DIRECT CURRENT (D.C) MOTORS | ALTERNATING CURRENT (A.C) GENERATOR

D.C Motor

DIRECT CURRENT (D.C) MOTORS: As we can see bellow that the coil placed in a magnet cannot rotate more than 90 degree. The forces push the PQ side of the coil up and the RS side of the loop down until the loop reaches the vertical position. In this situation, plan of the loop is perpendicular to the magnetic field and the net force on the coil is zero. So the loop will not continue to turn because the forces are still up and down hence balanced.

working principle of direct current motor

How can we make this coil to rotate continuously. it can be done by reversing the direction of the current just as the coil reaches its vertical position. This reversal of current will allow to rotate the coil continuously. To the reverse direction of the current, the connection of the coil made through an arrangement of brushes and ring that is split into halves, called a Split Ring Commutator. Brushes, which are usually pieces of graphite, make contact with the commutator and allow current to flow in the loop. As the loop rotates, so does the commutator. The split ring is arranged so each half of the commutator change brushes just as the coil reaches the vertical position. Changing brushes revers the current in the loop.

As a result, the direction of the force on each side of the coil is reversed and it continue to rotate. This process repeat at each half-turn, causing coil to rotate in the magnetic field continuously. The result is an electric motor, which is a device that convert electric energy in rotational kinetic energy.

In a practical electrical motor, the coil called the armature, is made of many loops mounted on a shaft or axle. The magnetic field is produced either by permanent magnets or by elector magnates called a field coil. The torque on the armature and as a result the speed of the motor is controlled by the varying the current through the motor.

The total force acting on the armature can be increased by

• Increasing the number of turns of the coil.
• increasing the current in the coil.
• increasing the current in the magnetic field.
• increasing the area of the coil.

A.C Generator

 ALTERNATING CURRENT (A.C) GENERATOR: If a coil is rotated in a magnetic field, a current will be induced in the coil. The strength of induced current depend upon the number of magnetic lines of force passing through the coil. The number of the lines of magnetic force passing through the coil will be maximum when the plane of the coil is perpendicular to the liens of magnetic force. The numbers of the liens of magnetic force will be zero when plane of the coil is parallel to the line of force. Thus, a coil rotates in a magnetic field, the induced current in it continuously changes from maximum to minimum value and so on. This is a basic principle of which an A.C generator work.

The armature is to be arranged so that it can rotate freely in the magnetic field. As armature turns, the wire loop cut through the magnetic field liens and induced e.m.f. will be produced. The e.m.f. developed by the generator depends on the length of the wire rotating in the field. Increasing the number of loops in the armature, increases the wire length, there by increasing the induced e.m.f

Current from Generator 

When a generator is connected in a closed circuit, the induced e.m.f. generates an electric current. As the loop rotates the strength the and the direction of the current changes as shown in Fig Bellow.When the plane of will is perpendicular to field, the number of lines of magnetic force passing through it is maximum. But the change in the number of lines through the coil is minimum. So e.m.f. induced minimum.

The current is minimum when the plane of the loop is perpendicular to the magnetic field; that is, when the loop is in vertical position. As the loop rotates from the vertical to the horizontal position, it cuts through large magnetic field liens per unit of times, thus the e.m.f. and the current increase.

 When the loop is in the horizontal position, the plane of the loop becomes parallel to the field, so the e.m.f. and the current reaches its maximum value. As the loop continue to turn, the segment that was moving up begins to move down and reverse the direction of the e.m.f. and the current in the loop. This changes in a direction take place each time the loop turns through 80 degree. Thus, the e.m.f and the current changes smoothly from zero to some maximum value and back to zero value during each half turns of the loop.