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Question: Answered & Verified by Expert
An infinite number of straight wires each carrying current I are equally placed as shown in the figure. Adjacent wires have current in the opposite direction. The net magnetic field at point P is

PhysicsMagnetic Effects of CurrentJEE Main
Options:
  • A μ0I4πln23ak^
  • B μ0I4πln43ak^
  • C μ0I4πln43a-k^
  • D Zero
Solution:
2206 Upvotes Verified Answer
The correct answer is: μ0I4πln43ak^
B1=μ04πIasinα+sinβ=μ04πI×2sin30acos30

  B = B = B 1 k ^ + B 2 k ^ + B 3 k ^ - B 4 k ^ + .....

     =μ04πI×2sin30acos30k^-μ04πI×2sin302acos30k^+μ04πI×2sin303acos30k^+.....

     =μ04π2I3ak^-μ04π2I3×2ak^+μ04π2I3×3ak^+.....

     =μ04π2I3a1-12+13-14+...k^=μ02I4π3aloge1+1k^=μ02I4π3aloge2k^

    =μ0I4π3aloge4k^

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