Summary of Unit 15: Electromagnetism

  • When electric current passes through a conductor, a magnetic field is set up in the space surrounding the conductor. In case of a straight current-carrying conductor, the lines of force are in the form of concentric circles.
  • Direction of magnetic field around a current-carrying conductor can be found using right hand rule: “Grasp a wire with your right hand such that your thumb is pointed in the direction of the conventional (positive) current. Then curling fingers of your hand will point in the direction of the magnetic field”.
  • When a straight current-carrying conductor is placed perpendicularly in a magnetic field, it experiences a force in a direction at right angles to both the directions of the field and the current.
  • When a current-carrying coil is placed in a magnetic field, it experiences a couple due to which the coil begins to rotate. A D.C motor operates on this principle. It converts electrical energy into mechanical energy.
  • The number of magnetic lines of force passing through a certain surface is known as the magnetic field strength through that surface.
  • When a magnetic through a coil is changing, an e.m.f. is field strength induced in it. The value of this induced e.m.f. is directly proportional to the rate of change of magnetic field strength.
  • An A.C generator consists of a coil and a magnet. When this coil is made to rotate in a magnetic field, the magnetic field strength through it continuously changes due to which an alternating voltage is induced in it. Thus, A.C generator converts mechanical energy into electrical energy.
  • If the change of current in a circuit induces a current in another circuit this phenomenon is known as mutual induction.
  • Transformer is an electrical device which is used to increase or decrease the value of an alternating voltage. It works on the principle of mutual induction.

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