just intermediate quantities, used to compute the relationship between the clearly meaningful quantities that are the electric charges and currents and the forces that act upon them.

It is better to use as intermediate quantities the electric and magnetic potentials, both because it is easier computationally and because it is harder to make mistakes with them. With the manuals that show only simplified formulas for computing E and B, wild mistakes and wrong interpretations, like in the video, are frequent.

Going back to the video, its claims about the energy flow behaving unexpectedly are incorrect.

The electromagnetic field is what causes the forces, it propagates with the speed of light and it generates forces that start moving the electrons all over the circuit, lighting the bulb after the switch is closed.

There is nothing new or unexpected about this.

There is no need to use the vectors E and B to visualize this, just the scalar electric potential is enough, the vectors E and B do not provide any extra information.

With the switch open, the electric potential is null everywhere in the circuit of the bulb.

When the switch is closed, there is a transitory phase during which the so-called electromotive force of the power supply pumps electrons between its terminals and the voltage, i.e. electric potential difference between the extreme points of the circuit rises quickly from 0 to the steady-state value.

Because the dimensions of most parts of the circuit are small, the voltage in all the intermediate points close enough spatially to the power supply will also rise proportionally to the maximum phase.

During the transitory phase, all the electrons in the parts of the circuit close enough to the power supply are accelerated almost simultaneously from null speed to the small steady-state speed, acquiring a modest kinetic energy that was transmitted from the power supply through the electromagnetic field, with the speed of light.

In the steady-state, the electrons move at constant velocity through the bulb and wires, generating heat by friction. The loss of energy by heat is compensated by the energy gained while the electrons move at that steady-state speed to points of different electric potential (like a body sliding downhill, which provides heat by friction).

There is a steady-state flow of energy from the power supply, which maintains the electric potential constant everywhere.

While things like the energy of the electrons, e.g. the potential energy gained by electrons when passing through the power supply or lost when passing through a resistor, or the heat and work exchanged by subsystems, can be precisely defined and measured, thinking about energy stored in the electromagnetic field or flowing with it are very tricky.

The literature about the energy supposedly stored or flowing through the electromagnetic field is full of mistakes, of contradictory definitions, of wrong formulas and wrong computations.

For practical applications that does not matter, because only the end results matter, i.e. which are the energies provided by power supplies and consumed in various devices and for these there is no need to compute any energies that might be stored or flowing through the field.

You just need an appropriate computational method that would compute the electric and magnetic potentials and the distributions of electric charges and currents, then any quantities of interest can be computed without playing with irrelevant unmeasurable quantities.

So the video just plays with words and it presents normal circuit behavior as unexpected.

The only right part of it is stressing that if you have a circuit with parts close to the power supply and parts very distant to it, the electromagnetic field will propagate instantaneously to all the near parts, so conduction in them can start immediately, while the distant parts, regardless where they are placed in the circuit, will behave as long lines so at their insertion point in the circuit they might have an inductive, capacitive or resonant behavior. Depending on the details of the circuit, the bulb may light immediately as in the video, or not, in other cases.

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TopicPosted ByDate
Electricity is magnetismBrett2021/12/14 04:01 PM
  *facepalm* (NT)Ray2021/12/14 05:16 PM
    in fairness what started out trollish turned into a really informative thread (NT)anonymous22021/12/15 06:55 PM
  Electricity is magnetismAnon2021/12/14 06:16 PM
    Electricity is magnetismLightning2021/12/14 06:47 PM
      Electricity is magnetismDavid Hess2021/12/14 10:47 PM
    Electricity is magnetismBrett2021/12/15 12:12 PM
      Electricity is magnetismSimon Farnsworth2021/12/15 02:30 PM
      Electricity is magnetismAnon2021/12/15 03:03 PM
      Electricity is magnetism---2021/12/16 12:19 PM
        Electricity is magnetismAdrian2021/12/16 03:51 PM
  Electricity is magnetismAdrian2021/12/15 05:06 AM
    Sorry for a few typos, I was in a hurry, but the typos do not affect the meaningAdrian2021/12/15 05:40 AM
    Electricity is magnetism2021/12/16 06:22 PM
      Electricity is magnetismEtienne Lorrain2021/12/17 02:44 AM
        Electricity is magnetismBrett2021/12/17 01:44 PM
      Electricity is magnetismAdrian2021/12/17 05:24 AM
        Electricity is magnetism2021/12/17 02:49 PM
          Electricity is magnetismAdrian2021/12/18 03:54 AM
            Electricity is magnetismAdrian2021/12/18 04:17 AM
              Electricity is magnetismanon12021/12/19 03:51 AM
                Electricity is magnetismAdrian2021/12/19 05:13 AM
                Electricity is magnetismDavid Hess2021/12/19 06:54 PM
  Electricity is magnetismzArchJon2021/12/15 11:53 AM
  This video is just really totally wrong..., sorry.Hans de Vries2021/12/15 06:26 PM
    This video is just really totally wrong..., sorry.anon2021/12/16 05:03 AM
  Electricity is magnetismBrett2021/12/19 06:02 PM
    Electricity is magnetismDavid Hess2021/12/19 07:11 PM
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