Led

LED is an optical semiconductor device that converts electrical energy into light energy.  Also known as light emitting diode. And it also varies in different colors.
     

A semiconductor diode that emits light when current flow through it. When electrons in semiconductor recombine with electron wholes than an energy release in form of photon. Light emitting diodes emit either visible light or invisible infrared light when forward biased. The LEDs which emit invisible infrared light are used for remote controls.

 LEDs

A diagram of the inside of an LED is shown in Figure  The chip at the heart of the LED

consists of a p-n junction --- two different solid materials that have been joined together. It

is surrounded by a transparent, hard plastic that protects the LED from vibration and shock.

The LED is constructed in such a way that the light emitted by the chip is reflected off the

base it sits on and is focused through the top of the LED. Thus, the light is brightest at the top of LED.

p-n junctions

A solid can be a pure material in which all atoms are the same element. As a result, each

nucleus of the atom contained in this solid has the same electrical charge. Thus, each atom

in this solid has identical properties. The interactions among these atoms create the energy

bands and gaps that we have studied. Modern technology can create materials that are

very close to being all identical atoms. These pure materials have light emitting properties

much like we have studied here.

For today’s technology pure materials are not the most valuable. Instead, a wide range of

devices — from LEDs to computer chips — use almost pure materials into which an impu-

rity has been introduced. Then materials with different impurities are joined.

Suppose we start with a pure material and add atoms of a different element. These differ-

ent elements will have a different number of electrons than the atoms of the original mate-

rial. We place the impurities into two groups:

 • Donors, or n-type, have more electrons than the material’s pure elements.                                                They donate electrons to the solid.

 • Acceptors, or p-type, have fewer electrons than the material’s pure element. They

accept electrons from the solid.

Both the donors and acceptors have zero electrical charge. They have more or less charge

in the nucleus to balance the more or fewer electrons.

The LED chip consists of two solids – a material that has been supplied with donor atoms

and the same material that has been supplied with acceptor atoms. The combination is the called p-n junctions.

Layers of LED

A Light Emitting Diode (LED) consists of three layers: p-type semiconductor, n-type semiconductor and depletion layer. The p-type semiconductor and the n-type semiconductor are separated by a depletion region or depletion layer.

P-type semiconductor

When trivalent impurities are added to the intrinsic or pure semiconductor, a p-type semiconductor is formed.

In p-type semiconductor, holes are the majority charge carriers and free electrons are the minority charge carriers. Thus, holes carry most of the electric current in p-type semiconductor.

N-type semiconductor

When pentavalent impurities are added to the intrinsic semiconductor, an n-type semiconductor is formed.

In n-type semiconductor, free electrons are the majority charge carriers and holes are the minority charge carriers. Thus, free electrons carry most of the electric current in n-type semiconductor.

Depletion layer or region

Depletion region is a region present between the p-type and n-type semiconductor where no mobile charge carriers (free electrons and holes) are present. This region acts as barrier to the electric current. It opposes flow of electrons from n-type semiconductor and flow of holes from p-type semiconductor.

To overcome the barrier of depletion layer, we need to apply voltage which is greater than the barrier potential of depletion layer.

If the applied voltage is greater than the barrier potential of the depletion layer, the electric current starts flowing.

How Light Emitting Diode (LED) works?

Light Emitting Diode (LED) works only in forward bias condition. When Light Emitting Diode (LED) is forward biased, the free electrons from n-side and the holes from p-side are pushed towards the junction.

When free electrons reach the junction or depletion region, some of the free electrons recombine with the holes in the positive ions. We know that positive ions have less number of electrons than protons. Therefore, they are ready to accept electrons. Thus, free electrons recombine with holes in the depletion region. In the similar way, holes from p-side recombine with electrons in the depletion region.

Because of the recombination of free electrons and holes in the depletion region, the width of depletion region decreases. As a result, more charge carriers will cross the p-n junction.

Some of the charge carriers from p-side and n-side will cross the p-n junction before they recombine in the depletion region. For example, some free electrons from n-type semiconductor cross the p-n junction and recombines with holes in p-type semiconductor. In the similar way, holes from p-type semiconductor cross the p-n junction and recombines with free electrons in the n-type semiconductor.

Thus, recombination takes place in depletion region as well as in p-type and n-type semiconductor.

The free electrons in the conduction band releases energy in the form of light before they recombine with holes in the valence band.

In silicon and germanium diodes, most of the energy is released in the form of heat and emitted light is too small.

However, in materials like gallium arsenide and gallium phosphide the emitted photons have sufficient energy to produce intense visible light

Symbol of LED

capacitor

Capacitor is an electrical component in which we store Electrical energy electric field. A capacitor behavior like a battery for little bit time.

