A Coil, the Current and the Voltage

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Chris posted this 30 July 2017

At any one point in time, given the Magnetic Field B, we have two states that are possible in a Coil of Insulated Wire. These States are different when a Coil is being Driven, or Induced. What do I mean?

The Two States:

  1. Driving a Current into a Coil, by applying a Voltage across the Coil.
  2. An E.M.F (Electromotive Force) that is induced in a Coil.

State One, where we apply a Voltage across a Coil, we are driving the Coil and as a result, the Current will be in one direction, and the Voltage polarity in the other. If the Voltage across a Diode is Negative, no Current can flow. The Diode is said to be Off or Reverse Biased.

Figure One: The Capacitor does not charge, there is no path for the Current.


When the Mosfet is on, we have applied 10 Volts across the Coil:

Figure Two: Voltage applied across the Coil.



State Two, where an E.M.F is induced in the Coil, invoking Electromagnetic Induction, a discovery of Michael Faraday, some 186 years ago. Here we have Voltage and Current in the same direction.The Mosfet (Q1) is switched off, breaking the Voltage Applied across the Coil, the Coil’s Voltage Polarity reverses, and the Diode Conducts. With a positive Voltage across the Diode, it becomes Forward Biased and is now On.

Figure Three: We have Charge across the Capacitor.


When the Mosfet is switched off, the Magnetic Field B collapses and the Coil’s Voltage Polarity reverses, but the Current flow remains in the same direction.

Figure Four: The Induced E.M.F = -N dPhi/dt


Where the 100 Volts is the E.M.F Induced by Faradays Law of Induction. This is the Magnetic Field Collapsing, changing over time in proximity of the turns N.

And so, we can see now, how a Coil of Insulated Wire, has Two States!

It’s worth noting, Current flows have been mixed up over the years by Science. It’s not hard to see why; it is confusing to say the least. Let’s look at another example:


Figure Five: The Symbol for a Diode.


Figure Six: Diode Conducts and Capacitor Charges.


Figure Seven: Diode does not conduct and the Capacitor does not Charge.


Figure Eight: What is Current?


So what is the Current, what is it a flow of? The very word “Current” is defined as a movement of something! Yes, isn’t it confusing!


Figure Nine: Flow of Charges.


We have learned, in the Mr Preva Experiment, that we can Increase the Total Current in a Localised Circuit and thanks to the wise words of Floyd Sweet we know what this means:

In the specific case of positive charges moving to the right and negative charges to the left, the effect of both actions is positive charge moving to the right.

Current to the right is: I = da+ / dt + da- / dt.

Negative electrons flowing to the left contribute to the current flowing to the right.


Most likely the Positive Charges moving to the Right are Ions. But to be honest, who really knows.

So the Coil Changes, depending on what’s going on. What the Coil is being used for. It is an Active Element, acting like a Battery, when an E.M.F is Induced. Or if a Voltage is applied across it, it is a Passive Component, exhibiting the above mentioned change in Voltage Polarity after the applied Voltage is switched off.

I hope this helps some! Please point out any mistakes also, we want to get this as accurate as possible for others following.


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Chris posted this 30 July 2017

Hi Vasile, Sorry, I used what I thought we would all be very familiar with. Was only as an example.

The Important thing I was trying to cover, was that Coils Polarity and Current Flow.

I have seen what I believe to be much confusion surrounding Coils, Diodes, Voltage and Current, polarity's and directions, even by some advanced people over the years.

One example: Fet Diode Test

A test, I have seen this many times here on this forum!!!

What LED's will Light:

   D1: ?
   D2: ?
   D3: ?


Use the Right Hand Grip Rule to find the Polarity of the Magnetic Field, this is easy, but if one is not sure on the Current Direction, then this is not so easy!


Hope this clear up any possible confusion...



Chris posted this 20 October 2020

My Friends,

An article I feel is important for us. FACT: Electron moving, is Current!

Tiny device pumps out one electron at a time

02 Dec 2016  

One at a time: the single-electron pump. (Courtesy: PTB)

Physicists should finally be able to rid themselves of the cumbersome and inaccurate definition of the ampere. That is the claim of metrologists in Germany, who have measured electrical current by counting single electrons travelling along a microscopic wire. The researchers say that their technique will allow scientists in a number of different disciplines to make better measurements of tiny currents.

The move to revamp the ampere is part of a more general overhaul of the SI system of units. It is envisaged that all seven base units – the ampere, second, metre, kilogram, kelvin, mole and candela – will be anchored to unvarying constants of nature. In particular, scientists are eager to redefine the kilogram, which is currently based on the mass of a specific lump of platinum-iridium sitting in a Paris safe and slowly shedding atoms.

