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No, Faraday’s law of induction is not true.
One of the fundamental laws of electromagnetism is the “Faraday's law of induction”. This law states that the induced voltage in a wire loop is equal to the speed of change of the magnetic flux enclosed with the loop, or V=dΦ/dt. In the textbooks is often given an example of a loop in the shape of a rectangle which rotates in a magnetic field. (please click on the images for a bigger view)
post-96058-0-76960900-1580069399_thumb.png
What is meant by “the speed of change of the magnetic flux enclosed with the loop”?
To explain this, we will make a comparison. If we hold a ring in front of our eyes as if we want to see through it, then it has a shape of a circle. If we turn it 90°, we only see a line. In every other intermediate position of the ring, we see an ellipse. In the first position, the ring has the maximum area in front of our eyes; in the second, the minimum, i.e., zero. If the ring starts to rotate about its axis starting from the second position (0) and has turned 180°, then the area we see in the course of this rotation can be represented with a sine curve of half a period.
Similarly, when the wire loop is in the vertical position (image above), then the magnetic flux is zero, and when the wire loop is in the horizontal position, then the flux is maximal. This flux changes according to a sine function, too. So, when the flux is maximal, then the speed of its change is minimal, more precisely, zero, because the slope of the sine curve in this point is zero. But when the flux is minimal, then the speed of its change is maximal, because the slope of the curve in this point is maximal.
So, from the Faraday's law of induction it follows that when the wire loop is in vertical position, then the induced current in the loop is maximal; and when it is in horizontal position, then the current in the loop is zero.
I claim that just the opposite is true, because it is not relevant the speed of change of the magnetic flux through the loop, but the speed of the wire towards the magnet or away from it. In producing the current in the rectangular loop, only the two shorter sides of the loop play a role. When these sides are nearest the magnet, then their speed of moving towards or moving away from the magnet is zero, thus the current is also zero.
For better understanding, let’s take a look at this picture. The projection of the circling dot on the vertical axis behaves like a pendulum. When the projection dot is at the top or at the bottom of the vertical axis, its speed is zero. And when it is in the middle, its speed is maximal. The same concept applies also to the two mentioned sides of the wire loop.
post-96058-0-79593100-1580069664_thumb.png
I claim that the concept of the contemporary physics called “magnetic flux through a surface” is an absolute misconception, something that is not founded in the reality. What real is and what relevant is to this case are two things: first, the strength of the magnetic field, and second, the speed of the conductor towards the magnet or away from it, that is, the component of this speed which is in line with the magnetic lines of force, not the component perpendicular to them, as it follows from the Faraday’s law of induction.
As a consequence of this misconception follows another, and that is the misexplanation of the working principle of synchronous generators and motors. Let’s look at this picture from a textbook called “Elektronik 1” from the following authors: Helmut Röder, Heinz Ruckriegel, Willi Schleer, Dieter Schnell, Dietmar Schmid, Werner Zieß, Heinz Häberle. The picture refers to synchronous motor, but it can also refer to synchronous generator. On the picture we see a magnet, three coils and three sine curves: black, blue and red. The black sine curve corresponds to the current of the black coil. From the picture we see that in the first position of the rotating magnet the current in the black coil is zero; in the second position, the current in that coil is maximal.
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Just the opposite is actually true (this means: in the first position the current in the black coil is maximal; in the second, it is zero). And with this new explanation the torque from the coils upon the rotating magnet is the same at every moment of time, as it should be for its smooth rotation.
The other concept is contradictory, because the torque is not the same at every moment. Let’s take a look at the second position of the magnet when it is in line with the black coil (the current at this moment is at maximum)(the magnet rotates counter-clockwise). Until this moment the coil has attracted the white pole; then the pole goes to the left side of the coil; the coil still has the current in the same direction, which means that it still attracts the pole and thus acts against the direction of rotation. At the same moment (i.e., when the magnet is in line with the black coil) the blue and the red coil have equal currents in the same direction and both act on the opposite pole of the magnet. Thereby both exercise an attractive force. It follows that the red coil attracts the lower pole of the magnet in the direction of rotation and the blue coil attracts it against the direction of rotation. We see that on two places, both up and down, contradictory effects take place. When the upper pole of the magnet has passed the black coil a little bit, then of the three coils only the effect of the red one on the magnet will be in the direction of rotation, making the whole assembly impossible.
When the pole of the rotating magnet is moving towards the coil, then the coil attracts it. When the pole is exactly in line with the coil, then the current comes to zero, the magnetic field, too. Then a current flow begins in the contrary direction, the magnetic field of the coil is reversed and it begins to repel the pole of the magnet. This applies to a motor. The reverse applies to a generator.
 
Added: 03 August 2020

How does the induced current in a rotating loop look like?

 
Consider the following experiment:
post-96058-0-96257300-1596447573_thumb.jpg
 
A straight conductor is moving vertically exactly towards the middle of a magnet (figure A). No current is induced in this conductor.
In the second variant the conductor is shifted 1 millimeter to the right and is moving again vertically towards the magnet (figure B ). A current is induced in it which flows away from us.
In the third variant (figure C) the conductor is shifted 1 mm to the left and is moving vertically towards the magnet again. A current is induced in it which flows towards us.
 
