# Confusion about the flow of current in a motional emf system

Down below is a conductive bar of length $$L$$ moving on two conductive rails in a magnetic field. I have a couple of questions regarding the flow of current in such a system.

How does the current flow through the closed circuit if the length of the bar $$L$$ is larger than the width of the rails $$l$$ ? I'm curious to know what is happening at the ends of the bar in particular. Do the electrons reach them and make a U-turn or something?

• The energy doesn't flow in the electrons. It flows in the electromagnetic field surrounding the conductors (and a little bit of it flows on their inside because of skin effect). Energy flow is one of the limits of the classical electron-flow model in electrical conductors. It gives us the wrong intuition about what is happening. If you want to get the correct understanding, then you have to learn about Maxwell's equations and the Poynting vector. Commented May 6, 2023 at 16:07
• @Flatterman you're just spreading the misconception popularized by youtubers that the energy flux vanishes in a perfect carrying current conductor. If you,want to learn.the truth, have a look at non eq. thermodynamics. There is definiteluy an energy flux due to moving charges. Commented May 6, 2023 at 17:12
• @untreated_paramediensis_karnik Please note my remark "and a little bit of it flows on their inside because of skin effect". You are welcome to analyze energy flow in a transformer, or, if that is not enough... explain the energy flow of 1kW/m^2 on Earth's surface that is caused by solar radiation. There are certainly no wires involved there. Commented May 6, 2023 at 17:32
• All emf's are "induced." The normal term for the kind of emf you are talking about (due to the Lorentz force of a constant magnetic field on a moving circuit element) is "motional emf."
– Buzz
Commented May 7, 2023 at 6:08
• @untreated_paramediensis_karnik Electrons moving at a few um per second (the drift speed in a typical metal) carry very little kinetic energy. Commented May 8, 2023 at 2:59

All along the moving rod, including the ends beyond the rails, its charges experience the magnetic Lorentz force, $$\vec F=q\vec v \times \vec B$$. The free electrons are urged towards the end of the rod furthest from us (the viewer).
These 'chargings of the ends' will happen very quickly. [The unbalancing of charges will give rise to electric fields and electric Lorentz force ($$\vec F=q\vec E$$) on the free electrons in the ends of the rods that will quickly counterbalance the magnetic Lorentz forces on them so no more charge will accumulate.]