It's unit is FARAD, and it represented by F.

It consists of two parallel plates separated

by an insulating material called the dielectric

• In the neutral state, both plates have an equal 

number of free electrons

• When a voltage source is connected to the 

capacitor, electrons are removed from one plate and

an equal number are deposited on the other plate

• No electrons flow through the dielectric (insulator)

Capacitance of capacitor :

The capacitance of a capacitor -- how many farads it has -- depends on how it's constructed. More capacitance requires a larger capacitor. Plates with more overlapping surface area provide more capacitance, while more distance between the plates means less capacitance. The material of the dielectric even has an effect on how many farads a cap has. The total capacitance of a capacitor can be calculated with the equation:

Where ε_r is the dielectric's relative permittivity
(a constant value determined by the dielectric material), A is the amount of area the plates overlap each other, and d is the distance between the plates.

Charging & Discharging of a Capacitor

Consider the following circuit.

Assume that the capacitor is fully discharged and the switch connected to the capacitor has just been moved to position A. The voltage across the 100uf capacitor is zero at this point and a charging current ( i ) begins to flow charging up the capacitor until the voltage across the plates is equal to the 12v supply voltage. The charging current stops flowing and the capacitor is said to be “fully-charged”. Then, Vc = Vs = 12v.

Once the capacitor is “fully-charged” in theory it will maintain its state of voltage charge even when the supply voltage has been disconnected as they act as a sort of temporary storage device. However, while this may be true of an “ideal” capacitor, a real capacitor will slowly discharge itself over a long period of time due to the internal leakage currents flowing through the dielectric.

This is an important point to remember as large value capacitors connected across high voltage supplies can still maintain a significant amount of charge even when the supply voltage is switched “OFF”.

If the switch was disconnected at this point, the capacitor would maintain its charge indefinitely, but due to internal leakage currents flowing across its dielectric the capacitor would very slowly begin to discharge itself as the electrons passed through the dielectric. The time taken for the capacitor to discharge down to 37% of its supply voltage is known as its Time Constant.

If the switch is now moved from position A to position B, the fully charged capacitor would start to discharge through the lamp now connected across it, illuminating the lamp until the capacitor was fully discharged as the element of the lamp has a resistive value.

The brightness of the lamp and the duration of illumination would ultimately depend upon the capacitance value of the capacitor and the resistance of the lamp (t = R*C). The larger the value of the capacitor the brighter and longer will be the illumination of the lamp as it could store more charge.

Energy stored by capacitor:

When a capacitor charging energy transferred from source voltage to capacitor.

When the capacitor is removed energy from source the potential deference across it's plate remain constant.

Since no current is  required to maintain this potential deference. The capacitance store electron electric energy. This energy stores in electric fieldBetween the plates.

The energy stored by a fully charged capacitor.

Where is

                   W  =   symbol of energy

                   J    = Unit if energy

Capacitor in series:

When capacitors are connected in series, the total capacitance is less than any one of the series capacitors’ individual capacitances. If two or more capacitors are connected in series, the overall effect is that of a single (equivalent) capacitor having the sum total of the plate spacings of the individual capacitors. As we’ve just seen, an increase in plate spacing, with all other factors unchanged, results in decreased capacitance.

Thus, the total capacitance is less than any one of the individual capacitors’ capacitances. The formula for calculating the series total capacitance is the same form as for calculating parallel resistances:

capacitor in parallel

When capacitors are connected in parallel, the total capacitance is the sum of the individual capacitors’ capacitances. If two or more capacitors are connected in parallel, the overall effect is that of a single equivalent capacitor having the sum total of the plate areas of the individual capacitors. As we’ve just seen, an increase in plate area, with all other factors unchanged, results in increased capacitance.

Thus, the total capacitance is more than any one of the individual capacitors’ capacitances. The formula for calculating the parallel total capacitance is the same form as for calculating series resistances:

           

As you will no doubt notice, this is exactly the opposite of the phenomenon exhibited by resistors. With resistors, series connections result in additive values while parallel connections result in diminished values. With capacitors, its the reverse: parallel connections result in additive values while series connections result in diminished values.

   

Ammeter

It's Electronic device in which we measure current in amperes (A)in close Circuit. It is connected in series with circuit.

The effective resistance of ammeter is low

The Resistance of an ammeter is zero. A moving coil of galvanometer is converted in to an ammeter by connected a suitable low resistance in parallel to it. Circuit must be disconnected in order to attach

the ammeter. Ammeter considered as less accurate value.

Type of ammeter

There are 7 type of ammeter.

