Electromagnetic induction silly question

  • Thread starter crx
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  • #1
crx
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I was thinking at electromagnetic induction in two paralel wires...I searched some websites about this and i found out that acording to Lenz's law :"An induced current is always in such a direction as to oppose the motion or change causing it". Acording to this an induced current is opposig the original (inductor) current (180 phase shift).. So i did a similar experiment. I sent square pulses and a sin wave in a wire parallel to another wire and hooked them up to an oscope. I saw that actually the induced signal is in phase with the original signal. So what i learned is that an induced current is is the same dirrection with the original current... Even when i approached a magnet to a coil the induced current had the same direction with the imaginarry current that would make up the magnetic field (in respect with the N-S poles) of the magnet. This doesn't seem to listen to the Lenz's law, so i guess i did something wrong...
Could some of you do some quick experiments to see exactly what the results are?
thanks
 

Answers and Replies

  • #2
Doesn't Lenz's Law only apply to inductive coils? It just doesn't seem logical that parallel wires would be out of phase. The phase is variable but electromagnetic propagation is constant.
 
  • #3
crx
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Doesn't Lenz's Law only apply to inductive coils? It just doesn't seem logical that parallel wires would be out of phase. The phase is variable but electromagnetic propagation is constant.
Even if you have two coils made of one single loop each, put close together (same axis) and if there is a rising current in one loop the induced current sould have the same dirrection (in phase). And of course there is a repulsive force too. Everywhere i searched they showed that the induced current is opposing the inductor current, and in this way you could explain the repulsive force as two opposing currents interraction. But my observations are differnt than those...so probably im doing something wrong....
 
  • #5
crx
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What's funny is that i read these postings and some here can talk forever about time dilatation, time travel, and bending space, but nobody can really imagine the process of electrogantic induction, wich is all around our life (virtual photons ...right)....Is this really so abstract? Its accessible for everybody to experiment with and still we are in doubt ...
 
  • #6
Drakkith
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Acording to this an induced current is opposig the original (inductor) current (180 phase shift)..
Isn't the induced current caused by the magnetic field or flux? The motion of the current is getting energy from the flux and is opposing it by taking energy from it to move. Or at least thats what I got from my reading.
 
  • #7
crx
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Isn't the induced current caused by the magnetic field or flux? The motion of the current is getting energy from the flux and is opposing it by taking energy from it to move. Or at least thats what I got from my reading.
This is what i learned in school me too... that the induced current will produce a magnetic flux that will oppose the inductor flux... I just wanted to see myself how this stuff works in reality and i observed that both currents will produce a magnetic flux of the same orientation...One of the most simple and obvious way to check this phenomen is by considering induction between two parallel conductors..
I know that this its considered by most of us a well studied phenomena, but is the least understood and the one reason for this is that we cannot comprehend why the induced current is in opposite direction...
When we slide a permanent magnet on a nonferomagnetic conductor surface we can see exactly that there is a force opposing movement so we guess that the Eddy current with its magnetic field should oppose the permanent magnet's field, but is this the reality? I would like to know...
 
  • #8
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This is what i learned in school me too... that the induced current will produce a magnetic flux that will oppose the inductor flux... I just wanted to see myself how this stuff works in reality and i observed that both currents will produce a magnetic flux of the same orientation...One of the most simple and obvious way to check this phenomen is by considering induction between two parallel conductors..
I know that this its considered by most of us a well studied phenomena, but is the least understood and the one reason for this is that we cannot comprehend why the induced current is in opposite direction...
When we slide a permanent magnet on a nonferomagnetic conductor surface we can see exactly that there is a force opposing movement so we guess that the Eddy current with its magnetic field should oppose the permanent magnet's field, but is this the reality? I would like to know...
This is not quite right but it is a common point of confusion.
The induced flux will oppose the variation of the inductor flux.
If the inductor flux is decreasing, the induced one will be in the same direction.
It direction of the currents depends on geometry.
 
  • #9
Drakkith
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The electrons in the current have to get their energy from somewhere. I'm guessing that when they say that the current opposes whatever causes it, they mean that it's like hitting a volleyball or something. You move your hand and when it hits the volleyball the energy is transferred into it. It opposes the source thats causing the movement but still moves the the direction of your hand movement.
 
  • #10
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Lenz law is not about electrons or the mechanism that produces the current. It is a simple way to determine the direction of the induced field and induced current. The induced field can add up to the original field (when this last one decreases) or subtract from it (when it increases).
When you suddenly turn off the current through a coil with large inductance, the induced current is in the same direction as the original one and can be much larger.
 
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  • #11
crx
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Lenz law is not about electrons or the mechanism that produces the current. It is a simple way to determine the direction of the induced filed and induced current. The induced field can add up to the original filed (when this last one decreases) or subtract from it (when it increases).
When you suddenly turn off the current through a coil with large inductance, the induced current is in the same direction as the original one and can be much larger.
Salut Nasu!

Exactly this is what i realized after i checked this out on my own ..Its very sad that most of the information regardind this is faulty.. Look any website (or even some school books) about this subject. Even if they give the right interpretation of the law ("oposing the variation of the flux" ...right now I'm thinking that superconducting levitation shows well this effect ...) so when they about to show a drawing that will be most of the time wrong....
So the verdict is that the induced current in two paralell conductors will have the same direction as the inductor current .
 
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  • #12
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So the verdict is that the induced current in two paralell conductors will have the same direction as the inductor current .
Salut Crx.
If you mean the current induced by one current carrying conductor in a second conductor, the verdict is: it depends. It depends on what the induced current is doing. If the current in the first wire is constant, there is no induced current. If the current increases or decreases there will be an induced current whose direction depends on what exactly the first current is doing: increasing or decreasing. The currents may have the same direction in one case and opposite in the other. Which on is which depends on geometry.
 

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