# What equation should be used when this conductor passes a magnetic field?

A large thick copper wire(or bar if you like,) passes a magnetic field. What formula is best to calculate the $EMF$ here?

$$\epsilon = \frac{\Delta \Phi \ }{\Delta t}$$

or,

$$\epsilon = -vBL$$

Example:

This image is used to demonstrate Lorentz force, however, it can be used to illustrate my question, lets imagine the conductor in the middle is moving and its passing the magnetic field, when it reaches that point in the diagram it is connected to a circuit to allow current to flow.

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Closely related to physics.stackexchange.com/questions/105717/motional-emf-and-emf. –  dmckee Apr 2 '14 at 20:28