by arjun basnet

Chapter-1

Introduction

Matter:

Ø In the classical physics observed in everybody  life , matter is any substance that has mass and takes up space.

Ø Matter exists in state for  phases ; the classical solid , liquid and gas.

Ø Matter should not be confused with mass at the two are not the same in modern physics.

Ø Matter is it self a physical substance of which system may be composed , while mass is not a substance but rather a quantatiue property of matter and other substance or system.

          Molecule:

Ø A molecule is the smallest particle in a chemical element or compound that has the chemical properties of that element or compound.

Ø A molecule is one electrically neutral group of two or more atoms held together by chemical bond.

Ø Molecule can vary greatly in size and complexity .

Familiar molecule include water , consisting of two atoms and one oxygen atom (H2O). Fig: H20 (water)

 

Hydrogen                                                           Hydrogen

                                                Oxygen

          Atom:

Ø An atom is smallest contituent unit of ordinary matter that has the properties of a chemical element.

Ø Every solid , Liquid ,gas and plasma is composed of neutral or ionized atoms.

Ø Atom are very small ; typical size around 100 picometer (a ten billion of  matter in the short scales ).

Ø Every atom composed of a nucleus and one or   more electrons bound to the nucleus.

Charge:                                                                                                                       

Ø Charge may be defined as the quantity of unbalanced electricity in a body  (either positive or negative ) and construed as an excess or deficiency of electrons.

Ø Charge comes in two form , positive (+) and negative charge (-).

Ø Charge is conserved . This means that we cannot create or destroy change . Charge can change its form.

Electric charge:

Ø In physics, charge is also known as electric charge , electrical charge or electrostatic charge and symbolized Q.

Ø Electric charge it the physical property of matter that cause it to re experience a force when placed in an electromagnetic field.

Ø There are two types of electric charge : positive and negative (commonly carried by proton electrons respectively ).Like charge repel and unlike.

Current:

Ø Current is the flow of charge .

Ø Charge flows in a current .

Ø Current is reported as the number of charges per unit time passing through a boundary.

What causes current ?

Ø Charge object move in response to electric and magnetic forces.

Ø These force come from electric and magnetic field , which in turn comes from the position  and motion of other charge.

Electric current:

Ø An electric current is flow of electric charge .

Ø In electric circuit this change is often carried by moving electrons in a wire .

Ø It can also be carried by iron in an electronic and ionized gas (plasma).

Ø The SI unit for measuring an electric current is the amphere (which is the flow of electric charge across a surface at the rate of one coulomb per second.

Direct current (DC):

Ø Direct current (DC) is the unidirectional flow of electric charge.

Ø If the current flow on only one direction then it is called direct current or dc.

Ø Direct current is produced by source such as batteries , power supply ,thermocouple , solar cells or dynamos .

Ø Direct current may be flow in a conductor such as a wire but can also flow through semiconductor insulation or ion beams.

Ø Direct current is used to charged batteries and as power supply  for electrons.

Ø The diagram show as oscilloscopes screen displaying the signal from a dc supply.

                                      Figure of dc current

Application of Direct Current:

                                                       i.            Domestic

                                                    ii.            Automotive

                                                 iii.            Telecommunication

                                                  iv.            High voltage power transmission

                                                     v.            Other

Alternating current:

Ø If the current constantly change direction, then it is called alternating current or ac.

Ø Alternating current (AC) is an electric current which periodically reserve directions , where as direct current (DC) flows in only one direction .

Ø Audio and radio signals carried on electrical wire are also example of alternating current .

Ø The diagram shows an oscilloscope screen displaying the signal from ac supply.

 

                                                          Figure of ac current

                   Ac VS Dc current ( Alternating current and Direct current)

S.N	Alternating current(Ac)	Direct current (DC)
1.Amount of energy that can be carried.	Safe to transfer city distance and provide more power.	Voltage of Dc cannot travel very until it being to loss energy.
2.Frequency	The frequency of according current is 50 Hz or 60 Hz depending up on the country.	The frequency of Direct current is zero.
3.current	It is the current of magnitude varying with time.	It is the current of constant magnitude.
4.Direction	It reserve its direction while flowing in a current .	It flow in one direction in the current.
5.Passive parameter	Impedance	Resistance only.
6.Power factor	Lies between 0 and 1.	It is always 1.
7.Types	Sinusoidal , trope zooidal ,Triangular square.	Pure and pulsating.