Consider now this experiment:

post-96058-0-44655700-1596447750_thumb.jpg

A straight conductor is moving vertically exactly in the middle between two identical magnets as in the figure A above. No current is induced in this conductor.
In the figure B the conductor is shifted 1 millimeter to the right and is moving again vertically from the lower to the upper magnet. A current is induced in this conductor. But during its movement upwards, the induced current changes its direction. To the dashed line (which is exactly in the middle between the magnets) the induced current flows towards us. When the conductor is exactly in the middle, the current drops to zero. Then, above the dashed line, begins a current flow in the opposite direction.
In the figure C the conductor is shifted 1 millimeter to the left and is moving again vertically from the lower to the upper magnet. A current is induced in it, but here happens the reverse with respect to that of the figure B.
 
Please look now at the figure below.

post-96058-0-35042400-1596447907_thumb.jpg

A straight conductor is rotating uniformly counter-clockwise in a homogeneous magnetic field according to the figure (what is meant by “homogeneous field”, please read Is the Flemings left hand rule valid?) The rear end of the conductor (which is farther from us) is connected to the positive terminal of an oscilloscope, the front end to the negative. What will the graph of the induced current (/voltage) look like?
Please look at the picture below:

post-96058-0-36825900-1596448186_thumb.png

There are two crossed lines in it, which I have called “dead lines”.
Whenever the conductor moves through one of those lines, there is no current induced in it. Therefore I called them “dead lines”. But in reality these dead lines are dead planes. The horizontal line I call the main middle plane.
Which plane is the vertical line? It can be any vertical plane which goes through the central point between the magnets. But which one out of the infinite number of them? That depends on the direction of the conductor. Let’s say that the rotating conductor is exactly in the North-South direction. In that case the vertical plane is also in that direction.
 
So, when the conductor is rotating in a homogeneous magnetic field as in the picture above, the induced current will be zero in the four points marked with the Roman numbers (graph below).

post-96058-0-28202400-1596448258_thumb.jpg
 
When a rectangular loop is rotating in a homogeneous magnetic field (figure below), then we have in fact only a second identical conductor which rotates diametrally to the first, because only these two sides of the loop play a role in the current induction (marked with “L” in the figure below). Since the current in the second conductor has the contrary direction, the induced current in the loop will be twice as strong (recall that it is a loop.) The graph above is valid also for this loop, only I have to draw the wave twice as high.

post-96058-0-76960900-1580069399_thumb.png

Edited by MitkoGorgiev
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The Voltage induced in a cable is directly proportional to the rate of change of flux, I think you agree on this. Where you seem to be getting confused is that the current in the circuit is dependent

Instead of trolling, why don't you try to answer my question about the picture from the German textbook?    What is it in the human nature, when one has no arguments, immediately to begin with insults

This is exactly the response you always get from religious extremists. Which these guys are. I've run into their lack of logic and refusal to THINK critically, when discussing the massive errors on Ei

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I have actually done this experiment in Physics 206 and I am here to tell you that sign convention is correct for electrons like GAHD said it would only change if the particles were positrons being positively charged and not negatively charged electrons.

 

fday.png

Edited by VictorMedvil
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You both have misunderstood the thread. It is not about the sign (plus or minus), but about that, in which moment the current is maximal and which moment the current is zero. And this has nothing to do with the sign.

Then you are just wrong then, I have physically done that experiment and it follows Faraday's law.

 

Edited by VictorMedvil
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It is the change in flux that generates the current thus from Zero to point one , the change of flux is at its highest, thus the current is also at its highest as the area interacting with the magnetic field changes greatly as it rotates from a horizontal direction to slightly not horizontal, think of the amount of area interacting from Zero to .1.

Edited by VictorMedvil
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You both have misunderstood the thread. It is not about the sign (plus or minus), but about that, in which moment the current is maximal and which moment the current is zero. And this has nothing to do with the sign.

 

The Voltage induced in a cable is directly proportional to the rate of change of flux, I think you agree on this. Where you seem to be getting confused is that the current in the circuit is dependent on the voltage and the impedance of the circuit. The impedance can be resitive or reactive, or a mixture of both.  In an inductive (reactive)circuit, you have in inductance, and the current lags the voltage. In a capacitive (reactive) circuit you have capacitance and the current leads the voltage. In a purely Resitive circuit the current is in phase with the voltage ie when the voltage peaks the current peaks. In highly reactive circuits with little resistance the current can either lag or lead the voltage dependent on the circuit. In an induction motor the current does indeed lag the voltage, this is in complete agreance with Faradays laws.

 

In the real world when you look closely there is no such thing as a purely resistive or reactive circuit. Even a piece of straight wire has typically 40nH/metre of wire, wires seperarated have capacitance between them, which at very high frequencies or fast switching rates can be an issue. At low frequencies like 50Hz, this small inductance is not worth considering. 

