magnetic induction question - Page 1
Forum section: electronics / beginners

author: fonograph
author_rank: Frequent Contributor
timestamp: December 16, 2018, 04:34:37 am
content: I know that moving conductor in magnetic field will cause current to flow in that conductor.But what happens if the conductor is moving perfectly straight,parallel to the direction of magnetic field,its cruising along the lines.Will that cause current to flow too? I saw video about induction that says cutting the magnetic lines causes the current flow,does that mean not cutting the line,going alongside them,will no induce current?

author: cdev
author_rank: Super Contributor
timestamp: December 16, 2018, 04:48:57 am
content: there would be positions and orientations where a moving electromagnetic field did not induce any voltage in a conductor, that is the same thing as equilibrium, this would be called a null in its pattern.Perpendicularwires in an open space only exhibit very low amounts of coupling to one another.

author: ejeffrey
author_rank: Super Contributor
timestamp: December 16, 2018, 05:34:11 am
content: That is correct, moving parallel to the applied field will not introduce an emf or current flow. The force on an electron is V x B. If V and B are parallel the force is zero.In addition, In the case of a wire (as opposed to an arbitrary shape), if the velocity or the magentic field is parallel to the wire, the emf will be perpendicular to the wire, and won't cause any current to flow along the wire.Keep in mind that when we talk about magnetic induction, wires are normally loops. So you have to consider the entire loop to see if there is induced current.

author: fonograph
author_rank: Frequent Contributor
timestamp: December 16, 2018, 05:40:33 am
content: What is V and B?

author: IanB
author_rank: Super Contributor
timestamp: December 16, 2018, 05:48:32 am
content: A slightly related question:Suppose there is a transformer which has a closed magnetic loop inside the core (e.g. a toroid). I been given to understand that the (changing) magnetic field lines should intersect the conductor for a current to be induced. If, in a toroid, the magnetic field lines are concentrated within the core, how is current induced in the secondary windings of a toroidal transformer? If you passed a DC current through a winding to turn the transformer into an electromagnet, would there be any detectable magnetic field on the outside? If so, where would the north and south poles be?

author: IanB
author_rank: Super Contributor
timestamp: December 16, 2018, 05:53:42 am
content: Quote from: fonograph on December 16, 2018, 05:40:33 amAn answer which tells you nothing is that V and B are vector quantities that define the magnitude and direction of the V and B fields. V x B is the cross-product between them, which is a mathematical operation between two vectors that produces a third vector perpendicular to the original two vectors.For an answer that tells you something more meaningful, I will defer to someone else.

author: Brumby
author_rank: Unknown
timestamp: December 16, 2018, 10:30:45 am
content: Quote from: fonograph on December 16, 2018, 05:40:33 amV is the velocity of a conductor.B is the strength of the magnetic field.Both are vectors and theirvectorproduct is used in the calculation of the potential generated in a conductor. These are not the only factors used - but I'm not about to go into detail here.

author: rfeecs
author_rank: Frequent Contributor
timestamp: December 16, 2018, 06:44:12 pm
content: Quote from: IanB on December 16, 2018, 05:48:32 amBecause you don't need the magnetic field to cut across or intersect with the conductor for a current to be induced. The changing magnetic field produces an electric field all around it in space. The electric field causes the current. This is Faraday's law of induction.

author: fonograph
author_rank: Frequent Contributor
timestamp: December 17, 2018, 09:33:50 pm
content: Quote from: rfeecs on December 16, 2018, 06:44:12 pmBut what if its magnetic field between two magnets? The field strenght doesnt change with distance and the lines are straight. So if you move up and down between two magnets that are above and bellow,and the magnets are much wider than the conducting object between them.Then you are neither intersecting lines nor moving to area with different field strenght.

author: rfeecs
author_rank: Frequent Contributor
timestamp: December 17, 2018, 10:36:13 pm
content: Quote from: fonograph on December 17, 2018, 09:33:50 pmAs has been said, if the wire is parallel to the magnetic "lines of force", then it will not induce a current.If the magnetic flux through a loop doesn't change, then it will not induce a current in the loop.You might want to look up the Lorentz force as well as Faraday's law:https://en.wikipedia.org/wiki/Lorentz_forcehttps://en.wikipedia.org/wiki/Faraday%27s_law_of_induction

author: MrAl
author_rank: Super Contributor
timestamp: December 21, 2018, 02:44:51 pm
content: Quote from: fonograph on December 16, 2018, 04:34:37 amHello,The current that flows depends not only on the field strength but also on the orientation of the field and the movement relative to the wire.Because it depends also on the orientation, there is a certain orientation that will cause maximum current flow and another orientation that will not cause any current flow. Mathematically this is obtained from what is known as the "Cross Product".The cross product produces a value like any multiplication, but it also produces a direction. If the direction is not along the wire length then there will not be maximum current, and if the direction turns out to be perpendicular, there will be zero current.There is even a possibility that there will be current flow across the diameter of the wire rather than along the length but that's not usually considered too often with the direction along the wire being the direction most focused on for most problems.To find out how this works, you'd have to look up the cross product and maybe a little vector algebra. The vectors make it possible to state problems not only in terms of amplitude, but also in terms of direction and that is needed because magnetic fields have orientation which is synonymous with direction.If you dont want to do that, then just realize that if you have a wire laying flat on a wood table and a moving field and you rotate the orientation of the wire like the hand of a clock as the field is moving past it (or along it) you will see the current go up and down as you rotate the wire. It will go up to some maximum and down to zero, and then reverse maximum and back down to zero. The field needs to keep moving though relative to the wire. Of course this assumes a closed path for the wire so current can flow, so you'd need a return path that is far enough away from the field to not be affected much or else you'd have to take that into account too.