Informational Encyclopedia

The property of a substance by which it restricts the flow of electricity (electrons) through it. Metals,acids and salts solutions are good conductors. Among metals, silver, copper and aluminium are very good conductors of electricity.When electrons flow through the molecules or the atoms of the conductor, collide to the other atoms and electrons and generate heat. Those elements which offer relatively greater difficulty  to the passage  of these flowing electrons are said to be poor conductors of electricity.

Dry wood, rubber,PVC (polyvinyl chloride) and glass are poor conductors examples. Good insulators are fibrous substances like paper and dry cotton, mineral oil free from acid and water.

Unit of resistance is ohm, it can be defined as " a conductor having a resistance of one ohm when it permits one ampere current to flow through it when one volt is impressed across its terminals. For high resistance insulators bigger units  are used. Its symbol is (omega) Ω.

Laws of resistance.

The resistance R offered by a conductor depends upon the following factors which are known as laws of resistance, which are 

1: It change direction as its length l.

2: It varies inversely as the cross-section A of the conductor.

3: It depends on the nature of the material.

4: It depends on the temperature of the conductor.

So we can say 

                             R = ρ . l/A

where ρ is a constant depending on the nature of the material of the conductor and is known as specific resistance or resistivity.

Specific resistance or resistivity of a material may be defined as the resistance between the opposite forces of a meter cube of that material.

S.I unit of resistivity is ohm-meter.(Ω.-m)

 Mathematically

                           ρ = A (meter²) x R (ohm)/ l (meter)

                      = AR/l 

                                  

                           

A simple voltaic cell shown in figure, It contains of copper plate (Anode) and a zinc plate (Cathode) placed in a dilute sulfuric acid stored in suitable vessel. The chemical action taken placed  within the cell causes the electrons to be removed from the copper plate and to be deposited on the zinc plate at the same time.

Transfer of these electrons is completed with the help of dilute sulfuric acid, which is named as electrolyte. Zinc side becomes negative side due to deposit of electrons and copper side act as a positive side due to removal of electrons. The maximum amount of electrons on the zinc side is being attracted by anode but is prevented from returning to it by the force set up by the chemical action within the cell.

When two electrodes are connected by a wire externally, then the electrons rush to the anode thereby equalizing the charge of the two electrodes,but due to the chemical reaction a continuous difference in the numbers of electrons on the two electrodes is maintained which keep up a continuous flow of current through the external circuit.The action of the cell is same as water pump working.

When zinc is charged negatively , it is said to be at negative potential with respect to electrolyte, whereas anode is to be said the positive with respect to electrolyte. So in conclusion the copper plate is to be at higher potential than zinc plate. The difference in potential is continuously managed through the chemical action going in the cell which supplies energy to maintain the potential difference.

Current  is  defined  As  current  motion  involving  charge  via a  conducting material.  The unit  involving  current  will be  ampere  while  charge  will be  measured  throughout  Coulombs. 

It can also be described as movement of electricity along a conductor. 

Direct  current or constant current  is actually   many  commonly found  throughout  homes  in the   application   regarding  electrical energy  kept   inside  batteries.  with   a great  DC circuit,  The sort of  voltage  along with the  direction  of   application   are generally  constant.  The level of  voltage  is usually  determined  through the  type  in  addition to  size  regarding  battery.  ones  direction  involving  current flow  is   additionally  constant and,  Just as   inside  AC circuits,  The sort of  current flow  is  determined  by the   fill up  resistance.

 Batteries convert chemical energy  to  electrical energy.  chemical energy  is actually   within  wet form,  Equally   Utilizing your  car battery,  as well as   within  dry  application   Equally   in  flashlight  in addition to  transistor-radio batteries.  several  batteries  are generally   made to   possibly be  recharged  via   a  AC source. Voltage  via   almost all  batteries, unless recharged,  will  gradually decrease. AC power  is actually  converted  for you to  DC power  pertaining to   a few   functionalities   for the  home. Your own  conversion  is actually   done   by   a good  device called  the  rectifier  or perhaps  current converter.

 Alternative current or time varying current can be defined as a   flow  of  electrons  that will  reverses  it is  direction  involving  flow  at  regular intervals  with   the  conductor.      

      The  range   connected with   whole  charge  The item  passes  in the course of   a great  arbitrary cross  section   of a  conducting material per unit second  will be  defined  just as one  Ampere.    

Mathematically

                                      I = Q/t  or Q = I.t

Where 

Q is symbol of charge in coulombs,(C)

I is the current in amperes (A)  

t is the time in second (s)

        Voltage attempts  to   Produce a  current flow,  as well as current  may  flow  no matter whether   ones  circuit  can be  complete. Voltage  will be  sometimes  stated  just like   the  'push'  or  'force'  of   electricity, it isn't really a force but this may help you to imagine what is happening. It is possible to have voltage without current, but current cannot flow without voltage.

A unit  involving  electrical pressure (or electromotive force)  of which  causes current  to be able to  flow  with   the  circuit.  individual  volt  is usually   The level of  pressure  necessary to  cause  one  ampere  of  current  to be able to  flow against  one  ohm  regarding  resistance.   

  A unit  involving  measure  with regard to  indicating  ones  electrical power applied  with   a great  circuit.  This really is   taken   coming from  multiplying  the current  (in amperes)  by the  electrical pressure (in volts)  in which  cause  That   for you to  flow.  watts = amperes x volts.