Zero Induced EMF: Find Rate of B Change for Problem 9

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Homework Help Overview

The discussion revolves around a problem involving electromagnetic induction, specifically focusing on the conditions required to achieve zero induced electromotive force (emf) in a circuit when a wire moves in a magnetic field. The original poster seeks to determine the rate of change of the magnetic field (B) necessary to maintain this condition while the wire moves at a specified velocity.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • The original poster expresses confusion regarding how a velocity, electric field, and length can coexist without resulting in an induced emf. They reference the equation for induced emf and indicate a lack of understanding about the conditions for zero induced emf.
  • Some participants suggest equating two expressions for emf to explore the relationship between the rate of change of the magnetic field and the motion of the wire.
  • There is a mention of the concept of 'rate of change' of the magnetic field, prompting further exploration of its implications.

Discussion Status

The discussion is ongoing, with participants exploring the necessary conditions for zero induced emf. Some guidance has been offered regarding the mathematical relationships involved, but there is no explicit consensus on the approach to take or the underlying assumptions that need clarification.

Contextual Notes

Participants note specific parameters from the original problem, such as the length of the wire and the initial magnetic field strength, indicating these may be relevant to the calculations being discussed. There is also a reference to the original problem's setup, which may influence the understanding of the current question.

CD135
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Homework Statement


Question I need help with: If wire AB of problem 9 moves with a velocity of 50.0 m/s to the right, at what rate should B change when the wire is at a distance of 5.00 cm from the left end of the loop, such that there will be no induced emf in the circuit? Answer: 300 T/s

Problem 9: (I don't know if this information is needed to solve the question above so I'm listing it here anyway)
The wire AB in the diagram moves to the right with a velocity of 25.0 cm/s. If l = 20.0 cm, B = 0.300 T, and the total resistance of the circuit is 50.0 Ω, find (a) the induced emf in wire AB, (b) the current flowing in the circuit, and (c) the direction of the current.Diagram is attatched

Homework Equations


emf=Blv
emf=change in flux/ change in time

The Attempt at a Solution


I don't understand this question. I have been trying for a very long time and I am very lost. If there is a velocity, electric field, and length, how could there ever be zero induced EMF? I was able to get question 9 as emf=Blv, very straight forward and I understand how the equation is derived. I'm clearly missing something here but I cannot figure out what.
 

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Any help would be appreciated. I cannot find any information online or in the textbook to help me come up with any sort of solution. Thank you in advance!
 
CD135 said:
emf=Blv
emf=change in flux/ change in time
These two emfs will be opposing each other such that resultant emf will be 0.
Write mathematical equations for each and simply equate them.
CD135 said:
at what rate should B change
This asks you about 'rate of change' of magnetic field. Ring any bells?
CD135 said:
Answer: 300 T/s
Right.
 
CD135 said:
(I don't know if this information is needed to solve the question above
CD135 said:
l = 20.0 cm, B = 0.300 T
This is needed.
 

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