1.Moving coil 

2-Moving magnet

 3-Electrodynamic

 4-Moving iron 

5-Hot wire

 6-Digital 

7-Integrating

Moving coil ammeter:

                                  The D'Arsonval galvanometer is a moving coil ammeter. It uses magnetic deflection, where current passing through a coil causes the coil to move in a magnetic field. The modern form of this instrument was developed by Edward Weston, and uses two spiral springs to provide the restoring force. The uniform air gap between the iron core and the permanent magnet poles make the deflection of the meter linearly proportional to current. These meters have linear scales. Basic meter movements can have full-scale deflection for currents from about 25 microamperes to 10 milliamperes. Because the magnetic field is polarised, the meter needle acts in opposite directions for each direction of current. A DC ammeter is thus sensitive to which way round it is connected; most are marked with a positive terminal, but some have centre-zero mechanisms and can display currents in either direction. A moving coil meter indicates the average (mean) of a varying current through it, which is zero for AC. For this reason moving-coil meters are only usable directly for DC, not AC.This type of meter movement is extremely common for both ammeters and other meters derived from them, such as voltmeters and ohmmeters. Although their use has become less common in recent decades, this type of basic movement was once the standard indicator mechanism for any analogue displays involving electrical machinery. Moving Coil Instruments are used for measuring DC quantities. They can be used on AC systems when fed through bridge rectifiers, but some products are rectified moving coil and can be used in ac systems directly.

Energy meter

Single phase Energy meter   

Single phase induction type energy meter is also popularly known as watt-hour meter. This name is given to it. This article is only focused about its constructional features and its working. Induction type energy meter essentially consists of following components:  

1. Driving system 

2. Moving system 

3. Braking system and 

4. Registering system  

Driving system

                           It consists of two electromagnets, called “shunt” magnet and “series” magnet, of laminated construction. A coil having large number of turns of fine wire is wound on the middle limb of the shunt magnet.

  This coil is known as “pressure or voltage” coil and is connected across the supply mains. This voltage coil has many turns and is arranged to be as highly inductive as possible. In other words, the voltage coil produces a high ratio of inductance to resistance. This causes the current and therefore the flux, to lag the supply voltage by nearly 90 degree 

 Adjustable copper shading rings are provided on the central limb of the shunt magnet to make the phase angle displacement between magnetic field set up by shunt magnet and supply voltage is approximately 90 degree.  

The copper shading bands are also called the power factor compensator or compensating loop. The series electromagnet is energized by a coil, known as “current” coil which is connected in series with the load so that it carry the load current. The flux produced by this magnet is proportional to, and in phase with the load current. 

Moving system :

                               The moving system essentially consists of a light rotating aluminium disk mounted on a vertical spindle or shaft. The shaft that supports the aluminium disk is connected by a gear arrangement to the clock mechanism on the front of the meter to provide information that consumed energy by the load. The time varying (sinusoidal) fluxes produced by shunt and series magnet induce eddy currents in the aluminium disc The interaction between these two magnetic fields and eddy currents set up a driving torque in the disc. The number of rotations of the disk is therefore proportional to the energy consumed by the load in a certain time interval and is commonly measured in kilowatt-hours (Kwh). 

Braking system :

                            Damping of the disk is provided by a small permanent magnet, located diametrically opposite to the a.c magnets. The disk passes between the magnet gaps. The movement of rotating disc through the magnetic field crossing the air gap sets up eddy currents in the disc that reacts with the magnetic field and exerts a braking torque. By changing the position of the brake magnet or diverting some of the flux there form, the speed of the rotating disc can be controlled. 

Registering Or counting system

The registering or counting system essentially consists of gear train, driven either by worm or pinion gear on the disc shaft, which turns pointers that indicate on dials the number of times the disc has turned.  The energy meter thus determines and adds together or integrates all the instantaneous power values so that total energy used over a period is thus known. Therefore, this type of meter is also called an “integrating” meter. 

DC circuit

  DC  Circuits:

  Prerequisites:

                                   A  DC  circuit  (Direct  Current  circuit)  is  an  electrical  circuit  that  consists  of  any     combination  of  constant  voltage  sources,  constant  current  sources,  and  resistors.  In  this  case, the  circuit  voltages  and  currents  are  constant,  i.e.,  independent  of  time.  More  technically, a  DC  circuit  has  no  memory.  That  is,  a  particular  circuit  voltage  or  current  does  not  depend on  the  past  value  of  any  circuit  voltage  or  current.  This  implies  that  the  system  of  equations that  represent  a  DC  circuit  do not involve  integrals  or  derivatives. 

