WHAT ELECTRIC CURRENT IS....

CONDUCTOR OF ELECTRICITY

           All matter does not conduct electricity well.It is well known that metals conduct well.The fact can be well explained by the theory of free electrons.Metals have valencies 1,2 or 3; that means atoms of metal have 1,2 or 3 electrons at the outermost shell.So metallic atoms have a tendency to detach the outermost electrons from the atom to acquire the electronic structure like the "Noble Gas". Due to heat energy these electron become free from the atom.As a result electrons and positively charged atoms (Cations) are generated.These electrons can move freely within the metallic surface and are called "the FREE ELECTRON"). These electrons give rise to current electricity.

          If we apply potential difference at the ends of a conductor then these free electrons moves from lower potential to the higher potential region.This gives rise to electric current from higher to lower potential.There are two types of electrical flow- 1.DC

                                                 2.AC

DC CURRENT :

         The electric current in which current flows in only one direction irrespective of time ; then the flow is known as DC( Direct Current). Here the potential difference does not vary with time, also the current does not vary.

AC CURRENT :

         The electric flow where the magnitude of current as well as of the potential difference changes sinusoidally with change in time is called the AC (Alternating Current). Instant magnitude of AC Voltage and current can be represent as

       V(t) = Vo Sin (wt)

And E(t) = Eo Sin (wt)

       Here Eo And Vo is called the peak value; w is called angular frequency.

           Time gap, between two consecutive positive or negative peaks, is called "TIME PERIOD". Reciprocal of this time period is called the frequency. The  frequency of a proper AC signal is 50/sec.

EXPLANATION OF AC WAVEFORM

             Famous scientist Michael Faraday said that If there is relative motion between a magnetic field and closed conducting loop then electric current is generated. This happens as magnetic flux density linked with the loop changes continuously with time.

          The following figure how the current is generated due to movement of a magnet into a loop

           If "B" be the magnetic field flux density, "A" be the area of the loop, θ be the angle between the magnetic lines of force and the perpendicular to the loop and "n" be the no. of turns of the loop then magnetic flux linked with the loop is 

                             Φ = nBA Cos(θ)   ................................(1)

       In a dynamo a magnetic shaft rotates within a rectangular coil.Thus the angle θ changes from 0 to 2л

    Then the induced emf linked with the loop is , 

                                    E = - dΦ/dt

                                       =  nBASin(θ) dθ/dt

                                       =  nBAωSinθ 

                                                           Where ω is the angular frequency of rotation                                                             =  Eo Sinθ .............................(2)

 MORE ABOUT AC

       1.AVERAGE VALUE

                           The average value of DC is constant but average value of AC averaged over the full cycle is zero.The average is done as follows :

       <E> =( ∫E(t) dt )/ ∫dt

               =(∫EoSinθdt)/ ∫dt

               =(∫Eo Sin (ωt) dt)/ ∫dt   , the limit of both the int. being  0 to T (time period)

               =0

        Average value of AC emf is non zero over a half cycle.In that case both of the above integration is done with lower limit 0 and upper limit T/2.

       2. RMS VALUE

         The rms value of AC emf is given as 

         Erms =√( ∫Eo²Sin²θ dt/ ∫dt) 

                 =√( ∫Eo²Sin² (ωt)dt/ ∫dt)         limit of integrations 0 to T

                  =(Eo) /√ 2

        *NB>* Thus we can understand why AC is more dangerous than DC. Here we see the peak value of AC emf Eo= √2 Erms. When we speak about 220 Volt AC then 220 Volt is its rms value. Therefore the peak value is 220√2=311 Volt (aprox.). But in DC 220 Volt means its peak value is 220 Volt.                      

    Though 220 Volt DC is not good for us, 220 Volt AC is more harmful.

  

DISCOVERY OF ELECTRICITY

HISTORY:

           About 600 BC Greek philosopher Thales observed that if AMBER (a type of resin of pine) is rubbed with fur  then it attracts paper cut into pieces.It was not then understood that why this happen?But in no time man started application of it.They found it a great way to stick balloons on the wall. Pet cats were then a useful fellow for their hairy body.

EXPLANATION

             The fact was explained later in the 17th century AD. The observation of Thales was explained as statical electrification.All matter consists of atoms.Atom contains two types of charged particle Protons and Electrons and neutral particles the Neutrons and a few elementary particles.Protons and Neutrons forms the center, the Nucleus and the Electrons moves round the nucleus in orbits.Fur the position of electron from the nucleus less the force of attraction, due to the nucleus, is on it.Thus the electrons at the furthest orbit are very loosely bounded to the atom.If we rub any matter with then these electrons may free from atom due to mechanical energy.The free electrons are received by one of the materials that were rubbed; thus both of them becomes electrified.Electrified materials can attract oppositely charged materials or neutral materials.So they attracts pieces of paper, pith ball etc.

         

             If the material that is rubbed is an insulator then the charged developed can not move through it stays there for a long time.Hence this is called STATICAL ELECTRICITY. If we rub a Conductor with wool or fur then we never see such things; because they conducts the charge developed due to rubbing.

