What are magnetic field lines? List three characteristics of these lines. Describe in brief an activity to study the magnetic field lines due to a current flowing in a circular coil.



Magnetic field lines are imaginary lines along which the north magnetic pole would move in a magnetic field.The tangent at any point on the magnetic field line gives the direction of the magnetic field at that point. 

Characteristics of magnetic field lines are:

  • Field lines arise from the North pole and end into the South pole of the magnet.  
  • Field lines are closed curves.  
  • Field lines are closer in stronger magnetic fields.  
  • Field lines never intersect each other as for two lines to intersect, there must be two directions of magnetic field  at a point, which is not possible.  
  • Direction of field lines inside a magnet is from South to North.  
  • The relative strength of the magnetic field is shown by the degree of closeness of field lines.   


Activity to study the magnetic field lines due to a current flowing in a circular coil:



  • A rectangular cardboard having holes is taken and a circular coil is passed through the holes . The coil is kept normal to the cardboard.  
  • The ends of the coil are connected to a battery through a  key. 
  • Iron filings are sprinkled uniformly on the cardboard . Key is plugged in. 
  • On tapping cardboard gently the iron filings get arranged in concentric circular loops around the holes on the cardboard indicating the magnetic field lines .
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CA Maninder Singh is a Chartered Accountant for the past 14 years and a teacher from the past 18 years. He teaches Science, Economics, Accounting and English at Teachoo