Magnetic Field due to Opposing Coils

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Homework Help Overview

The discussion revolves around the magnetic field produced by two coils connected with magnetic fields pointing in opposite directions. Participants are exploring the implications of this setup and its effects on the resulting magnetic field.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants are questioning whether the opposing magnetic fields would cancel each other out and what the implications of that would be. There are inquiries about the specifics of the coils, such as their dimensions and the nature of the magnetic fields generated. Some participants are considering the differences between short coils and long solenoids.

Discussion Status

The discussion is ongoing, with various participants providing insights and asking clarifying questions. There is an exploration of the vector nature of the magnetic fields and how they might interact based on their orientations. Some guidance has been offered regarding sketching the situation and considering the resultant magnetic fields.

Contextual Notes

Participants note the absence of specific dimensions for the coils and the lack of a figure to illustrate the problem. There is also mention of a lab context, which may impose additional constraints on the discussion.

mitchy16
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Homework Statement


Describe the magnetic field you would observe if two coils were connected with magnetic fields pointing in opposite directions.

Homework Equations


No equation

The Attempt at a Solution


If the magnetic field was pointing in opposite directions, would it mean that it would cancel out as a result of the opposing directions? I'm not sure if the question meant current, or if they are actually asking magnetic field. Thanks!
 
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mitchy16 said:

Homework Statement


Describe the magnetic field you would observe if two coils were connected with magnetic fields pointing in opposite directions.

Homework Equations


No equation

The Attempt at a Solution


If the magnetic field was pointing in opposite directions, would it mean that it would cancel out as a result of the opposing directions? I'm not sure if the question meant current, or if they are actually asking magnetic field. Thanks!
Are you familiar with that the external magnetic field looks like for a coil that is carrying a current?

BTW, is there a figure that goes with this question? You can upload the PDF or JPEG figure with the UPLOAD button in the lower right of the Reply window. The answer is a bit different for short coils versus long solenoid coils...
 
berkeman said:
Are you familiar with that the external magnetic field looks like for a coil that is carrying a current?

BTW, is there a figure that goes with this question? You can upload the PDF or JPEG figure with the UPLOAD button in the lower right of the Reply window. The answer is a bit different for short coils versus long solenoid coils...
As in the magnetic field wraps around the current carrying coil? Yes.
And no, sorry, there is no figure with this problem. It pertains to a lab, and in the lab the radius of the two coils was 10.5cm and they were approximately 15cm apart, if that helps any! Thank you!
 
mitchy16 said:
As in the magnetic field wraps around the current carrying coil? Yes.
And no, sorry, there is no figure with this problem. It pertains to a lab, and in the lab the radius of the two coils was 10.5cm and they were approximately 15cm apart, if that helps any! Thank you!
You left out a dimension... :smile:
 
mitchy16 said:

Homework Equations


No equation
Also, this is not quite right. What is the equation for the B-field generated by a coil (of a yet-to-be-specified length)?
 
berkeman said:
You left out a dimension... :smile:
The radius of loops is 10.5cm, distance between is 15cm, and distance to was 20cm?
I am not sure what else I'm missing, sorry I'm a bit confused!
berkeman said:
Also, this is not quite right. What is the equation for the B-field generated by a coil (of a yet-to-be-specified length)?
Would it be the following?
https://www.physicsforums.com/file:///C:/Users/rajinder/AppData/Local/Temp/msohtmlclip1/01/clip_image002.png
upload_2018-2-3_12-57-41-png.png

I have only been provided with this equation for the coils, I am not sure if there is a different one I should be using.
 

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mitchy16 said:
The radius of loops is 10.5cm, distance between is 15cm, and distance to was 20cm?
I am not sure what else I'm missing, sorry I'm a bit confused!
Sorry to be confusing, I was just fishing to see if you realized that the length of the coil was not being specified. If the coils are very short and compact, that is different from if they are long solenoids. I guess I'll assume they are short coils for this question?
mitchy16 said:
Would it be the following?
i'd have to check, but that looks reasonable. So if the coils are short, each one looks like the following, right? And when two short coils are close together, you just add the fields vectorially. So what are your answers to the questions now, based on the vector fields of short coils adding vectorially?

http://onetesla.com//media/wysiwyg/coil1_1_.gif
coil1_1_.gif
 

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  • #10
mitchy16 said:
Okay, so, just for clarification would they attract? Which would produce a larger magnetic field?
The original problem statement said the magnetic fields were pointing in opposite directions, so it's like having 2 bar magnets with the North poles facing toward the other bar magnet. Do they attract or repel? :smile:
mitchy16 said:

Homework Statement


Describe the magnetic field you would observe if two coils were connected with magnetic fields pointing in opposite directions.
So getting back to the original problem statement, sketch two short coils like that last figure I posted, and separate them by about 2 diameters on a common axis. Have the North poles (the pointy ends of the B-field vectors) face each other.

So since they are on the same axis, and the axial B-field goes straight out, you can imagine that the two B-fields will cancel on the coaxial axis right in the middle half-way between the two coils, right? But as you move along that middle axis between the coils one way or the other, the B-field will not be zero in general, right? Because the B-field of a short coil falls off with some power of the distance, the B-field will be strongest right in the middle of the source coil, and will fall off as you get farther away.

Can you start that sketch of the 2 coils spaced 2 diameters apart on the same axis? Start sketching the vector combination of the 2 B-fields that are shown in that last sketch I posted. Just add up the magnitude and directions of the B-field vectors at different locations, and ask yourself what the resultant direction and magnitude would be at each point due to the combinations of the two source coils.

Can you start that sketch and Upload it so we can check it? :smile:
 

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