How to find speed with Faraday's law

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Homework Help Overview

The discussion revolves around a physics problem involving a metal rod sliding on a rail within a uniform magnetic field. The problem includes determining the force required to maintain a constant speed and calculating the work dissipated in a resistor after the rod is released.

Discussion Character

  • Exploratory, Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants discuss the application of Faraday's law and the relationship between magnetic fields and induced electromotive force. There are attempts to clarify the change in area as the rod moves and how it relates to the magnetic flux. Some participants express uncertainty about the variables involved in the equations.

Discussion Status

The discussion is ongoing, with participants exploring different aspects of the problem. Some guidance has been offered regarding the concepts of magnetic force and the relationship between the area and magnetic flux, but no consensus has been reached on specific calculations or methods.

Contextual Notes

There is a request for a figure to better understand the problem setup. Additionally, participants are encouraged to show their detailed work to facilitate further discussion and verification of their reasoning.

Jacobs
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Homework Statement


A metal rod can slide on a rail without any friction in the presence of uniform magnetic field of B=1T which is perpendicular to the plane of the paper.The distance between the tracks is d=0.1m and the resistance given is R=0.1 ohm.The resistance of the rail is negligible and the mass of the rod is m=20g. A)How much force must be on the road exerted in order to move it with a constant speed of v=10m/s? B)The rod has been moved for t=2s and then it is released.How much work is dissioated on the resistor till the rop will stop?

Homework Equations


F=IBl=B^2*l^2*v/R

The Attempt at a Solution


According to first formula F=1 but for B i have no idea
 
Last edited:
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Welcome to the PF.

Could you please post the figure that goes with this question? It sounds like a classic sliding rail changing the total B*dA, but it's hard for me to be sure from the text of your post. Thanks. :smile:
 
1st one
 

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You might start here. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html

The rails and the rod and resistor make an electric loop. You can find the area of that loop if you know the length, but for this problem, you are interested in the Change in the area when the rod moves. Since Phi = B*A, phi can change if B changes or (in your case) when A changes. It doesn't do a whole lot of good to have some formulas, unless you have an idea of where they come from. Then you'll understand which ones to use.
 
so formula is BdeltaA/delta(t) but still have no idea about how find find change in the area
 
Answer of B is 2?
 
Jacobs said:
so formula is BdeltaA/delta(t) but still have no idea about how find find change in the area
The motion of the movable rod changes the area.
Jacobs said:
Answer of B is 2?
Please always show your detailed work so we can check it. Thank you.
 
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