If the key in the arrangement is taken out (the circuit is made open) and magnetic field lines are drawn over the horizontal plane ABCD, the lines are

  1. concentric circles
  2. elliptical in shape
  3. straight lines parallel to each other
  4. concentric circles near the point O but of elliptical shapes as we go away from it


If key is taken out then current will stop and no magnetic field exists due to the conductor. Therefore, at the point O, there will be earth’s magnetic field and they will be straight lines parallel to each other.

The correct option is C.

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