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RES: [femm] How to define the current in a circuit



Dear Zhang

 

As a matter of fact, you should define the vector current density, as follows:

If the magnetic circuit is on the x-y plane, your vector current density is J = |J|k,where k is the unit vector in the z-direction. In this case, |J|= Jz = I/S, where I is the total current in thecoil and S is its cross section surface. Therefore, you must supply a Jplus current density, Jplus =|J| A/m^2 in one side of the circuit and Jminus = -|J| Am^2, in the other side of the circuit. Remember that the electric current density is continous along the coil.

Yours sincerely.

 

Prof. Francisco Tejo

 

P.S.: Perhaps, the figure below may be of some help to you.

 

                                            Y |

                                              |

                                            _____

                                           +|   |-

                                   Jz(plus)+| C |- Jz(minus)

                                           +| o |-

                             ______________+| r |-__________________ X

                                           +| e |-

                                           +|   |-

                                           +|   |-

                                           +|   |-

                                           +|   |-

                                            _____

                                              |

                                              |

-----Mensagem original-----
De: Lefu Zhang [mailto:lefu_zhang@xxxxxxxxx]
Enviada em: Thursday, September 18, 2003 3:52 AM
Para: femm@xxxxxxxxxxxxxxx
Assunto: [femm] How to define the current in a circuit

 

Dear friends,

 

I am a new comer in using FEMM3.3. When I was learning

the example of DCMagnet, I was a little confused about

the definition of current in the circuit. Due to the

2-D effect, we have to draw two parts for one

excitation coil, and we have to define same current

value "plus" and "minus" circuit for them. WhatI want

to know is that the value of the current should be the

total current or half of the total current in the

practical coil. Any help will be appreciated.

 

Thanks

 

Lefu Zhang

 

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