Introduction:

                    In  electronics,  it  is  common  to  refer  to  a  circuit  that  is  powered  by  a  DC  voltage  source  such as  a  battery  or  the  output  of  a  DC  power  supply  as  a  DC  circuit  even  though  what  is  meant  is that the  circuit  is DC  powered. If  a  capacitor  and/or  inductor  is  added  to  a  DC  circuit,  the  resulting  circuit  is  not, strictly  speaking,  a  DC  circuit.  However,  most  such  circuits  have  a  DC  solution.  This  solution gives  the  circuit  voltages  and  currents  when  the  circuit  is  in  DC  steady  state.  More technically,  such  a  circuit  is  represented  by  a  system  of  differential  equations.  The solution  to  these  equations  usually  contains  a  time  varying  or  transient  part  as  well  as constant  or  steady  state  part.  It  is  this  steady  state  part  that  is  the  DC  solution.  There  are  some circuits  that  do  not  have  a  DC  solution.  Two  simple  examples  are  a  constant  current source  connected  to  a  capacitor  and  a  constant  voltage  source  connected  to  an  inductor. 

Electro-magnetic  force(E.M.F): 

                                                   Electromotive  Force  is,  the  voltage  produced  by  an  electric  battery  or  generator  in an  electrical  circuit  or,  more  precisely,  the  energy  supplied  by  a  source  of  electric  power in  driving  a  unit  charge  around  the  circuit.  The  unit  is  the  volt.  A  difference  in  charge between  two  points  in  a  material  can  be  created  by  an  external  energy  source  such  as  a battery.  This  causes  electrons  to  move  so  that  there  is  an  excess  of  electrons  at  one  point  and a  deficiency  of  electrons  at  a  second  point.  This  difference  in  charge  is  stored  as  electrical potential  energy  known  as  emf.  It  is the  emf  that  causes  a  current  to flow  through  a  circuit. 

Voltage: 

              Voltage  is  electric  potential  energy  per  unit  charge,  measured  in  joules  per coulomb.  It  is  often  referred  to  as  "electric  potential",  which  then  must  be  distinguished  from electric  potential  energy  by  noting  that  the  "potential"  is  a  "per-unit-charge"  quantity.  Like mechanical  potential  energy,  the  zero  of  potential  can  be  chosen  at  any  point,  so  the  difference in  voltage  is  the  quantity  which  is  physically  meaningful.  The  difference  in  voltage  measured when  moving  from  point  A  to  point  B  is  equal  to  the  work  which  would  have  to  be  done,  per unit  charge,  against  the  electric  field  to move  the  charge  from  A  to  B. 

Potential  Difference:

                                       A  quantity  related  to  the  amount  of  energy  needed  to  move  an  object  from  one  place  to another  against  various  types  of  forces.  The  term  is  most  often  used  as  an  abbreviation  of "electrical  potential  difference",  but  it  also  occurs  in  many  other  branches  of  physics.  Only changes  in potential or  potential energy  (not  the  absolute  values)  can  be  measured. 

Electrical  potential  difference  is  the  voltage  between  two  points,  or  the  voltage  drop transversely  over  an  impedance  (from  one  extremity  to  another).  It  is  related  to  the  energy needed  to  move  a  unit  of  electrical  charge  from  one  point  to  the  other  against  the  electrostatic field  that  is  present.  The  unit  of  electrical  potential  difference  is  the  volt  (joule  per  coulomb). Gravitational  potential  difference  between  two  points  on  Earth  is  related  to  the  energy  needed  to move  a  unit  mass  from  one  point  to  the  other  against  the  Earth's  gravitational  field.  The  unit of  gravitational  potential  differences  is  joules  per  kilogram. 

Electromagnetism: 

                               When  current  passes  through  a  conductor,  magnetic  field  will  be  generated  around  the conductor  and  the  conductor  become  a  magnet.  This  phenomenon  is  called  electromagnetism. Since  the  magnet  is  produced  electric  current,  it  is  called  the  electromagnet.  An  electromagnet  is a  type  of  magnet  in  which  the  magnetic  field  is  produced  by  a  flow  of  electric  current.  The magnetic  field  disappears  when  the  current  ceases.  In  short,  when  current  flow  through  a conductor,  magnetic  field  will  be  generated.  When  the  current  ceases,  the  magnetic  field disappear. 

Applications  of  Electromagnetism: 

                                                    Electromagnetism  has  numerous  applications  in  today's  world  of  science  and  physics.  The very  basic  application  of  electromagnetism  is  in  the  use  of  motors.  The  motor  has  a  switch  that continuously  switches  the  polarity  of  the  outside  of  motor.  An  electromagnet  does  the  same thing.  We  can  change  the  direction  by  simply  reversing  the  current.  The  inside  of  the  motor has  an  electromagnet,  but  the  current  is  controlled  in  such  a  way  that  the  outside  magnet repels  it. 

