Short Notes: Network Theory | Short Notes for Electronics and Communication - Electronics and Communication Engineering (ECE) PDF Download

 Page 1


Network Theory 
Current: Electric current is the time rate of change of charge flow. 
• Charge transferred between time t
o 
and t
Sign Convention: A negative current of –5A flowing in one direction is same as a 
current of +5A in opposite direction. 
Voltage: Voltage or potential difference is the energy required to move a unit 
charge through an element, measured in volts. 
Power: It is time rate of expending or absorbing energy. 
• Law of conservation of energy must be obeyed in any electric circuit.
• Algebraic sum of power in a circuit, at any instant of time, must be zero.
i.e. SP = 0 
Circuit Elements: 
Passive element: If it is not capable of delivering energy, then it is passive 
element. Example: Resistor, Inductor, and Capacitor 
Page 2


Network Theory 
Current: Electric current is the time rate of change of charge flow. 
• Charge transferred between time t
o 
and t
Sign Convention: A negative current of –5A flowing in one direction is same as a 
current of +5A in opposite direction. 
Voltage: Voltage or potential difference is the energy required to move a unit 
charge through an element, measured in volts. 
Power: It is time rate of expending or absorbing energy. 
• Law of conservation of energy must be obeyed in any electric circuit.
• Algebraic sum of power in a circuit, at any instant of time, must be zero.
i.e. SP = 0 
Circuit Elements: 
Passive element: If it is not capable of delivering energy, then it is passive 
element. Example: Resistor, Inductor, and Capacitor 
 
Active element: If an element is capable of delivering energy independently, then 
it is called active element. Example: Voltage source, and Current source. 
 
 
Linear and Non linear elements: If voltage and current across an element are 
related to each other through a constant coefficient then the element is called as 
linear element otherwise it is called as non-linear. 
Unidirectional and Bidirectional: When elements characteristics are independent 
of direction of current then element is called bi-directional element otherwise it is 
called as unidirectional.  
• R, L & C are bidirectional 
• Diode is a unidirectional element. 
• Voltage and current sources are also unidirectional elements. 
• Every linear element should obey the bi-directional property but vice versa 
as is not necessary. 
 
Resistor: Linear and bilateral (conduct from both direction)  
• In time domain V(t) = I(t)R 
• In s domain: V(s) = RI(s) 
 
• l = length of conductor, ?= resistivity, A = area of cross section 
Page 3


Network Theory 
Current: Electric current is the time rate of change of charge flow. 
• Charge transferred between time t
o 
and t
Sign Convention: A negative current of –5A flowing in one direction is same as a 
current of +5A in opposite direction. 
Voltage: Voltage or potential difference is the energy required to move a unit 
charge through an element, measured in volts. 
Power: It is time rate of expending or absorbing energy. 
• Law of conservation of energy must be obeyed in any electric circuit.
• Algebraic sum of power in a circuit, at any instant of time, must be zero.
i.e. SP = 0 
Circuit Elements: 
Passive element: If it is not capable of delivering energy, then it is passive 
element. Example: Resistor, Inductor, and Capacitor 
 
Active element: If an element is capable of delivering energy independently, then 
it is called active element. Example: Voltage source, and Current source. 
 
 
Linear and Non linear elements: If voltage and current across an element are 
related to each other through a constant coefficient then the element is called as 
linear element otherwise it is called as non-linear. 
Unidirectional and Bidirectional: When elements characteristics are independent 
of direction of current then element is called bi-directional element otherwise it is 
called as unidirectional.  
• R, L & C are bidirectional 
• Diode is a unidirectional element. 
• Voltage and current sources are also unidirectional elements. 
• Every linear element should obey the bi-directional property but vice versa 
as is not necessary. 
 
Resistor: Linear and bilateral (conduct from both direction)  
• In time domain V(t) = I(t)R 
• In s domain: V(s) = RI(s) 
 
• l = length of conductor, ?= resistivity, A = area of cross section 
• Extension of wire to n times results in increase in resistance: 
 
• Compression of wire results in decrease in resistance: 
 
 
Capacitor: All capacitors are linear and bilateral, except electrolytic capacitor 
which is unilateral. 
• Time Domain: 
 
• In s-domain: 
 
• Capacitor doesn’t allow sudden change of voltage, until impulse of 
current is applied. 
• It stores energy in the form of electric field and power dissipation in ideal 
capacitor is zero.  
Impedance:  
 
Inductor: Linear and bilinear element 
 
• Inductor doesn’t allowed sudden change of current, until impulse of 
voltage is applied. It stores energy in the form of magnetic field. 
• Power dissipation in ideal inductor is zero. 
 