VOLTA'S  DISCOVERY    :

              Scientist Volta was the first to develop current electricity.He did it by using 'oil of vitriol' and two types of metallic plates - one of copper (Cu) and the other zinc (Zn).  He made multiple layer of Zinc and Copper by placing one after another and separating them by  cloth and felt wet in 'oil of vitriol"  (Sulfuric Acid ) .This led to invent the first electric cell, called the Simple Voltaic Cell.

FURTHER DEVELOPMENT :

  

         
      Then as time passes more developed cells were designed. A few of them are The Leclance cell, Lead Acid cell etc.But with these cells we cannot fulfill the great requirement of electricity.

FARADAY'S DISCOVERY :

     Michael Faraday discovered that "If there is relative motion in between a magnet and a closed loop then electric current is generated in the loop.The magnitude of the current increases with velocity of movement , number of turns of the loop.

                   DYNAMO:

                             Dynamo is a device designed to generate current electricity.There is a rectangular coil      made of insulated copper wire and a strong magnet.The magnet actually forms the armature of the device.If the Armature is rotated around its axis then we get current electricity.Following is a simple diagram of a Dynamo.

              Here we get AC current.The magnitude of voltage (also current) changes sinusoidally with time.This happens because the number of the lines of force of the magnet that passes through the coil changes with time (As the is rectangular and the magnet is in circular motion).

   

             In power generation centers we actually revolve the shaft i.e. the armature of a dynamo.If we do that by Heat Then it called Thermal Power, If by Water flow then Hydel Power , If by Atomic Energy to Heat to Electric Energy then Atomic Power.            

 

Hard Disk Drive Failure :-

HDD (Hard Disk Drive) Failure or Boot Disk Failure 

(A) Here user must run the CMOS set-up for "IDE HDD auto detection".

(B) If the HDD is not detected, then user should check the connectivity of HDD controller.

(C) After fixing up the connection properly, if again the HDD is not detected then user can change the IDE channel, i.e. (that is) from IDE 0 to IDE 1.

(D) If the HDD Is Detected but system is not booting from c:/>, in that case user can first try with the transferring system booting from A:/>.

(E) If C drive display "Invalid Drive", in that case user should run the "Fdisk" command to create the partition.

(F) If the partition already exist then user can just try by making the primary Dos partition active.

(G) If the partition is made properly and system is transferred, then user should scan the entire HDD for virus problem.

(H) User also run the diagnostic tools like NDD, NE, DE, DM for checking the HDD track '0' and other sectors.

(I) After attempting all the possible reasons user must check the master-slave jumper setting for proper configuration and must check battery voltage for CMOS set-up. Even the existing HDD can be checked at another PC. In case for the problem of on-board IDE Chanel, the problem can be solved temporarily by adding an IDE-IO controller card at ISA slot of the motherboard. (Here, on-board Chanel should be disabled from CMOS set-up.) 

HOW TO AMPLIFY ELECTRIC CURRENT :-

WHAT IS AN AMPLIFIER?

An Amplifier is a device that can increase or decrease a signal.We can make an amplifier with a TRANSISTOR. A Transistor operated in CE mode can be useful for the purpose.

  

TRANSISTOR : Transistors are of two types- 1.npn & 2. pnp. Transistors are made imposing impurity to pure semiconductor.If we can impose p-type impurity from both sides to a n-type semiconductor we get a pnp type transistor ; and if we can impose n-type impurity from both side to a p-type semiconductor we get a npn  transistor.

  

 OPERATION of a TRANSISTOR : There are three modes of operations of a transistor :1.CE 2.CB 3.CC. To make an Amplifier we use CE mode operation.The circuit configuration is shown below :

Here we have two types of important characteristics of which output characteristic is needed for Amplifier.

OUTPUT CHARACTERISTICS :

    The output characteristic is the graphical representation of Collector current (Ic) Vs Collector-Emitter Voltage (Vce) keeping the input current (The Base current) fixed or constant.The following figure shows such a characteristic :

    The black st. line AB is called a load line .Using the biasing of the load line we prepare an Amplifier.The colored lines represent different input currents.If a small AC signal is fed to input bias then it slightly changes the input current as a result output current also changes.Input current is of the order micro-Ampere but the output current is of the order of milli-Ampere 1000 times of the input.So if take out put we get Amplified current that was fed to the input.   

 

CD-ROM Drive Is Prompted In Dos Mode But Not In Windows :-

(A) Firstly user must run the CMOS set-up for the auto detection of CD-ROM drive. If it is 'ok', then user should copy the "MSCDEXE.EXE" file from c:\WINDOWS\COMMAND> to c:\>. (It's not that all the BIOS detect CD-ROM at 'Auto Detection'.)

(B) The slave jumper is not detected by the WINDOWS default driver of CD-ROM for which the WINDOWS driver can be installed from CD-ROM driver for WINDOWS. Driver is installed by user which is comming with CD-ROM driver.

                                      CD-ROM Drive

(C) User can also check the new hardware wizard from control panel for detection of CD-ROM controler.

(D) The IRQ No. Range (reserved - 12/13/14/15) from power management set-up can be altered for accessing of CD-ROM under WINDOWS.