It is partly to sever its link with the kilogram that metrologists are keen to redefine the unit of electrical current. At the moment, one ampere is defined as the current flowing in two narrow, infinitely long parallel conductors placed one metre apart in a vacuum that generate between them a force of 2 ×10–7 N for every metre of length. This formulation is a problem because it means that the ampere is defined in terms of the kilogram (as well as the metre and the second) because force is equal to mass times acceleration. Also, nothing can be infinitely long, so this requirement must be approximated somehow.

Transistor-like device

This latest work was carried out by Frank Hohls and colleagues at the German National Metrology Institute (PTB) in Braunschweig and aims to define the ampere in terms of a certain (large) number of single electrons passing through a conducting channel in unit time. Central to the proposal is the construction of a “single-electron pump”, a transistor-like device that transmits just one electron when activated by a gate voltage. With the voltage oscillating perhaps several billion times a second, the device would generate a current that is large enough to calibrate an ammeter – thus revealing how accurate the instrument is.

The team made single-electron pumps from quantum dots – sub-micron sized conducting areas etched on to semiconductor substrates. Operating the pumps at millikelvin temperatures, they apply a roughly 0.5 GHz gate voltage and a second, fixed voltage across each dot to set up a time-varying potential well that briefly captures and then ejects single electrons. To establish the accuracy of their devices, the researchers use a specially developed amplifier that converts the current flowing through it into a voltage, which is measured by a voltmeter calibrated using two other quantum phenomena – the quantum Hall effect and the Josephson effect.

The researchers were able to measure the current transmitted by the pumps with an accuracy of 0.16 parts per million. This is fractionally better than they achieved with an earlier version of their device last year, which matched the accuracy of measurements that can be carried out using the existing force-based definition of the ampere – 0.2 parts per million. The new measurements were also done more quickly – requiring just 21 hours, rather than the several days employed a year ago. “The measurement set-up used in this experiment represents the state-of-the-art in small-current metrology,” says group member Hansjörg Scherer.

Aerosol counting

According to Scherer, who led the PTB effort to design the new amplifier, more accurate measurements made possible by the pumps could prove useful in a number of areas. Among them, he says, are the determination of radioactivity levels in ionization chambers and counting aerosol particles in the air.

Ian Mills, a metrology expert at the University of Reading in the UK, praises the “valuable and excellent work” being done on electron counting at the PTB. But he believes that a better definition of the ampere can be obtained simply by using the most accurate value for the electron charge available today – which is based on other measurements including that of the fine structure constant. That value of the ampere has an accuracy of about 20 parts in a billion and is, he says, most likely to be used in the new definition of the ampere that should be approved by the General Conference on Weights and Measures – the body that will authorize changes to the SI system. “I think the electron-counting experiments are fascinating,” he says, “but they are not yet sufficiently precise to compete.”

François Piquemal of the National Metrology and Testing Laboratory (LNE) in Paris, takes a slightly different view, arguing that electron counting offers a way of realizing the ampere in practice, rather than defining it. He maintains that single-electron pumps are best suited to measuring currents up to about a nanoamp, while an alternative approach – involving the combination of quantum Hall and Josephson standards through Ohm’s law – is best for larger currents. “In my opinion, these two methods are complementary for the future mise en pratique of the ampere,” he says.

Ref: Tiny device pumps out one electron at a time - physicsworld.com


Take special note of the Right Angle of the device, this is The Lorentz Force.

This article uses a slew of very important words: Acceleration, Electrons, Travelling, Time-Varying Potential and more.

Best wishes, stay safe and well My Friends,


Forushani posted this 5 days ago

what is the appropriate Diode to use on the coils?

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  • Chris
Chris posted this 5 days ago

Hi Forushani,

Don't forget: Keep it simple.

Any diode that's within the ratings. Ratings of Voltage and Current within what you want to use it for. Later, when you have more specific uses, this can get a little more complicated. But, for now, Simplicity is Key.

Best Wishes,



P.S: See the Diode's Datasheet for the Ratings.


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Ere many generations pass, our machinery will be driven by a power obtainable at any point of the universe. This idea is not novel. Men have been led to it long ago go by instinct or reason. It has been expressed in many ways, and in many places, in the history of old and new. We find it in the delightful myth of Antheus, who drives power from the earth; we find it among the subtle speculations of one of your splendid mathematicians, and in many hints and statements of thinkers of the present time. Throughout space there is energy. Is this energy static or kinetic? If static, our hopes are in vain; if kinetic - and this we know it is for certain - then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature.

Experiments With Alternate Currents Of High Potential And High Frequency (February 1892).