What is Steady State in Bar and Rail Magnetic Field Problems?

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Discussion Overview

The discussion revolves around the concept of "steady state" in the context of bar and rail magnetic field problems, particularly focusing on the implications of steady state for the motion of a bar on rails, the induced current, and the calculation of velocity. Participants explore the definitions and conditions that characterize steady state, as well as the mathematical relationships involved in solving related problems.

Discussion Character

  • Homework-related
  • Conceptual clarification
  • Mathematical reasoning

Main Points Raised

  • One participant questions the meaning of "steady state" and whether current will be induced due to acceleration, suggesting a relationship between forces acting on the bar.
  • Another participant proposes that steady state refers to a condition where the velocity is constant, indicating that acceleration (\(dv/dt\)) is zero.
  • A participant confirms agreement with the previous calculation of velocity, indicating a shared understanding of the problem setup.
  • One participant emphasizes the need to specify the direction of the velocity vector, suggesting that it should align with the direction of acceleration due to external forces once steady state is achieved.

Areas of Agreement / Disagreement

Participants generally agree on the interpretation of steady state as a condition of constant velocity, but there is some discussion about the specifics of direction and the calculations involved. No consensus is reached on the overall approach to the problem or the correctness of the calculations.

Contextual Notes

There are limitations regarding the assumptions made about the system, such as the length of the bar relative to the rails and the forces acting on the bar. The discussion does not resolve these assumptions or the implications they may have on the calculations.

Who May Find This Useful

This discussion may be useful for students or individuals studying electromagnetism, particularly those dealing with problems involving magnetic fields and motion in conductive systems.

dimpledur
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Homework Statement


Couple questions regarding the following image:
Untitled-3.png

What is meant when the problem states that "steady state can be achieved"? Will current be induced in this set up due to the acceleration to the right? For example, would I go Fg1-Fg2-Ffriction= Fmagnetic, and from there calculate the velocity of the bar at steady state? Will the bar even be moving to the right in steady state?
I can't seem to find any notes regarding this. How does one determine the direction? I found this type of question easier when there was an actual current through the system..

Any help is appreciated.
 
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Okay, I've come to realize steady state refers to the velocity, meaning dv/dt. Could someone please check my work for the following question solving for the velocity of the bar.

Please note that the question states the bar is 1m long, but the rails are only 0.75m apart. l would equal 0.75 for this question then right?

m1g+μmg+IlB=m2g

note: I= lemfl/R=Blv/R

thus, v=gR(m2-μm-m1)/(l^2*B^2)

v=[(9.81)(1)(10-0.5-5)]/(0.75^2*0.5^2)
v=313.9 m/s directed along the rail.

Did I do that right? Thanks.
 
Last edited:
I got the same.
 
I wouldn't merely state "on the rail" as a sense of direction for the velocity vector. You need to distinguish between right and left. As for determining the direction, determine which direction the bar will accelerate due to the external forces, and once steady state is achieved, the velocity vector will be in the same direction. Steady state in this sense merely means [tex]\frac{dv}{dt}=0[/tex].
 

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