 

Electric motors have a mixture of inductance resistance and to a lesser extent capacitance, which can easily be modelled using complex numbers or lapace transforms. 

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This is one of these cases of the idea of 'A LAW', they are sort of self defining, They are what you define them to be.

 

With Ohms Law, If you define the volt, then by definition you define the value of the amp and the ohm. 

 

1 Volt across 1 Ohm is 1 Amp.

1 Amp is 1 volt / 1 Ohm.

 

So the math is developed to establish that definition, Same applies with faradays law, the sign of a value is the sign of the value as defined by the law, the direction of current flow, or magnetic field is defined it is by convention. It's just like conventional Vs electron flow.

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The Voltage induced in a cable is directly proportional to the rate of change of flux, I think you agree on this. Where you seem to be getting confused is that the current in the circuit is dependent on the voltage and the impedance of the circuit. The impedance can be resitive or reactive, or a mixture of both.  In an inductive (reactive)circuit, you have in inductance, and the current lags the voltage. In a capacitive (reactive) circuit you have capacitance and the current leads the voltage. In a purely Resitive circuit the current is in phase with the voltage ie when the voltage peaks the current peaks. In highly reactive circuits with little resistance the current can either lag or lead the voltage dependent on the circuit. In an induction motor the current does indeed lag the voltage, this is in complete agreance with Faradays laws.

 

In the real world when you look closely there is no such thing as a purely resistive or reactive circuit. Even a piece of straight wire has typically 40nH/metre of wire, wires seperarated have capacitance between them, which at very high frequencies or fast switching rates can be an issue. At low frequencies like 50Hz, this small inductance is not worth considering. 

 

Electric motors have a mixture of inductance resistance and to a lesser extent capacitance, which can easily be modelled using complex numbers or lapace transforms. 

 

Electronics engineer, certainly linear/analogue probably RF.

 

 

 

In the real world when you look closely there is no such thing as a purely resistive or reactive circuit.

 

'In the real world', I think about that idea a lot, I think many theoreticians (particularly in cosmology), forget about that. 

 

Nature simply does not let you do things, it all has it's limits. IN THE REAL WORLD, but if you could have a perfect capacitor charged to 1 volt, and you placed a perfect zero ohm resistor across it, you would get INFINITE power for ZERO time.

 

But in the real world, the capacitor has resistance, and nothing has zero ohm resistance and so on. 

 

I like the limits of nature, what you can't do is more interesting than what you can do, at least it defines what you can do. Engineers (also the 'practical' sciences) understand those limits. Cosmology and Quantum Mechanics -- not so much.

 

I think sometimes: "What if the maximum density of matter is larger than the Schwarzschild radius?"  (I do think it is WAY larger BTW:) 

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I cannot reply separately to all comments, thus I'll say the following: the term "magnetic flux through a loop", which is the basis of the Faraday's law, is simply a huge misconception, something that has nothing to do with the reality. Unfortunately it bears the Faraday's name, but the great Michael Faraday has nothing to do with this "law".

Since it is untrue, such things appear in the electromagnetism as the Faraday paradox: https://en.wikipedia.org/wiki/Faraday_paradox.

And it is not only that. Look at again carefully at the picture from the German textbook (the picture can be found in many textbooks) and please tell me: Does it make sense to you? But please think a few minutes about that picture before you answer me.

The textbook has seven authors, all of them are either electrical engineers or BSc or PhD. And still the picture is a huge lie. Not intentional, but nevertheless, a lie. 

I will not answer to any attack if it doesn't comprise a comment on that picture.

 

https://www.quora.com/What-type-of-electric-current-is-induced-in-a-wire-loop-which-rotates-in-a-magnetic-field/answer/Mitko-Gorgiev

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We have moved from Relativity cranks to electromagnetism cranks, oh joy! Let's see how electromagnetism can be misunderstood now with die hard belief.

Instead of trolling, why don't you try to answer my question about the picture from the German textbook? 

 

What is it in the human nature, when one has no arguments, immediately to begin with insults? Are there psychologists in this forum to answer this question?

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Electronics engineer, certainly linear/analogue probably RF.

 

 

 

'In the real world', I think about that idea a lot, I think many theoreticians (particularly in cosmology), forget about that. 

 

Nature simply does not let you do things, it all has it's limits. IN THE REAL WORLD, but if you could have a perfect capacitor charged to 1 volt, and you placed a perfect zero ohm resistor across it, you would get INFINITE power for ZERO time.

 

But in the real world, the capacitor has resistance, and nothing has zero ohm resistance and so on. 

 

I like the limits of nature, what you can't do is more interesting than what you can do, at least it defines what you can do. Engineers (also the 'practical' sciences) understand those limits. Cosmology and Quantum Mechanics -- not so much.

 

I think sometimes: "What if the maximum density of matter is larger than the Schwarzschild radius?"  (I do think it is WAY larger BTW:) 

In the real world the capacitor has resistance and would limit the current or blow up.

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