Another  very  useful  application  of  electromagnetism  is  the  "CAT  scan  machine."  This machine  is  usually  used  in  hospitals  to  diagnose  a  disease.  As  we  know  that  current  is present  in  our  body  and  the  stronger  the  current,  the  strong  is  the  magnetic  field.  This scanning  technology  is  able  to  pick  up  the  magnetic  fields,  and  it  can  be  easily  identified where  there  is a  great  amount  of  electrical  activity  inside  the  body .

The  work  of  the  human  brain  is  based  on  electromagnetism.  Electrical  impulses  cause the  operations  inside  the  brain  and  it  has  some  magnetic  field.  When  two  magnetic  fields  cross each  other  inside  the  brain,  interference  occurs which is not healthy  for the  brain.

 Ohm’s  Law: 

                          Ohm's  law  states  that  the  current  through  a  conductor  between  two  points  is  directly proportional  to  the  potential  difference  or  voltage  across  the  two  points,  and  inversely proportional  to  the  resistance  between  them.  

The  mathematical  equation  that  describes  this relationship  is:

                      I=V/R
  

 where  I  is  the  current  through  the  resistance  in  units  of  amperes,   V is  the  potential  difference  measured  across  the  resistance  in  units  of  volts,   and  R  is  the  resistance  of  the  conductor  in  units  of  ohms.   More  specifically,  Ohm's  law  states  that  the  R  in  this  relation  is  constant, independent  of  the  current. 

Voltage

Voltage : -

         
                 Voltage  is  electric  potential  energy  per  unit  charge,  measured  in  joules  per coulomb.  It  is  often  referred  to  as  "electric  potential",  which  then  must  be  distinguished  from electric  potential  energy  by  noting  that  the  "potential"  is  a  "per-unit-charge"  quantity.  Like mechanical  potential  energy,  the  zero  of  potential  can  be  chosen  at  any  point,  so  the  difference in  voltage  is  the  quantity  which  is  physically  meaningful.  The  difference  in  voltage  measured when  moving  from  point  A  to  point  B  is  equal  to  the  work  which  would  have  to  be  done,  per unit  charge,  against  the  electric  field  to move  the  charge  from  A  to  B. 

Electric  Potential:

                             The  electric  potential  at  any  point  in  an  electric  field  is  defined  as  the  work  done  in  brining  an unit  positive  charge  (Q) from infinity  to that point against  the electric  field .

                             V= IR

Where is

       V = voltage

       I  = current

       R = resistance

 It dimension , 

                    Dimension: M L² T⁻³ I⁻¹

The unit of potential difference is Volt (V) which is also equal to Joule per Coulomb (J/C). The SI unit for voltageis Volt and is represented by the letter v. volt is a derived SI unit of electromotive force or electric potential.

Potential  Difference: 

                       
                  A  quantity  related  to  the  amount  of  energy  needed  to  move  an  object  from  one  place  to another  against  various  types  of  forces.  The  term  is  most  often  used  as  an  abbreviation  of "electrical  potential  difference",  but  it  also  occurs  in  many  other  branches  of  physics.  Only changes  in potential or  potential energy  (not  the  absolute  values)  can  be  measured. Electrical  potential  difference  is  the  voltage  between  two  points,  or  the  voltage  drop transversely  over  an  impedance  (from  one  extremity  to  another).  It  is  related  to  the  energy needed  to  move  a  unit  of  electrical  charge  from  one  point  to  the  other  against  the  electrostatic field  that  is  present.  The  unit  of  electrical  potential  difference  is  the  volt  (joule  per  coulomb). Gravitational  potential  difference  between  two  points  on  Earth  is  related  to  the  energy  needed  to move  a  unit  mass  from  one  point  to  the  other  against  the  Earth's  gravitational  field.  The  unit of  gravitational  potential  differences  is  joules  per  kilogram.

Electro-magnetic  force(E.M.F): 

                                           Electromotive  Force  is,  the  voltage  produced  by  an  electric  battery  or  generator  in an  electrical  circuit  or,  more  precisely,  the  energy  supplied  by  a  source  of  electric  power in  driving  a  unit  charge  around  the  circuit.  The  unit  is  the  volt.  A  difference  in  charge between  two  points  in  a  material  can  be  created  by  an  external  energy  source  such  as  a battery.  This  causes  electrons  to  move  so  that  there  is  an  excess  of  electrons  at  one  point  and a  deficiency  of  electrons  at  a  second  point.  This  difference  in  charge  is  stored  as  electrical potential  energy  known  as  emf.  It  is the  emf  that  causes  a  current  to flow  through  a  circuit. 

