Re: Induction and moving rod on a U-shaped conductor

[Leigh Palmer <palmer@sfu.ca>]

> When a conducting rod is moving in a uniform magnetic field (rod, magnetic
> field, velocity mutually perpendicular) charge accumulation establish at the
> ends of the rod. If the rod slides along a stationary U-shaped conductor, an
> induced current is established around the circuit.
> My question is about the motion of the elkectrons of the U-shaped conductor
> when these electrons reachthe moving rod: Do the electrons from the U-shaped
> cpnductor go inside the rod?

Yes, they do, but it is physically impossible to distinguish one
electron from another, so my answer is really mystical; there's
no way to verify it empirically. For the purposes of high school
physics teaching I'd go ahead and answer "Yes".

> An excellent analysis about the motion of electrons has been made by
> Young-Freedman (University Physics- ninth edition pg. 953) But they don' t
> mention what happens if the electrons of U-shaped conductor reach the moving
> rod.
>
> I have another question about the electrons' motion in the U-shaped
> conductor and rod. Suppose that the rod has big length, bigger than the
> opening of the U-shaped conductor so its ends exceed  the U-shaped
> conductor. What happens with the electrons? Do they accumulate at the point
> of the rod, where the rod meets tha U-shaped conductor? If so, why does this
> happen? Don't forget that the whole rod is inside a uniform magnetic

They flow into and out of the rod at the contact points, and
charge builds up on both of the ends sticking out. This question
is easier to analyze if one merely considers the forces acting on
the electrons in the rod's frame of reference. The overhanging
electrons are not accelerating, but there is a magnetic force
acting on them due to the moving magnetic field.therefore they
are in an electric field, and that field is due to charge
accumulations on the surface of the rod.

Leigh