ECE203 Lecture 1

05, 07 July -2014
Lectures 3,4

ECE203 - Network Analysis - K.Jeya Prakash - Kalasalingam University

Charges two types: +ve, -ve
Force of attraction between them
Energy reqd. to overcome this for their
movement
Difference in P.E = P.D
P.D = Voltage
Energy W Joules
Voltage Volts = --------- = ---- = -------
Charge Q Coulomb

ECE203 - Network Analysis – K. Jeya Prakash - Kalasalingam University

Voltage applied – free e-s move in one direction
Movement of e-s from one end to other end
constitute current
Rate of flow of charges
Conventional current opposite to direction of e-s
movement
Q Coulomb
Current I Amperes = --------- = ------------
t Second
ECE203 - Network Analysis – K. Jeya Prakash - Kalasalingam University

Stored Work – Capacity for doing a work –
Energy
Rate of change of energy – Power
Work done W (Joules)
Power P watts = -------------- = --------------
Time t (Second)

Energy W Joules
Voltage Volts = --------- = ---- = -------
Charge Q Coulomb
Q Coulomb
Current I Amperes = --------- = ------------
t Second
Work done W (Joules)
Power P watts = -------------- = --------------
Time t (Second)

W Q
P = -----X-----
Q t
= V I

Network – Interconnection of two or more
elements
Circuit – Network with at-least one closed
path
Network elements – 4 types
Active / Passive
Unilateral / Bilateral
Linear / Non- linear
Lumped / Distributed

Active Elements – Generate Energy
Passive Elements – Cannot Generate Energy;
Dissipate/ Drop Energy

Bilateral– Same
voltage current
relation in both
directions Ex: R,L,C
Unilateral– Different
voltage current
relations in either
direction Ex: Diode

Linear Element: Voltage – Current
Relationship – a straight line through origin
Satisfies superposition property (i.e.)
principle of homogeneity and additivity
Ex: R, L, C
Non-linear Element: Does not satisify above
relationship
Ex: Semiconductor devices

Electrical properties assumed to be
located on small space of a circuit
Size small compared to wave
length of applied signal
Ex: Resistor, Capacitor, Inductor or
Transformer
Such systems function of time
alone
Electrical properties spread across
the entire circuit
Ex: Transmission Line
Function of time and one or more
spatial variables

Opposition to the passage of an electric current
through a material
Ohm’s Law
I = V/R
Current is directly proportional to the voltage and
inversely proportional to the total resistance of the
circuit
Unit of Resistance ‘Ohm’
Conductance – Opposition to Resistance
Allow passage of current through a material
Unit ‘mho’

Behaviour of a coil of wire in resisting any
change of electric current through the coil
Property of a conductor by which a change
in current flowing through it "induces"
(creates) a voltage (electromotive force) in
both the conductor itself (self-inductance)
and in any nearby conductors (mutual
inductance).

Arising from Faraday's
law, the inductance L
may be defined in terms
of the emf generated to
oppose a given change
in current:
The relationship
between the self-
inductance L of an
electrical circuit (in
henries), voltage, and
current is

V = L di/dt
di = 1/L x vdt
∫di = 1/L ∫v dt
i(t) – i(0) = 1/L ∫v
dt
i(t) = i(0) + 1/L ∫v
dt
Current in inductor
depends on
integral of voltage
across its
terminals and
initial current in
the coil

P = vi = Ldi/dt i
W = ∫p dt
= ∫ L i di/dt
= L i2 /2
Inductor store energy
even if voltage across
is zero
Never dissipates energy.
Only stores
Voltage across
inductor is zero, if
current through it is
constant
Small change in
current in zero time
gives infinite voltage
across the inductor

Ability of a body to store an electrical
charge
Two conducting surfaces separated by an
insulating medium
Conducting surfaces – Electrodes
Insulating medium – dielectric
Amount of charge per unit voltage -
Capacitance

Unit of capacitance – Farad
C= Q/V; C = q/v
i = C dv/dt
dv = 1/C x i dt
∫dv = 1/C ∫i dt
v(t) – v(0) = 1/C ∫i dt
v(t) = v(0) + 1/C ∫i dt
p = vi = v C dv/dt
W = ∫p dt = ½ Cv2
Current in a capacitor is zero if V is
constant
Open circuit to dc
Small change in voltage within zero
time gives infinite current
Even if current is zero, store finite
amount of energy
Pure capacitor never dissipate
energy
ECE203 - Network Analysis - K20-07-2014.Jeya Prakash - Kalasalingam University

Based on terminal voltage-current
characteristics, sources in a circuit –
Ideal Voltage source
Ideal Current Source
Classified further as
Independent Source
Dependent Source

Two terminal element in
which the voltage is
completely independent of
current through its terminals
Practical voltage sources
have internal resistance in
series => voltage decreases
as current increases

Two terminal element in
which current is
independent of voltage
across its terminals
Practical current sources
have internal resistance in
parallel => current falls as
voltage increases

Independent
sources: Voltage
and Current are
independent and
not affected by
other parts of the
circuit
Dependent Source:
Source voltage or
current is
dependent on the
voltage or current
existing at some
other parts of the
circuit

Dependent or
controlled sources
types:
Voltage Controlled
Voltage Source (VCVS)
Current Controlled
Voltage Source (CCVS)
Voltage Controlled
Current Source (VCCS)
Current Controlled
Current Source (CCCS)

Kirchhoff's circuit laws are two equalities that
deal with the current and potential difference
(commonly known as voltage) in the lumped
element model of electrical circuits
Corollaries of the Maxwell equations in the low-
frequency limit
Accurate for DC circuits, and for AC circuits at
frequencies where the wavelengths of
electromagnetic radiation are very large
compared to the circuits

Also called Kirchhoff's first law, Kirchhoff's point rule,
or Kirchhoff's junction rule (or nodal rule)
At any node (junction) in an electrical circuit, the
sum of currents flowing into that node is equal to the
sum of currents flowing out of that node,
or: The algebraic sum of currents in a network of
conductors meeting at a point is zero.
Based on principle of conservation of electric charge

Also called Kirchhoff's second law, Kirchhoff's loop (or mesh) rule,
and Kirchhoff's second rule
The directed sum of the electrical potential differences (voltage)
around any closed network is zero,
or: More simply, the sum of the emfs in any closed loop is
equivalent to the sum of the potential drops in that loop,
or: The algebraic sum of the products of the resistances of
the conductors and the currents in them in a closed loop is equal
to the total emf available in that loop.
Based on the conservation of energy whereby voltage is defined
as the energy per unit charge.

Applicable only to lumped network models
KCL is valid only if the total electric charge,
Q , remains constant in the region being
considered
KVL is based on the assumption that there is
no fluctuating magnetic field linking the
closed loop.

Series circuit – Voltage divider
Same current flows; Voltage drops
proportional to value of resistors/impedance;
Different voltage from single source; So
called voltage divider
Power in series circuit: Sum of powers in
each resistor in series

Current from source divides in all branches
of parallel circuit; So called current divider
Power in parallel circuit: Sum of powers in
each resistor in parallel

ECE203 Lecture 1

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