Electric motor

04 Magnetic

THE ELECTRIC MOTOR

A motor is a device which converts electrical energy into mechanical energy. For example, a mixer has rotating blades that mash and mix things. The electric energy input to the mixer is converted into mechanical energy of rotation of the blades and thus the desired action is achieved.

PRINCIPLE OF AN ELECTRIC MOTOR
• A motor works on the principle that when a rectangular coil is placed in a magnetic field and current is passed through it, a force acts on the coil which rotates it continuously.
• Consider the poles of two bar magnets kept facing each other, with a small scape in between. A small length of conducting wire is made in the form of a loop and kept in the space between the magnets in such a way that it is in the magnetic field produced by the magnets. If the ends of the loop are connected to the battery terminals, the loop starts to rotate. This is because the magnetic field of the magnet interferes with the electric current flowing through the conductor. Due to the magnetic poles induced in the loop, the induced South Pole is attracted to the north pole and vice versa. When the direction of current in the loop reverses, the induced South Pole becomes North Pole and gets attracted to the south pole of the magnet. This causes the loop to rotate continuously.
PARTS OF AN ELECTRIC MOTOR
• A motor works on the principle that when a rectangular coil is placed in a magnetic field and current is passed through it, a force acts on the coil which rotates it continuously.
• Consider the poles of two bar magnets kept facing each other, with a small scape in between. A small length of conducting wire is made in the form of a loop and kept in the space between the magnets in such a way that it is in the magnetic field produced by the magnets. If the ends of the loop are connected to the battery terminals, the loop starts to rotate. This is because the magnetic field of the magnet interferes with the electric current flowing through the conductor. Due to the magnetic poles induced in the loop, the induced South Pole is attracted to the north pole and vice versa. When the direction of current in the loop reverses, the induced South Pole becomes North Pole and gets attracted to the south pole of the magnet. This causes the loop to rotate continuously.
CONSTRUCTION OF A ELECTRIC MOTOR
• An electric motor consists of a rectangular coil ABCD of insulated copper wire.
• The coil is placed between the two poles of a magnetic field such that the arm AB and CD are perpendicular to the direction of the magnetic field.
• Coil is mounted between the curved poles of a horseshoe-type permanent magnet M in such a way that it can rotate freely between the poles N and S on a shaft.
• A device which reverses the direction of current through a circuit is called commutator (or split ring).
• The two ends of the coil are soldered (or welded) permanently to the two half rings X and Y of a commutator.
• The function of carbon brushes is to make contact with the rotating rings of the commutator and through them to supply current to the coil.
WORKING OF A MOTOR:
• Current in the coil ABCD enters from the source battery through conducting brush X and flows back to the battery through brush Y.
• The coil and the axle O, mounted free to turn about an axis, rotate anti-clockwise.
• The force acting on arm AB pushes it downwards while the force acting on arm CD pushes it upwards.
• Thus the coil and the axle O, mounted free to turn about an axis, rotate anti-clockwise.
• At half rotation, Q makes contact with the brush X and P with brush Y.
• Therefore the current in the coil gets reversed and flows along the path DCBA.
• The reversal of current also reverses the direction of force acting on the two arms AB and CD. Thus the arm AB of the coil that was earlier pushed down is now pushed up and the arm CD previously pushed up is now pushed down. Therefore the coil and the axle rotate half a turn more in the same direction. The reversing of the current is repeated at each half rotation, giving rise to a continuous rotation of the coil and to the axle.

CONSTRUCTION OF COMMERCIAL MOTORS

In commercial motors:

(a) The coil is wound on a soft iron core. The soft iron core becomes magnetized and increases the strength of magnetic field. This makes the motor more powerful. The assembly of soft iron core and coil is called an armature.

(b) The coil contains a large number of turns of the insulated copper wire.

(c) A powerful electromagnet is used in place of permanent magnet.

USE OF AN ELECTRIC MOTOR

Electric motors are used in a variety of applications. Some of them are listed below

1. Drills
2. Water Pumps
3. Hard Disc Drives
4. Washing Machines
5. Industrial Equipment

The efficiency of a functioning motor is around as the remaining energy is dissipated as noise and heat.