Electric Charge I Electric Current | Voltage


                It is the basic property of matter carried by elementary particles that causes it to experience a force when placed in magnetic or electric field.  There are two types of electric charge: positive and negative (commonly carried by protons and electrons respectively). Like charges repel each other and unlike charges attract each other. An object with an absence of net charge is referred to as neutral. The Charge is neither created nor destroyed.The negative charge of each electron is  equal to that of the positive charge of each protonSome of the atoms in the surface layer of a glass rod get positively charged by rubbing it with a silk cloth by lossing electrons, leaving a net positive charge because of the unneutralized protons of their nuclei. A negatively charged object has an excess of electrons on its surface. similarly a positively charged object has excess of protons on its surface.It is denoted by “q” and its SI unit is coulomb “C”and is defined as the amount of electric charge that flows through a cross section of a conductor in an electric circuit during each second when the current has a value of one ampere.

 Various properties of charge include the following:

  • Additivity of Electric Charge
  • Conservation of Electric Charge
  • Quantization of Electric Charge

In any isolated system, Electric charge is conserved, which means the net electric charge of the system is constant. The algebraic sum of the fundamental charges in any isolated system remains the same.

Net charge in a system

                                q = ne + np


Where e = charge of electron = -1.602 x 10-19 C

                p = charge of proton = 1.602 x 10-19 C

                n = number of electron/protons

                                1 C  = 6.242 x 1018 e

Electric current

                it is defined as the rate of change of charge through specified area. the direction of the current in electric circuits is taken as the direction of positive charge flow, the direction opposite to the actual electron drift. When so defined the current is called conventional current.


 Where “I” is the current,

dq = change in charge,

dt = change in time (seconds) 

The SI Unit of current is ampere “ A”


                it is defined as amount of potential energy between two points in a circuit. one point has more charge than another. This difference in charge between two points is called voltage. The SI unit of voltage is volt “ V”.

 When describing voltage, current, and resistance, a common analogy is a water tank. In this analogy, charge is represented by the water amount, voltage is represented by the water pressure, and current is represented by the water flow. So for this analogy, remember:

  • Water = Charge
  • Pressure = Voltage
  • Flow = Current

Consider a water tank at a certain height above the ground. At the bottom of this tank there is a hose.


The pressure at the end of the hose can represent voltage. The water in the tank represents charge. The more water in the tank, the higher the charge, the more pressure is measured at the end of the hose.We can think of this tank as a battery, a place where we store a certain amount of energy and then release it. If we drain our tank a certain amount, the pressure created at the end of the hose goes down. We can think of this as decreasing voltage, like when a flashlight gets dimmer as the batteries run down. There is also a decrease in the amount of water that will flow through the hose. Less pressure means less water is flowing, which brings us to current.

Read Also

02.Principle and Construction of DC generator  

03.Electric Circuit | Terms Related to Electric Circuit | What is Electric Circuit

04.Electric Charge | Electric Current | Voltage

05.Series and Parallel Combination of Resistances


07.Electrical Thumb Rules

08.Kirchhoff’s Laws

09.Where does the reactive power Go?

10.Why Transformer is not Connected to DC


12.Series and parallel Combination of Capacitors

13.Types of Resistors

14.Voltage divider Rule and Current divider Rule

15. Lightning Arrester

16. Losses in Transmission and distribution

17.Charging and Discharging of Capacitor

18.Electrical Earthing

19. Methods of Electrical Earthing

20.Calculating the Number of earthing rods/Pipes required


22.Series and Parallel Combination of inductors

23.Current Source and Voltage Source

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