1. Aug 29, 2009

### DrDanger

Okay so i just want to make sure i got this right because its a kind of confusing topic for me. So eddy currents are caused because when there is a motion (with a conducting surface) through a magnetic field a current is induced? and because there is a current there is also a magnetic field due to that current which opposes the original magnetic field and causes it to slow down?! Also when people are generating electrical energy by rotating a square/circle loop through a magnetic field do eddy currents slow you down? also I realize by cutting slots and other means you can reduce eddy currents. Thanks for the answers, and i hope my question was clear

2. Aug 29, 2009

### Bob S

You got it pretty much right. But the eddy currents are only induced in a conducting material if the magnetic field is changing with time, or if a conducting material is moving through a magnetic field that is non-uniform (fcn of x, y, z), or rotating in a constant magnetic field.

Last edited: Aug 29, 2009
3. Aug 29, 2009

### DrDanger

Why does the magnetic field have to be non-uniform?

4. Aug 29, 2009

### negitron

Because something has to change over time; if the conductor moves through a uniform magnetic field, it's functionally static.

5. Aug 29, 2009

### DrDanger

Ahh makes sense now its becuase there has to be a flux right?, but there is no such thing as a uniform magnetic field right? except inside solenoids, but even then its not exactly uniform right?

6. Aug 29, 2009

### Bob S

The basis for eddy currents is the integral form of Faraday's Law

E dl = -(d/dt) ∫B·dA

where ∫dl is around the perimeter of surface A.

and J = σ E So
" Ahh makes sense now its becuase there has to be a changing flux right?" Note the d/dt in Faraday's law.

7. Aug 29, 2009

### DrDanger

Thank you for the correction, and yes that is what I mean. Thanks for all the help guys, and the fast responses!