Page 4


Network Theory 
Current: Electric current is the time rate of change of charge flow. 
• Charge transferred between time t
o 
and t
Sign Convention: A negative current of –5A flowing in one direction is same as a 
current of +5A in opposite direction. 
Voltage: Voltage or potential difference is the energy required to move a unit 
charge through an element, measured in volts. 
Power: It is time rate of expending or absorbing energy. 
• Law of conservation of energy must be obeyed in any electric circuit.
• Algebraic sum of power in a circuit, at any instant of time, must be zero.
i.e. SP = 0 
Circuit Elements: 
Passive element: If it is not capable of delivering energy, then it is passive 
element. Example: Resistor, Inductor, and Capacitor 
 
Active element: If an element is capable of delivering energy independently, then 
it is called active element. Example: Voltage source, and Current source. 
 
 
Linear and Non linear elements: If voltage and current across an element are 
related to each other through a constant coefficient then the element is called as 
linear element otherwise it is called as non-linear. 
Unidirectional and Bidirectional: When elements characteristics are independent 
of direction of current then element is called bi-directional element otherwise it is 
called as unidirectional.  
• R, L & C are bidirectional 
• Diode is a unidirectional element. 
• Voltage and current sources are also unidirectional elements. 
• Every linear element should obey the bi-directional property but vice versa 
as is not necessary. 
 
Resistor: Linear and bilateral (conduct from both direction)  
• In time domain V(t) = I(t)R 
• In s domain: V(s) = RI(s) 
 
• l = length of conductor, ?= resistivity, A = area of cross section 
• Extension of wire to n times results in increase in resistance: 
 
• Compression of wire results in decrease in resistance: 
 
 
Capacitor: All capacitors are linear and bilateral, except electrolytic capacitor 
which is unilateral. 
• Time Domain: 
 
• In s-domain: 
 
• Capacitor doesn’t allow sudden change of voltage, until impulse of 
current is applied. 
• It stores energy in the form of electric field and power dissipation in ideal 
capacitor is zero.  
Impedance:  
 
Inductor: Linear and bilinear element 
 
• Inductor doesn’t allowed sudden change of current, until impulse of 
voltage is applied. It stores energy in the form of magnetic field. 
• Power dissipation in ideal inductor is zero. 
 
 
 
 
 
Page 5


Network Theory 
Current: Electric current is the time rate of change of charge flow. 
• Charge transferred between time t
o 
and t
Sign Convention: A negative current of –5A flowing in one direction is same as a 
current of +5A in opposite direction. 
Voltage: Voltage or potential difference is the energy required to move a unit 
charge through an element, measured in volts. 
Power: It is time rate of expending or absorbing energy. 
• Law of conservation of energy must be obeyed in any electric circuit.
• Algebraic sum of power in a circuit, at any instant of time, must be zero.
i.e. SP = 0 
Circuit Elements: 
Passive element: If it is not capable of delivering energy, then it is passive 
element. Example: Resistor, Inductor, and Capacitor 
 
Active element: If an element is capable of delivering energy independently, then 
it is called active element. Example: Voltage source, and Current source. 
 
 
Linear and Non linear elements: If voltage and current across an element are 
related to each other through a constant coefficient then the element is called as 
linear element otherwise it is called as non-linear. 
Unidirectional and Bidirectional: When elements characteristics are independent 
of direction of current then element is called bi-directional element otherwise it is 
called as unidirectional.  
• R, L & C are bidirectional 
• Diode is a unidirectional element. 
• Voltage and current sources are also unidirectional elements. 
• Every linear element should obey the bi-directional property but vice versa 
as is not necessary. 
 
Resistor: Linear and bilateral (conduct from both direction)  
• In time domain V(t) = I(t)R 
• In s domain: V(s) = RI(s) 
 
• l = length of conductor, ?= resistivity, A = area of cross section 
• Extension of wire to n times results in increase in resistance: 
 
• Compression of wire results in decrease in resistance: 
 
 
Capacitor: All capacitors are linear and bilateral, except electrolytic capacitor 
which is unilateral. 
• Time Domain: 
 
• In s-domain: 
 
• Capacitor doesn’t allow sudden change of voltage, until impulse of 
current is applied. 
• It stores energy in the form of electric field and power dissipation in ideal 
capacitor is zero.  
Impedance:  
 
Inductor: Linear and bilinear element 
 
• Inductor doesn’t allowed sudden change of current, until impulse of 
voltage is applied. It stores energy in the form of magnetic field. 
• Power dissipation in ideal inductor is zero. 
 
 
 
 
 
 
 
Mesh Analysis: 
• Path - A set of element that may be traversed in order, without passing thru 
the same node twice 
• Loop - a closed path 
• Mesh - A loop that does not contain any other loop within it 
• Planar Circuit - A circuit that may be drawn on a plane surface in such a way 
that there are no branch crossovers 
• Non-Planar Circuit - A circuit that is not planar, i.e, some branch(es) pass 
over some other branch(es) (Can not use Mesh Analysis) 
 
Transformer: 4 terminal or 2-port devices. 
 
 
• N
1 > 
N
2 
: Step down transformer 
 
• N
2  
> N
1 
: Step up transformer