faraday's law

[broegger]

by faraday's law induced current in a conducting loop is caused by changes in magnetic flux through that loop..
now, if you move a conducting loop through uniform magnetic field (fixed magnitude and direction) there is an induced current even though there is (apparently) no change in magnetic flux (the loop area stays the same and the magnetic field is uniform).. how come?

(this same question applies to the "faraday disk dynamo", if anyone is familiar with that)

[retupmoc]

Has the angle between the normal to the conducting loop and the magnetic field changed at all?

[broegger]

no, i'm aware that this would correspond to a change in magnetic flux.. imagine a rectangular loop moving perpendicular through a uniform magnetic field or a circular disk rotating around a fixed axis (faraday's dynamo)

[Doc Al]

Originally posted by broegger
by faraday's law induced current in a conducting loop is caused by changes in magnetic flux through that loop..
now, if you move a conducting loop through uniform magnetic field (fixed magnitude and direction) there is an induced current even though there is (apparently) no change in magnetic flux (the loop area stays the same and the magnetic field is uniform).. how come?

Why do you think this true?

[broegger]

my book states that there is an induced emf everytime a conductor moves relative to a magnetic field.. but in the situations described this (as far as i can see) doesn't imply a change in magnetic flux.. e.g. in faraday's disk dynamo a conducting disk rotates about a fixed axis in a uniform magnetic field which causes an induced current - but how does the flux change in this situation?

[Doc Al]

You had made the statement that a conducting loop moving through a uniform magnetic field will have an induced current. I don't believe that's true.

You are also asking about Faraday's disk. That one is subtle and I don't think I can do it justice. (I will think about it.) Here's a website that gives it a shot. http://www.madsci.org/posts/archives/sep99/937493491.Ph.r.html

[broegger]

Thanks for answering. I can see i'm not the only one troubled by the disk dynamo :) on closer considerations i agree that there cannot be a current in the 'rectangular loop'-situation I described.. but the disk dynamo is still a mystery