0The principle, Construction and Working of a Motor
A motor is a device that converts Electrical energy to Mechanical energy.
Principle: It works on the principle of Motor effect, which states that when a current-carrying wire is placed in the presence of a magnetic field, it experiences a force.
Construction: An armature coil ABCD is placed between the two poles (N – S) of a magnet, thereby cutting its magnetic field lines. End A of the coil is connected to split ring C1 while end D is connected to split ring C2. The armature is mounted on a shaft attached to bearings and is free to perform rotational motion about its axis along with the split ring commutator. Carbon brushes B1 and B2 are connected to the positive and negative terminals of a cell, respectively. A switch is connected in series. As the commutator rotates, the split rings alternately come in contact with B1 and B2.
Working: Consider the position of the coil in Figure A when B1 is in contact with C1 and B2 with C2. The circuit is complete and current flows through the coil in the direction ABCD. Applying Fleming’s left-hand rule, the arm AB experiences a downward force while arm CD experiences an upward force. These two forces constitute a couple and rotate the coil in the anti-clockwise direction.
Consider what happens after 180° (half cycle) of rotation in Figure B. Brush B1 is now in contact with split ring C2 and B2 is in contact with C1. Hence the direction of current in the coil as a whole gets reversed (DCBA). Therefore, arm DC now experiences a downward force while arm AB experiences an upward force, thereby ensuring that the armature rotates continuously in the same (anti-clockwise direction).
Arms AD and BC do not experience any force as they are parallel to the magnetic field lines. During rotation, the brushes keep losing contact with the split rings momentarily, but this does not stop the motion due to rotational inertia.
The shaft transfers the rotational mechanical energy outside the motor where we can utilize it in many ways.