Resistance

Resistors  are one of the basic building blocks of electrical circuits.  Resistance occurs in  all materials, but resistors  are discrete components manufactured  to create an exact amount of intended resistance in a circuit.   Resistors are made of a mixture  of clay and carbon, so they are part conductor part insulator.   Because of this, they conduct electricity, but only with a set amount of resistance added.   The value of the resistance is carefully controlled.  Most resistors have four  color bands. The first band reveals the first digit of the value.  The second band reveals the second digit of the value.  The third band is used to multiply the value digits.  The fourth band  tells the tolerance of  the accuracy of the total value.  If no fourth band is present, it is assumed that the tolerance is plus or minus 20%. 

Resistance color code

Here are the digits represented by  the colored bands found on a resistor: 

Ohm’s law states this mathematical formula: Voltage is equal to resistance multiplied by the current flow, or  

                 E=IR. 

As with any algebraic formula, it is possible to rearrange the terms in order to solve the equation for a  specific unit of measurement. Two  algebraic equivalents of the formula would be:

                  

                 I=E/R   

                 R=E/I 

A very handy  magic triangle  is available that makes it easy to remember  the different permutations of  this formula.   

      

               E =IR

Cover the value to be determined with your finger,  and the relationship of  the other two are already in the proper form.   (Example: you need to know the amount of current flowing in  a circuit with 100Ω of resistance and 100 volts of pressure.   Cover I, the  symbol for current, and the remaining two symbols, E and R, appear in their correct relationship E/R.) 

         It's unit is ohm (Ω).

  

Resistance in series: 

                   A series of something  generally means connected along a line,  or  in  a row, or  in an order of some sort.  In electronics,  series resistance means that the resistors are connected one after the  other,  and that there is only  one path for current to flow through. 

Here is an example of  resistance in series: 

            R(T) = R¹+ R²+R³.   OHM'S

LAW OF SERIES CIRCUIT

1) Individual resistances add  up to  the total circuit resistance. 

2) Current through the circuit is the same at every point. 

3) Individual  voltages throughout  the circuit add up  to the total voltage. 

Resistance in parallel:

                         

There is another way to place more than one resistance into a circuit rather than in series.  Here  is a standard type of parallel circuit. 

            

In this example, each resistor has its own discrete path  to the voltage source, and if one of the pathways is opened, the other will still operate.  In a parallel circuit, the voltage in  each part of  the circuit remains constant, but the current varies in accordance with where a  reading is taken. This is the opposite of the way a series circuit operates.  

 There are many different ways to organize a parallel circuit.  In the  practical world, most wiring  is done in  parallel so that  the voltage to any one part of the network is the same as the voltage  supplied to  any other part of  it.   Having a  constant voltage is very important because electrical devices are designed to operate from a specific pressure.  It  would be  impractical to change that voltage at will throughout the electrical service. 

Although  the wiring  running between the lights is arranged differently, these  lamps have the same electrical connection as the lamps depicted in the previous schematic drawing.  No  matter how convoluted the wiring in a  lighting system may be, all of the circuits involved are  still in parallel, and all of the outlets have the same 120v service.

 LAWS OF PARALLEL CIRCUITS :

1) The reciprocals of all the  individual resistances add up to the reciprocal of the total circuit resistance.

            1/RT  = 1/R1  + 1/R2  + 1/R3  … 

2) Voltage  through  the  circuit  is the  same at every point.

 3)  Individual current  draws throughout the circuit add up to the total current  draw.  

                  IT  =.  I1 + I2  + I3......

current

The Current is flow of Electric charge Carrier in which we can harness to do work. 

Current is the rate at which charge is flowing.

Electric charge also known as electron.

There is two type of current :

1. DC current. (Direct current)

2. AC current. ( Alternating current)

1. Direct current

                      In Dc Current flow of Electric charge in one direction. It is steady state of constant voltage circuit.

2. Alternating current

                        In Alternating current (AC) is the flow of electric charge that periodically reverses direction.

   

Diode

                           Diode
Diode is a two-terminal electronic component that conducts current primarily in one direction. it has low (ideally zero) resistance in one direction, and high (ideally infinite) Resistance in the other. A diode vacuum tube or thermionic diode is a vacuum tube with two electrodes, a heated cathode and a plate, in which electrons can flow in only one direction, from cathode to plate. A semiconductor diode, the most commonly used type today, is a crystalline piece of semiconductor material with a p–n junction connected to two electrical terminals.Semiconductor diodes were the first semiconductor electronic devices. The discovery of asymmetric electrical conduction across the contact between a crystalline mineral and a metal was made by German physicist Ferdinand Braun in 1874. Today, most diodes are made of silicon, but other materials such as gallium arsenide and germanium are also used.

 Main function: 

               The most common function of a diode is to allow an electric current to pass in one direction (called the diode's forwarddirection), while blocking it in the opposite direction (the reversedirection). As such, the diode can be viewed as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current (ac) to direct current (dc). Forms of rectifiers, diodes can be used for such tasks as extracting modulation from radio signals in radio receivers.

