Class 12 Physics Electromagnetic Induction Varying Area in a moving rod

Methods of producing Induced Emf in a circuit: Varying Area (A) in a moving rod

  • Consider a rod which is moving inside the magnetic field.
  • When the loop enters the magnetic field; due to the magnetic fieldthe charges inside the rod experiences the magnetic force.
  • Because of this magnetic force the (+) ive and (-) ive charges separate out from each other, i.e. all the (+)ive charges get accumulated at one end and (-)ive charges on the other end.
  • Electrostatic potential is developed on the rod due to the accumulation of charges on both the ends of the rod when it enters the magnetic field.
  • Because of electrostatic potential an emf is induced.
  • This emf which was induced on the rod cannot be used for any practical purposes.
  • As it is an open circuit therefore induced emf on the rod cannot be used.
  • This induced emf is known as Motional Emf as it is generated because of motion of the rod inside the magnetic field.
  • Expression for motional emfe= Blengthv
  • Example: Flight.
    • At the tips of both the wings of the aeroplane emf is induced.
    • As it is not a closed loop so this emf cannot be used.



 Problem:- An aircraft with a wingspan of 40m flies with a speed of 1080km/hr in the eastward direction at a constant altitude in the northern hemisphere, where the vertical component of earth’s magnetic field is 1.75x10-5T.Find the Emf that develops between the tips of the wings?


V=1080km/hr= ((1080x1000)/60) = 300m/s


e=Blv=1.75x10-5 x40 x300


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