Another problem from magnetism

  • Thread starter Kolahal Bhattacharya
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In summary, the conversation discusses finding the electric field when an alternating current flows through a long wire and returns through a coaxial conducting tube. The problem was solved using the equation ∫E∙dl = (-dΦ/dt) and assuming B=μn I cos wt. There is a discussion about neglecting the current returning through the conducting tube and justifying the use of Ampere's law. It is mentioned that the B field must be 0 outside the tube and that Ampere's loop is a circle within the tube.
  • #1
Kolahal Bhattacharya
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Homework Statement



An alternating current I cos wt flows down a long wire and returns along a coaxial conducting tube of radius a. Find E assuming E→0 at ∞.

Homework Equations





The Attempt at a Solution



I did the problem from Griffiths but have some problem to understand the physical situation. I did using ∫E∙dl = (-dΦ/dt) and proceeded straight away as B=μn I cos wt.
How much it is justified as I am simply neglecting the current returning through the conducting tube?
 
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  • #2
B comes from Ampere's law, which includes only the current within the loop.
The current in the outer tube is outside the loop.
 
  • #3
How do you know where to construct Ampere's loop?At first you are to justify that the B field must be 0 outside the tube.
 
  • #4
Ampere's loop is a circle within the tube, where you need to know B.
The field outside the tube ils irrelevant.
 

1. What is magnetism?

Magnetism is a physical phenomenon that is caused by the presence of magnetic fields. These fields are produced by moving electric charges and can attract or repel other magnetic materials.

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3. What are the main types of magnets?

The main types of magnets are permanent magnets, which retain their magnetism over time, and electromagnets, which are created by passing an electric current through a wire wrapped around a magnetic core.

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