ELECTRIC MOTOR

 ELECTRIC MOTOR

WORK EDUCTION

ELECTRIC MOTOR (DC MOTOR) An electric motor is a device for converting electric energy into mechanical energy. Thus, an electric motor is the revenue of an electric generator.There are two types of electric motors: AC motor and () DC motor. We shall here be described DC Motor

Principle. When a coil carrying current is placed in a magnetic field, it experiences a torque. As result of this torque, the coll begins to rotate.

Construction. It consists of the following five parts:

1. Armature. The armature consists of a large number of turns of insulated copper wire wound over a soft iron core

2 Field Magnet. The magnetic field (B) is supplied by a permanent magnet NS

3. Split-ring or Commutator. These are two halves of the same metallic ring. The ends of the armature coil are connected to these halves which also rotate with the armature.

4. Brushes or Sliding Contacts. These are two flexible metal plates or carbon rods B1, and B2, which are So fixed that they constantly touch the revolving rings.

S. Battery. The battery consists of a few cells and is connected across the brushes. The brushes pass the current to the ring from where it is carried to the armature

Working. Let us suppose that the battery sends current to the armature in the direction shown in Fig). Applying Fleming's Left Hand Rule (Motor Rule), we find that arm AD experiences a force which is acting outwards and perpendicular to it and arm BC experiences a force which is acting inwards and perpendicular to it. These two forces for a couple whose moment (ie, torque) makes the armature rotate in the anticlockwise direction.

(b) After the armature has completed half a revolution (ie, has turned through 180), the direction of current in the arms AD and BC is reversed. Now arm BC experiences an outward force and arm AD experiences an inward force,. The armature thus continues to rotate about its axis in the same, Le., anticlockwise The speed of rotation of the motor can be increased by

(i) increasing the strength of the current through the armature, (i) increasing the number of turns in the coil of the armature, (ii) increasing the area of the coil, and (iv) increasing the strength of the magnetic field.

Uses of DC Motors

1. These are used in electric fans (exhaust, ceiling or table)

2. These are used for pumping water.

3. Big DC motors are used for running tram-cars. 4. Small DC motors are used in various toys.