Ampere's swimming rule about magnetic field around a current carrying conductor

[manjuvenamma]

We know that if current is flowing in the direction of z-axis (verical), magnetic field is formed in a plance perpendicular to that line i.e., in the XY plane. That is if you keep a compass in the XY plane it will experience a force as per the rule. But what will happen to a compass that is placed vertically i.e. along the z axis?

 

[rahuldandekar]

Depends on which plane it is free to rotate in. If it can align itself along the magnetic field in that plane, it will rotate and do so. If magnetic field lines are perpendicular to that plane, it cannot align itself with them, so it won't rotate.