Thursday, 8 December 2016



An led is a Light Emitting Diode.The American engineer Nick Holonyak is the inventor of LED on 1962.LED is a special type of diode that is specifically optimized to give off light.It consist of two different type of semi conductor device place side by side to each other,that are P and N type semi conductors.P type semi conductor contains positively charged holes and N type semi conductor contains negatively charged electrons.When current passed through semi conductor,the  negatively charged electrons and positive charged holes are forced to move to the PN junction.When a free electron come near a hole they combine each other and because the holes exist art a lower energy level than the free electrons.The electrons must lose energy to combine with the hole.This energy released in the form of photos of light.The amount of photon energy released determines the frequency/color of LED.

 Advantages of LED
  • They're tiny and relatively inexpensive.
  • They're easy to control electronically.
  • They last virtually forever. That makes them brilliant for traffic signals.
  • They make light electronically without getting hot and that means they save lots of energy.


    A machine that converts dc power into mechanical energy is known as dc motor. Its operation is based on the principle that when a current carrying conductor is placed in a magnetic field, the conductor experiences a mechanical force. The direction of the force is given by Fleming’s left hand rule.
      The main parts of a DC motor are:
  1. Stator magnet - A stator magnet may be a permanent magnet or an electromagnet that provides constant magnetic field 
  2. Armature - Armature is a rotating part.The armature is an electromagnet made by coiling thin wire around two or more poles of a metal core.The armature has an axle, and the commutator is attached to the axle.The electrical contacts to the rotating ring are called "brushes" since copper brush contacts were used in early motors. Modern motors normally use spring-loaded carbon contacts, but the historical name for the contacts has persisted.

Commutation in DC Motor
In order to produce unidirectional force(or torque) on the armature conductors of a motor, the conductors under any pole must carry the current in the same direction at all times.The function of commutator and brush gear in a dc motor is to cause the reversal of current in a conductor as it moves from one side of a brush to the other.



 The armature is connected to a DC power source through a pair of commutator rings. When the current flows through the coil an electromagnetic force is induced on it according to the Lorentz law, so the coil will start to rotate. You will notice that as the coil rotates, the commutator rings connect with the power source of opposite polarity. As a result, on the left side of the coil the electricity will always flow ‘away ‘and on the right side , electricity will always flow ‘towards ‘. This ensures that the torque action is also in the same direction throughout the motion, so the coil will continue rotating.