Introduction of DC Motor | Force on Current Carrying Conductor | Force exerted on the conductor | Concluslon

Introduction of DC Motor :

The DC machines are of two types namely DC generators and DC motors.
A DC generator converts mechanical energy into electricall energy. Whereas a DC motor converts the electrical energy into mechanical energy.
A prime mover supplies mechanical energy to the DC generator which generates electrical output energy. A motor accepts the energy in the electric form from D.C. source and converts it into mechanical energy at its output i (shaft).
In order to understand the operating principle of a dc motor, it is necessary to understand how does a current carrying conductor experience a force, when kept in a magnetic field.

Force on Current Carrying Conductor:

The concept that we are going to develop involves thei interaction of magnetic field and a current carrying conductori placed in it.
This concept is very important in understanding the basic principle of operation of a DC motor.
In this section we are going to learn about the forcei experienced by a current carrying conductor when placed in ai magnetic field.
The sequence of events is as follows : Development of individual fields. Interaction of the two individual magnetic fields. Force exerted on the conductor.

Let a straight conductor be placed in the magnetic field produced by a permanent magnet. Let the current flowing through the conductor be out of the plane of thei paper i.e. towards the user and let the magnetic field produced by the permanent magnet be as shown in Fig. 5.1.1.
The magnetic field produced by the conductor is also shown in Fig. 5.1.1. As the current is coming out, this field is in the anticlockwise direction. (as per the right hand thumb rule).
Interaction of the two magnetic fields: Due to presence of two magnetic fields simultaneously, an interaction between them will take place as shown in Fig. 5.1.2 (a).
The flux lines produced by the magnet and the conductor are in the opposite directions to each other at the top and hence cancel each other. Hence the number of flux lines at the top will reduce as shown in Fig. 5.1.2 (b).
At the bottom, the individual fields are in the same direction. hence will add or strengthen each other.i Therefore the number of flux lines at the bottom willi increase as shown in Fig. 5.1.2 (b).
The resultant pattern of the lines of force is shown in Fig. 5.1.2 (b).

Force exerted on the conductor:

We know the important propertes of the lines of force. One of the propertues states that the lines of force act as stretched elastc bands and always try to contract in length.
To do so the lines of foce at the bottom (additon of fields) will exert a force on the conductor in the upwardi direction as shown in Fig. 5.1.3
Hence a mechanical force is exerted on the conductor trom the high flux line area towards the low tlux line area (top) as shown in Fig, 5.1.3.

 Concluslon:

Thus if a current carrying conductor is placed in the magnetic field then it experiences a force as a result of the interaction between their individual magnetic fields. This will be the principle of operation of a DC motor.