Jayant

A different way exists to compute induced voltages: it's the vector potential A

http://en.wikipedia.org/wiki/Magnetic_potential

less concrete than B, less often useful than d(flux)/dt, but sometimes invaluable, especially when the flux makes little sense.

 

It's convenient when Biot-Savart can compute it as:

http://de.wikipedia.org/wiki/Biot-Savart-Gesetz (the en fr es pt it articles have only B, not A)

dA( r) = (µ/4pi)*(I*dL)/|r| (here A and dL are vectors, r if you want)

and then the induced electric field is just -dA/dt. Nice and simple to evaluate parasitic couplings. It belongs to the computational toolbox of electromagnetic compatibility.

 

Now, your wire passes by the coil's axis if I get it properly, and is perpendicular to the coil's axis.Just because the created E is parallel to the produced A which is parallel to I*dL, we can tell that the coil's symmetry prevents it from inducing an electric field in said wire.

 

The parts of the turns symmetric above and below the plane conduct the same current at the same distance to the target wire and the same cosine but in opposite directions, so each complete turn has zero net effect.

 

Again, we find that if some current flows through a closed circuit that contains the described target wire, it will result only from the rest of the circuit. This time, we can say more precisely that any voltage would be induced elsewhere in the circuit, not in the described wire, and that the return circuit would have to be above or under the plane of symmetry to get an induced voltage.

 

The flux wouldn't give naturally an answer as detailed, the induction B not as simply.

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I realize only now that you've written "the field is along X", and this is an impossibility. The field and the induction make closed loops, so they have to change their direction. My answers hold for a magnet oriented along X.

 

A field approximately along X would be possible within an electromagnet, not outside. For instance in Helmholtz' coils

http://en.wikipedia.org/wiki/Helmholtz_coil

or within a long solenoid.

 

In this case as well, the return circuit would decide everything.

Thanks a lot

Jayant

A different way exists to compute induced voltages: it's the vector potential A

http://en.wikipedia.org/wiki/Magnetic_potential

less concrete than B, less often useful than d(flux)/dt, but sometimes invaluable, especially when the flux makes little sense.

 

It's convenient when Biot-Savart can compute it as:

http://de.wikipedia.org/wiki/Biot-Savart-Gesetz (the en fr es pt it articles have only B, not A)

dA( r) = (µ/4pi)*(I*dL)/|r| (here A and dL are vectors, r if you want)

and then the induced electric field is just -dA/dt. Nice and simple to evaluate parasitic couplings. It belongs to the computational toolbox of electromagnetic compatibility.

 

Now, your wire passes by the coil's axis if I get it properly, and is perpendicular to the coil's axis.Just because the created E is parallel to the produced A which is parallel to I*dL, we can tell that the coil's symmetry prevents it from inducing an electric field in said wire.

 

The parts of the turns symmetric above and below the plane conduct the same current at the same distance to the target wire and the same cosine but in opposite directions, so each complete turn has zero net effect.

 

Again, we find that if some current flows through a closed circuit that contains the described target wire, it will result only from the rest of the circuit. This time, we can say more precisely that any voltage would be induced elsewhere in the circuit, not in the described wire, and that the return circuit would have to be above or under the plane of symmetry to get an induced voltage.

 

The flux wouldn't give naturally an answer as detailed, the induction B not as simply.

----------

 

I realize only now that you've written "the field is along X", and this is an impossibility. The field and the induction make closed loops, so they have to change their direction. My answers hold for a magnet oriented along X.

 

A field approximately along X would be possible within an electromagnet, not outside. For instance in Helmholtz' coils

http://en.wikipedia.org/wiki/Helmholtz_coil

or within a long solenoid.

 

In this case as well, the return circuit would decide everything.

A different way exists to compute induced voltages: it's the vector potential A

http://en.wikipedia.org/wiki/Magnetic_potential

less concrete than B, less often useful than d(flux)/dt, but sometimes invaluable, especially when the flux makes little sense.

 

It's convenient when Biot-Savart can compute it as:

http://de.wikipedia.org/wiki/Biot-Savart-Gesetz (the en fr es pt it articles have only B, not A)

dA( r) = (µ/4pi)*(I*dL)/|r| (here A and dL are vectors, r if you want)

and then the induced electric field is just -dA/dt. Nice and simple to evaluate parasitic couplings. It belongs to the computational toolbox of electromagnetic compatibility.

 

Now, your wire passes by the coil's axis if I get it properly, and is perpendicular to the coil's axis.Just because the created E is parallel to the produced A which is parallel to I*dL, we can tell that the coil's symmetry prevents it from inducing an electric field in said wire.

 

The parts of the turns symmetric above and below the plane conduct the same current at the same distance to the target wire and the same cosine but in opposite directions, so each complete turn has zero net effect.

 

Again, we find that if some current flows through a closed circuit that contains the described target wire, it will result only from the rest of the circuit. This time, we can say more precisely that any voltage would be induced elsewhere in the circuit, not in the described wire, and that the return circuit would have to be above or under the plane of symmetry to get an induced voltage.

 

The flux wouldn't give naturally an answer as detailed, the induction B not as simply.

----------

 

I realize only now that you've written "the field is along X", and this is an impossibility. The field and the induction make closed loops, so they have to change their direction. My answers hold for a magnet oriented along X.

 

A field approximately along X would be possible within an electromagnet, not outside. For instance in Helmholtz' coils

http://en.wikipedia.org/wiki/Helmholtz_coil

or within a long solenoid.

 

In this case as well, the return circuit would decide everything.

thanks for very good reply

Jayant

Can anybody explain me in which direction the electic current will flow in a cunductor kept in a changing electomagnetic field as described below,

A thin wire shape conductor is kept perpendiculer to the direction of field generated by an electromagnet. Assum that magnetic field is along the 'x' axis, conducter is placed along the 'y' axis

now if we change the current in electromagnet coil or put the current on or off than it will change the magnetic flux and a current will be generated in conductor.

We all know the fleming's low and lenz's law, as per my understanding of these laws, current can flow either in 'y' to '-y' derection or from '-y' to 'y' direction which will generate a thrust in z or -z direction depending on the direction of current.

Can we predict the direction of current in cunductor before changing the magnetic flux ?

or it is just a matter of chance which will decide the direction of currrent ?

thanks in advance

Jayant