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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 
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FAQs on Short Notes: Network Theory - Short Notes for Electronics and Communication - Electronics and Communication Engineering (ECE)

1. What is Network Theory in Electronics and Communication Engineering?
Ans. Network Theory in Electronics and Communication Engineering deals with the study of electrical circuits consisting of interconnected electrical components.
2. What are the key concepts in Network Theory?
Ans. Key concepts in Network Theory include Ohm's Law, Kirchhoff's Laws, Thevenin's Theorem, Norton's Theorem, and various circuit analysis techniques.
3. How is Network Theory applied in real-world applications?
Ans. Network Theory is applied in designing and analyzing electronic circuits, communication systems, power systems, and control systems in various industries.
4. What are the different types of networks in Network Theory?
Ans. The different types of networks in Network Theory include linear networks, passive networks, active networks, and time-varying networks.
5. What are the common problems faced in studying Network Theory?
Ans. Common problems faced in studying Network Theory include understanding complex circuit diagrams, solving circuit equations, and applying different theorems effectively in circuit analysis.
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