                         semiconductor diode. A diode made of semiconductorcomponents, usually silicon. The cathode, which is negatively charged and has an excess of electrons, is placed adjacent to the anode, which has an inherently positive charge, carrying an excess of holes.

  

     Use of semiconductor :

         Diodes regulate the flow of voltage in a circuit

The simplest semiconductor component—the diode—performs a variety of useful functions related to its core purpose of managing the direction of the flow of electrical current. Diodes allow current to flow through them in one direction only.

Semiconductor Diode – Internal construction

Semiconductor diode consists of two, differently doped semiconductor crystals – “p” and “n” types. Together, they form so-called “p-n junction”, where the “n” layer(with electron donor dopants) has an excess amount of electrons, which are the majority carriers there (we have more electrons (-) than electron holes (+)). However, in the “p” layer (electron acceptor dopants) the majority carriers are electron holes (+) rather than electrons (-), so we have more holes “to fill”, than electrons available. The electron hole is a vacancy created by the electron “travelling” from its initial place to some other location in that crystal. In reality, there is no such thing as “a hole”, but that lack of electron kind of makes it a positively charged particle, which attracts negative electrons to form a pair again (holes can move too).
After they combine, a proportional distribution of electrons begins. Electrons, which previously lacked in “p” layer are transferred there from “n” layer, where were too many of them. So, “n” layer is a good friend for “p” layer, right? 🙂 And this is where so-called depletion region is formed, which prevents the flow of the electric current (thermodynamic equilibrium).

.

 2. P-N junction in state of thermodynamic equilibrium
To allow the flow of the electric current through the “p-n junction” (electric valve on), external positive electric voltage must be applied to “push” and help large group of electrons and holes to meet together (forward bias of the diode). After they are “pushed” through the depletion region with enough force (V_F = 0,7V) diode starts conducting current, so it starts to flow through it.

. 3. P-N junction forward-biased (electric valve on)

To make sure, that the electric current won’t flow (electric valve off), it is needed to apply external negative voltage to the semiconductor diode (reverse bias) to make depletion region even larger (illustration below).

Fig. 4. P-N junction reverse-biased (electric valve off)

With passing time, technological requirements were increasing what resulted in development of new types of diodes. When a semiconductor is combined with the corresponding metal, we acquire MS junction (Metal-Semiconductor), which also possesses rectifyingproperties (current conduction in one direction) – it is used for example in fast Schottky diodes.

Types of Semiconductor Diodes

• Rectifier diode – alternating current rectification,
• Zener diode – stabilization of voltage and current in electronic systems,
• Light Emitting Diode (LED) – emits light in the infrared or visible light spectrum,
• Variable capacitance diode – its capacity depends on the voltage applied to it in the reverse bias,
• Switching diode – used in pulse electronic systems that require very fast switching times,
• Tunnel diode – specially designed diode characterized by the negative dynamic resistance region,
• Photodiode – diode that works as photodetector – it reacts to light radiation (visible, infrared or ultraviolet),
• Gunn Diode – component used in high-frequency electronics.

ac instantaneous and rms value

AC Instantaneous  and  RMS Value:

 Instantaneous  Value: 

                 The  Instantaneous  value  of  an  alternating  voltage  or  current  is  the  value  of  voltage  or current  at  one  particular  instant.  The  value  may  be  zero  if  the  particular  instant  is  the  time  in  the cycle  at  which  the  polarity  of  the  voltage  is  changing.  It  may  also  be  the  same  as  the  peak  value, if  the  selected  instant  is  the  time  in  the  cycle  at  which  the  voltage  or  current  stops  increasing  and starts  decreasing.  There  are  actually  an  infinite  number  of  instantaneous  values  between  zero  and the  peak  value. 

RMS Value: 

               The  average  value  of  an  AC  waveform  is  NOT  the  same  value  as  that  for  a  DC  waveforms average  value.  This  is  because  the  AC  waveform  is  constantly  changing  with  time  and  the heating  effect  given  by  the  formula  (  P  =  I  2.R  ),  will  also  be  changing  producing  a  positive power  consumption.  The  equivalent  average  value  for  an  alternating  current  system  that  provides the  same  power  to  the  load  as  a  DC  equivalent  circuit  is  called  the  "effective  value".  This effective  power  in  an  alternating  current  system is  therefore  equal to: (  I2.R.  Average). As  power  is  proportional  to  current  squared,  the  effective  current,  I  will  be  equal  to  √  I  2  Ave. Therefore,  the  effective  current  in  an  AC  system is  called  the Root  Mean  Squared  or  R.M.S. 

