The net magnetic field at the center

  • #1
PhysicsTest
201
23
Homework Statement:
Four, long, parallel power lines each carry 100-A currents. A cross-sectional diagram of these lines is a square, 20.0 cm on each side. For each of the three cases shown in , calculate the magnetic field at the center of the square.
Relevant Equations:
##B = \frac {\mu_0 I} {2a}##
The current direction is as follows
1601316385651.png

I think so much and do the right hand rule i get 0 at the center, but not sure why the answer is non zero. I have shown the directions of the magnetic fields, i have not shown the magnitudes of equal length but they all are equal. Why the answer is non zero, what mistake i am doing?

1601316443107.png
 

Answers and Replies

  • #2
BvU
Science Advisor
Homework Helper
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I see only one case ? Mixup of answers ?
 
  • #3
PhysicsTest
201
23
I see only one case ? Mixup of answers ?
The first two I could solve, this is the 3rd one which I am struggling to get answer.
 
  • #4
Gordianus
460
116
May I suggest drawing the arrows again?
 
  • #5
PhysicsTest
201
23
May I suggest drawing the arrows again?
I end up getting below the same,

1601320343395.png
 
  • #6
Gordianus
460
116
No, try again.
 
  • #7
PhysicsTest
201
23
No, try again.
Ok, chances are there of a below diagram
1601321196983.png

But a very tough one to know where it will be left. Am i correct here?
 
  • #8
Gordianus
460
116
Try drawing the B-lines of each wire
 
  • #9
PhysicsTest
201
23
Try drawing the B-lines of each wire
The B lines are like this
1601322227148.png

Everything seems to be left.
 
  • #10
Gordianus
460
116
Good! Now extend the lines to the center and draw the arrows again.
 
  • #11
PhysicsTest
201
23
1601324249923.png

Surely the tougher than i expected. Hope it is correct.
 
  • #12
Gordianus
460
116
Victory!
 
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  • #13
PhysicsTest
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Thank you very much for support.
 

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