Basic Concept of Circuit and Network Elements..........2

Network and Circuit

Network is defined as the an electric network have any possible interconnections of electric circuit elements or branches.

Visit this Link to read about basic concept of Circuit Elements

An electric circuit is close energized network.

"Every circuit is a network but all networks are not circuit".

Types of  basic Network:

• Lumped Network
• Distributed Network

Lumped Network:

A network is said to be lumped network in which Resistors, Capacitors and inductors can be represented physically separated.

In lumped network we have assumed that magnetic field is associated with inductance and electric field with capacitance, but we are neglected the effect of interaction between the two fields which can not actually be isolated.

Distributed Network:

In which Resistors, Capacitors and inductors can not be electrically separated and individually isolated as separate elements.

e.g. A Transmission line is Distributed Network.

Charge:

We can define the charge by Atomic theory in easy and conceptual way.

An Atom is composed of a positively charged nucleus surrounded by the negative charged electrons. In neutral atom the total charge of the nucleus is equal to the total charge of the electrons.

when electrons are removed from a substance then that substance becomes positively charged.

A substance with excess of electrons is negatively charged.

Note: The basic unit of charge is the charge of electron, the electron has a charge of  1.6021 * 10^ -19

          The MKS unit of charge is Coulomb.

Current:

The phenomenon of transferring charge in a circuit from one point to another point is called Electric Current.

" Charge in motion is called current".

A random motion of electrons in a metal does not constitute a current unless there is a net transfer of charge with time.

The Current Equation is 

                               i= dq/dt            q= charge in coulombs, t= time in seconds, i= Current in Amperes.

 As shown in above figure:

the current in wires is actually due to negative charge not positive charge motion. the direction of flow of Electron is from negative terminal to positive terminal and wholes means positive charges flow from positive to negative terminal. that is why the current direction is same of positive charge direction but opposite of direction of electron.

Thus, The current flows in opposite direction to the flow of negative charge (electron).

Voltage:

To move the electrons from one point to another in particular direction external force is required, in a circuit external force is provided by emf. it is also known as voltage source.

                                                                  v= dw/dq

         where a differential amount of charge dq is given as a differential increase in energy dw. The quantity per unit charge is called voltage.

A voltage can exist between a pair of electrical terminals whether a current is flowing or not.

Power:

If potential is multiplied by the current then what we get is power.

                                        P= vi

                                        P= dw/dq * dq/dt

                                        P = dw/dt

 Power is also defined as the a time rate of change in energy is called power. Thus the Power is the product of potential and current.

Energy:

The capacity to do the work is called Energy.