Induced Currents (question) (1 Viewer)

[jasonml]

These two questions are taken from DotPoint, from the Motors & Generators chapter. The answers at the back of the book for (a) and (d) are X to Y and X to Y respectively (i.e. they are both X to Y). But i get Y to X for both, when i try to solve it.

Can someone please EXPLAIN to me why its X to Y for each??

 

[cwag]

for these question remember lenzs law, as the induced current will flow in a direction as to oppose the change that caused it...in the case of a) the current will flow in such a direction as to create a north pole on the right side (to oppose magnet) therefore the field lines would be coming out from the middle of the coil and around (on the right side), applying the right hand grip rule we find the current flows from X to Y

in d) same principle. when switch is closed current will flow clockwise..applying the right hand grip rule field lines will be going into the coil on the right side...thus a south pole.....the secondary circuit will create a south pole on the left side to oppose this..applying right hand grip rule current is flowing from X to Y again

 

[munchiecrunchie]

cwag's got it right.

op, are you sure you weren't using your left hand? I do that sometimes.

 

[jasonml]

Okay, i understand (a) now. but i dont understand your reasoning for (d).

The current in the 1st solenoid flows from the positive to negative terminal, so following the diagram and the right-hand-grip rule, wouldnt the north pole be on the right side of the solenoid?

..meaning there would be a north pole created to the left hand side of the 2nd solenoid (Lenz's law), and thus according to the right-hand-grip rule, the current should flow X to Y.

 

[dolbinau]

See diagram:

Isn't this Y-X?

I think they might be using real current not conventional :-/, I'm not sure.

NEVERMIND. I can see now. These diagrams are playing optical allusions on me.

 

[adosh]

can someone please explain this......is a emf induced by a changing magnetic flux( ie cutting flux lines faster or increasing or decreasing strength in magentic flux) or is a emf induced when a conductor just moves in an external magnetic field,,such as say a flat metal sheet,, or a wire moving through magnetic field lines at ocnstant speed...or is it both???????

 

[adosh]

lol this is what i meant, ,,, imagine a magnetic flux pointing up.......now imagine i hold a wireand i move it perpendicular to the flux to the right at CONSTANT velocity. as the wire continues to move in the flux is an emf genetrated....if yes ,,then is this considered a change in flux??