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what is dc generator?

An electric motor is a device which converts electrical energy into mechanical energy. In electric motor, electrical energy rotates a rod called shaft. Thus kinetic energy of the shaft and any device attached to it perform work.

Principle : It works on the principle of magnetic effect of current, that is, when a current carrying conductor is kept normally in a magnetic field, it experiences a force as a result of which the conductor begins to move. The direction of the force is determined by Fleming's left hand rule.

Construction : Figure shows the essential parts of d.c. Motor.

Armature : A rectangular coil ABCD of many turns of insulated copper wire wound on a soft iron core. The coil and its core as a whole is called as armature. The function of the coil is to increase strength of the magnetic field.

Field magnets : The armature rotates around a spindle between pole pieces N and S of a strong magnet. Axis of rotation is perpendicular to the magnetic field lines.

Commutator or split rings : A commutator is a copper ring split into two halves S1 and S2. The two ends of the coil A and D are soldered to the two halves S1 and S2. The two ends of the coil A and D are

soldered to the two halves S1 and S2 of a split ring commutator. The commutator rings are mounted on the shaft of the motor. They rotate when the coil rotates. The function of the commutator is to reverse the direction of current flowing through the coil from the battery.

Brushes : B1 and B2 are two flexible metal plates or carbon rods fixed to the base of the motor that press lightly against the two halves S1 and S2 of the commutator.

Battery : The battery is connected across the brushes which conveys current to the armature through the split rings.

Working : Let initially the plane of the coil is horizontal and the split ring S1 touches the brush B1 and the split ring S2 touches B2. The current flows in the coil in the direction ABCD. According to Fleming's left hand rule, a force F acts on the arm AB in the downward direction and a force F acts on the arm CD in the upward direction.

These two equal , unlike and parallel forces acting on the two sides of the coil constitute a couple and thereby rotate the coil in anticlockwise direction as shown in fig. (a). When the coil comes into the vertical position. i.e., normal to the plane of the paper with arm (DC up and AB down), the couple becomes zero. But due to inertia of motion, the coil passes through this position and split ring S1 comes in contact with B2 and S2 comes in contact with B1. Now the coil has rotated through 180o and the current flows through the coil in the direction DCBA. Now the arm DC experiences a downward force and arm BA experiences an outward force. Thus, the forces acting on the arms of the coil again form a couple due to which the coil starts rotating in an anticlockwise direction. Thus, the armature continues to rotate in anticlockwise direction.