posted by Promise .
A metal rod of length (L) moves with velocity (v), perpendicular to its length, in a magnetic field B, which is perpendicular to both the rod and its velocity. If the length of the rod is doubled, what happens to the electric field in the rod?
Since it is a conducting metal, there is no net E field. Negative charge accumulates at one end of the rod, while the rod moves, but there is also a magnetic force on electrons that opposes the field created by displaced electron charge.
If a closed circuit were formed, so that electrons were free to move in a current loop, the EMF (E-field times length) would double if the length of the rod doubled. The E-field would stay the same. I believe the value would be B * (V/c), but am not sure.