         Basic parameter Of  Alternating current:

Ø In case of  sinusoidal wave form.

         

                             Figure of sinusoidal wave form

          Amplitude :

Ø Mathematically, the amplitude of a sine wave is the value of that same wave as its peak.

Ø However, when we speak of an ac power supply system it is more powerful to refer to the effective of current.

Frequency :

Ø Frequency in term of any regular waveform identifies the number of complete cycle it goes through in a fixed period of time.

Ø For standard measurement the period of time is one second ,so the frequency of the wave is commonly measurement in cycle per second(cycles sec and  in normal usage is expressed in unit of Hertz ( Hz)

Ø It is represent in mathematically equation by letter 'f''.

Wavelength :

Ø Wave length is very similar to period , except that wave length is measured in distance per cycle while period is measured in time per second.

Ø Wave length is denoted by 'f''.

Period :

Ø The amount of time required to complete one cycle of the wave form rather than the number of cycle per second of this time is called period.

Ø This is logically the reciprocal of frequency .

Ø P=1/f .

Peak value ( IP ):

                                     

Ø Referring to the figure , it is the maximum value  of voltage of (vp) or current ( IP ).

Ø The peak value applies to both positive and negative value of the cycle.

Peak-peak value :

 

Ø During each complex cycle of an ac there are always two maximum peak value , one for positive half- cycle of and the other for the negative half-cycle . The different between the peak  positive value and peak to peak value of sine wave

Instantaneous value :

Ø The instantaneous value of an alternating voltage or current is the value of voltage or current at one particular instant.

Ø The value may be zero if the the particular instant is the time in cycle at which the polarity of the voltage is chaning.

Average value:

Ø The average value of an alternating current or voltage is the average of all the instantaneous value during one alternation.

Ø Since the voltage increase from zero to peak value and decrease back to zero during one alternating , the average value must be same value between these who limits.

Root Mean Square value (RMSV):

Ø Circuit current and voltage in AC current are generally stated as root mean square or rms rather than by quoting the maximum value most mean square for a current is defined by IRMS =

OHM’S  lAWS :

Ø Ohm’s law state the current through a conductor between two point is directly proportional to the voltage across the two point.

Figure of ohms laws

I=v/r

                   Where,

Ø I, is the current through the conductor in units of amperes.

Ø V, is the voltage measure across the conductor in unit of volt.

Ø R, is the resistor of conductor in unit of ohms.

Kirchhoff’s  circuit law :

Ø Kirchhoff’s  circuit law are two equalities that deal with the current and potential difference in the lumped element model of electrical circuit.

*Kirchhoff’s current law (KCL):

Ø This law is also called Kirchhoff’s first law Kirchhoff’s point rule or Kirchhoff’s Junction rule ( or nodal rule ).

Ø The principle of conservation of electrical charge implies that :                    At any node ( Junction)  in a electrical circuit , the sum of current following into that nodel is equa; to the sum of current flowing out of that node.

                                                or

Ø The algebraic sum og current in a network of conductor meeting at a point is zero .

Ø I(existing) + I(entering) = 0

                                      Figure of KCl

The current entering any junction is equal to the current leving the junction i2 + 13 = i1 + i4

                   Uses :

Ø A matrix version of Kirchhoff’s current law is the basic of must circuit law is the basic of must circuit simulation software such as SPICE.

Ø Kirchhoff’s current law combined with ohms law is used is nodal analysis.

Ø KCL is applicable to any lumped network irrespective of the nature of the network  whether  unilateral or bilateral , active or passive linear or non-linear.

2. Kirchhoff’s Voltage Law :

Ø This is also called Kirchhoff’s second law , Kirchhoff’s loop ( or mesh) rule and Kirchhoff’s second rule .

Ø The principle of conservation of energy implies that                                         “ The directed sum of the electrical potential difference ( voltage ) around any closed  network  is zero.

Or

Ø “More simple , the sum of the emfs in any closed loop is equivalent to the  sum of potential drops in that loops .

                                      Or

Ø “The algebraic sum of the product of the resistor of the conductor and the currents in them in a closed loop is equal to the total emfs available in that loop.                                                                                               EMFS= ELECTRONIC MOTIVE FORCE

The sum of all the voltage around a loop is equal zero .

          i.e: v1 + v2 +v3 – v4 = 0