question_answer

  Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of split ring in an electric motor? Or Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?

Answer:

  Electric MotorIt is a rotating device which convertselectrical energy into mechanical energy. Principle Electric motor works on the principle that when acurrent-carrying coil is placed in a magnetic field, two equal and opposite forces act upon it. When these two forces (whose lines of action are not same) act on a body, it tends to rotate.                                                                                                                                                                  (1) The diagram of electric motor is shown below (1) Working (i) Let coil ABCD be in horizontal position. When the key is switched on the current flows in the direction DCBA and then leaves through the brush Q, via ring R2. (ii) Applying Fleming's left hand rule, ? No force acts on arm CB and DA (as they are parallel to the magneticfield). ? Arm AB will experience a force inupward direction. ? Arm CD will experience an equal force in down ward direction. ? A torque, thus acts on the coiland it rotates in anti-clockwise direction. (iii) While rotating, when the coil reaches the vertical position, brushes P and Q lose contact with rings and thecurrent stops flowing. But the coil doesnot stop rotating due to inertia of motion. (iv) When the coil passes the vertical position, the ring automatically change their position and come in contact with opposite brushes. This reverses the direction of the current through the coil, but the direction of current on right hand side will be the same. So, the force on right hand side is always upward and force on left hand side of the coil is always in down ward direction, Hence, the coil continues to rotate in anti-clockwise direction.                                               (2) The split ring in an electric motor acts as commentator, it reverses the direction of current flowing through the armature coil (after every half rotation)                                                                                                               (1) Or Electric Generator or Dynamo It is a device which converts mechanical energy into electrical energy. Principle It works on the principle of the electromagnetic induction, i.e., when there isa relative change in magnetic field linked with a coil, there is an induced current in the coil.                                                                                                (1) Electric generators are of two types i.e., DC generators and AC generators (Alternators). The diagram of electric generator is shown below Working As the coil rotates, the two rings also rotate with the coil. The brushes B1 and B2 always keep contact with therotating ring. When the coil starts rotating with the arm AB moving up and CD moving down (clockwise) cutting the magneticlines then, according to Fleming's right hand rule, a current is induced in these arms in the direction ABCD. After a half rotation, arm CD moves up and AB moves down, hence the direction of current in each segment changes, giving rise to net induced current in the direction DCBA. Thus, after every rotation, polarity of the currentin the respective arm changes thereby generating an alternating current.                                              (2) The function of brushes (carbon-brushes) is to make contact with the rotating rings of the commentator.                                                                                                                                                                                                                            (1)