                 

AC CIRCUIT

AC Circuits :. 
                            Prerequisites:
  An  alternating  current  (AC)  is  an  electrical  current,  where  the  magnitude  of  the current  varies  in  a  cyclical  form,  as  opposed  to  direct  current,  where  the  polarity  of  the  current stays  constant.


The usual  waveform  of  an  AC  circuit  is  generally  that  of  a  sine  wave,  as  this  results  in the  most  efficient  transmission  of  energy.  However  in  certain  applications  different  waveforms are  used,  such  as  triangular  or  square  waves.


Introduction :
 Used  generically,  AC  refers  to  the  form  in  which  electricity  is  delivered  to  businesses and  residences.  However,  audio  and  radio  signals  carried  on  electrical  wire  are  also  examples of  alternating  current.  In  these  applications,  an  important  goal  is  often  the  recovery  of information  encoded  (or  modulated)  onto the  AC  signal.

 Kirchhoff’s  law: Kirchhoff's  Current  Law: First  law  (Current  law  or  Point  law): Statement: The  sum  of  the  currents  flowing  towards  any  junction  in  an  electric  circuit  equal  to  the  sum  of currents flowing  away  from  the junction. 


 Kirchhoff's  Current  law  can  be  stated  in  words  as  the  sum  of  all  currents flowing  into  a  node  is  zero.  Or  conversely,  the  sum  of  all  currents  leaving  a  node  must be  zero.  As  the  image  below  demonstrates,  the  sum  of  currents  Ib,  Ic,  and  Id,  must equal  the  total  current  in  Ia.  Current  flows  through  wires  much  like  water  flows through  pipes.  If  you  have  a  definite  amount  of  water  entering  a  closed  pipe  system, the  amount  of  water  that  enters  the  system  must  equal  the  amount  of  water  that exists  the  system.  The  number  of  branching  pipes  does  not  change  the  net  volume  of water  (or  current  in our  case)  in  the  system.
   

Kirchhoff's  Voltage  Law: Second  law  (voltage  law  or  Mesh  law):  

Statement:

 In  any  closed  circuit  or  mesh,  the  algebraic  sum  of  all  the  electromotive  forces  and  the voltage  drops  is  equal  to  zero.  

 Kirchhoff's  voltage  law  can  be  stated  in  words  as  the  sum  of  all  voltage  drops  and  rises  in a  closed  loop  equals  zero.  As  the  image  below  demonstrates,  loop  1  and  loop  2  are  both  closed loops  within  the  circuit.  The  sum  of  all  voltage  drops  and  rises  around  loop  1  equals  zero,  and the  sum  of  all  voltage  drops  and  rises  in  loop  2  must  also  equal  zero.  A  closed  loop  can  be defined  as  any  path  in  which  the  originating  point  in  the  loop  is  also  the  ending  point  for  the loop.  No  matter  how  the  loop  is  defined  or  drawn,  the  sum  of  the  voltages  in  the  loop  must  be zero .

   The sum of all the voltages around a loop is equal to zero.                                V1 + v₂ + v₃ +v₄ = 0

Steady State  Solution of DC Circuits: Resistance  in  series  connection:

The resistors  R1,  R2,  R3  are  connected  in  series  across  the  supply  voltage  “V”.  The  total  current flowing  through  the  circuit  is  denoted  as  “I”.  The  voltage  across  the  resistor  R1, R2  and  R3  is  V1, V2, and V3  respectively. 

  V1  =  I*R1  (as per ohms law) 

V2.   =  I*R2

 V3   =  I*R3

 V     =  V1+V2+V3 

         =  IR1+IR2+IR3 

          =  (R1+R2+R3) I 

 IR.      =  (R1+R2+R3)

  R.       = R1+R2+R3

 Resistance  in  parallel connection:  

The  resistors  R1,  R2,  R3  are  connected  in  parallel  across  the  supply  voltage  “V”.  The  total current  flowing  through  the  circuit  is  denoted  as  “I”.  The  current  flowing  through  the  resistor R1, R2  and R3  is  I1,  I2, and  I3  respectively.   

                     I  =  V / R  (as  per  ohms  law)

                     I1  =  V1  / R1 

                     I2  =  V2  / R2 

                     I3 =  V3  / R3 

         V 1 = V2  =  V3  =  V  From the above  diagram  

                      I  =  I1+I2+I3 

                         =  V1  / R1  +  V2  /  R2  +  V3  / R3 

                         =  V / R1+  V/R2  +V/R3

                    I    = V (1/R1  +1/R2  +1/R3) 

              V / R  =  V (1/R1  +1/R2  +1/R3) 

                 1/R = 1/R1  +1/R2  +1/R3