UNIT – I
DIRECT CURRENT CIRCUITS
1. Basic Concepts and Definitions ( I, V, P , E & Ohms law)
2. Basic Components of Electrical circuits (R, L & C)
2.1 Resistance , Inductance & Capacitance -Definitions , Symbol, Units, Abbreviation.
2.2 Resistance , Inductance & Capacitance depends upon factors
2.3 Basic Analysis of Resistance ,Inductance & Capacitance
2.4 Resistive Networks, Inductive Networks, Capacitive Networks
2.5 Resistance , Inductance & Capacitance - Equivalent Circuit
2.6 Star to Delta and Delta to Star Transformation
3. KCL and KVL
4. Mesh Analysis
5. Nodal Analysis
6. Superposition Theorem
7. Thevinins Theorem
8. Maximum Power Transfer Theorem
9. Types of Sources ( Energy Sources )
,(i) ELECTRICAL CURRENT: (ii) ELECTRICAL VOLTAGE (or) POTENTIAL DIFFERENCE
Definition: The flow of free electrons through a conducting material is Definition: The Potential Difference is the energy required to
called as Electrical Current move one coulomb of charge from one point to the other
Formula: (a) Constant Current
(b) Instantaneous Current Formula: (a) Constant Voltage :
W
Unit: It is measured in Ampere (A) V= joules/coulombs (or) Volt
Q
Abbreviation: Electric current is denoted by the letter i(t) or I.
(b) Instantaneous Voltage :
Vab = dw volt
Note: Current is always measured through a circuit element as shown in Fig dq
Where w is energy in joules (J)
q is charge in coulombs (C).
The voltage ab or simply V is
Unit: It is measured in volt (V).
Two types of currents:
1) A direct current (DC) is a current that remains constant with time.
2) An alternating current (AC) is a current that varies with time. Abbreviation: Electric Voltage is denoted by the letter
v(t) or V.
Note: Voltage is always measured across a circuit element as
shown in Fig.
(a) Direct current (DC) (b) Alternative current (AC)
, (iii) ELECTRICAL POWER: (iv) ELECTRICAL ENERGY :
Definition: The rate at which work is done in an electrical Definition: Energy is the capacity to do work in electrical circuit
circuit is called as Electrical Power
Formula: (a) constant Energy
Formula: : (a) constant Power: E = P * t Joules
E = V * I* t Joules
P = W
t E= I*R*I*t = I2 Rt Joules
P = VQ ---------- (since from V = W/Q) E = V * V*t = V2t Joules
t R R
P = V Q --------- (since from I = Q/t) Unit: It is measured in Joules (J)
t
P = V I Watts ---------- (a) Abbreviation: Electric Energy is denoted by the letter E.
From Eq (a) we get OHM’S LAW:
STATEMENT : Ohm’s law states that at constant temperature, the
P = (IR) I----------- (since from Ohms Law V=IR) current (I) flowing through the material is directly proportional to
voltage (V) across a conducting material.
P = I2 R Watts---------- (b) Mathematically,
I∞V
From Eq (a) we get I=V
R
P = V ( V) ----------- (since from Ohms Law V=IR) V=IR
R Where the constant of proportionality R is called the resistance of the
2
P = V Watts ---------- (c) material.
R The V-I relation for resistor according to Ohm’s law is depicted in Fig.
(b)Instantaneous Power :
Where p is power in watts (W), w is energy in joules (J),
and t is time in seconds (s). Fig. V-I Characteristics for resistor
Unit: It is measured in Watt (W) Limitations of Ohm’s Law:
1. Ohm’s law is not applicable to non-linear elements like diode,
Abbreviation: Electric Power, is denoted by the letter p(t) or P. transistor etc.
2. Ohm’s law is not applicable for non-metallic conductors like
silicon carbide
DIRECT CURRENT CIRCUITS
1. Basic Concepts and Definitions ( I, V, P , E & Ohms law)
2. Basic Components of Electrical circuits (R, L & C)
2.1 Resistance , Inductance & Capacitance -Definitions , Symbol, Units, Abbreviation.
2.2 Resistance , Inductance & Capacitance depends upon factors
2.3 Basic Analysis of Resistance ,Inductance & Capacitance
2.4 Resistive Networks, Inductive Networks, Capacitive Networks
2.5 Resistance , Inductance & Capacitance - Equivalent Circuit
2.6 Star to Delta and Delta to Star Transformation
3. KCL and KVL
4. Mesh Analysis
5. Nodal Analysis
6. Superposition Theorem
7. Thevinins Theorem
8. Maximum Power Transfer Theorem
9. Types of Sources ( Energy Sources )
,(i) ELECTRICAL CURRENT: (ii) ELECTRICAL VOLTAGE (or) POTENTIAL DIFFERENCE
Definition: The flow of free electrons through a conducting material is Definition: The Potential Difference is the energy required to
called as Electrical Current move one coulomb of charge from one point to the other
Formula: (a) Constant Current
(b) Instantaneous Current Formula: (a) Constant Voltage :
W
Unit: It is measured in Ampere (A) V= joules/coulombs (or) Volt
Q
Abbreviation: Electric current is denoted by the letter i(t) or I.
(b) Instantaneous Voltage :
Vab = dw volt
Note: Current is always measured through a circuit element as shown in Fig dq
Where w is energy in joules (J)
q is charge in coulombs (C).
The voltage ab or simply V is
Unit: It is measured in volt (V).
Two types of currents:
1) A direct current (DC) is a current that remains constant with time.
2) An alternating current (AC) is a current that varies with time. Abbreviation: Electric Voltage is denoted by the letter
v(t) or V.
Note: Voltage is always measured across a circuit element as
shown in Fig.
(a) Direct current (DC) (b) Alternative current (AC)
, (iii) ELECTRICAL POWER: (iv) ELECTRICAL ENERGY :
Definition: The rate at which work is done in an electrical Definition: Energy is the capacity to do work in electrical circuit
circuit is called as Electrical Power
Formula: (a) constant Energy
Formula: : (a) constant Power: E = P * t Joules
E = V * I* t Joules
P = W
t E= I*R*I*t = I2 Rt Joules
P = VQ ---------- (since from V = W/Q) E = V * V*t = V2t Joules
t R R
P = V Q --------- (since from I = Q/t) Unit: It is measured in Joules (J)
t
P = V I Watts ---------- (a) Abbreviation: Electric Energy is denoted by the letter E.
From Eq (a) we get OHM’S LAW:
STATEMENT : Ohm’s law states that at constant temperature, the
P = (IR) I----------- (since from Ohms Law V=IR) current (I) flowing through the material is directly proportional to
voltage (V) across a conducting material.
P = I2 R Watts---------- (b) Mathematically,
I∞V
From Eq (a) we get I=V
R
P = V ( V) ----------- (since from Ohms Law V=IR) V=IR
R Where the constant of proportionality R is called the resistance of the
2
P = V Watts ---------- (c) material.
R The V-I relation for resistor according to Ohm’s law is depicted in Fig.
(b)Instantaneous Power :
Where p is power in watts (W), w is energy in joules (J),
and t is time in seconds (s). Fig. V-I Characteristics for resistor
Unit: It is measured in Watt (W) Limitations of Ohm’s Law:
1. Ohm’s law is not applicable to non-linear elements like diode,
Abbreviation: Electric Power, is denoted by the letter p(t) or P. transistor etc.
2. Ohm’s law is not applicable for non-metallic conductors like
silicon carbide
