basic electrical

1. Basic Electrical and Electronics
Engineering
EE 104
L-T-P (2-1-0)
Lecture #1 (20110105)

2. Course Instructors
• Dr. Vipul Singh
• Analog
• Dr. Abhinav Kranti
• Digital

3. Circuit
Def: A circuit is an arrangement of electric or electronic
components that perform a useful operation/function.
Some of the common circuit components are the following:• Voltage/Current Sources.
• Resistors.
• Inductors.
• Capacitors.
• Operational Amplifiers.
• Transistors etc.

4. Circuit Classification
 Closed Circuit:
Path is complete
and therefore
current flows.
 Open Circuit:
Path is
incomplete, thus
no current flows.

5. Switch symbols
More than often the flow of current in a circuit is
controlled by using a switch. Some of the common types
of Switches used in circuits are shown below:-
Knife or gate
switch
Push-button
switch
(Push to ON)
Push-button
switch
(Push to OFF)

6. Current flow convention
e
e
I
e
e
e
e
By Convention the direction of flow of
current is opposite to the direction of flow of
electrons.

7. Ideal circuit element
i
+
v
Circuit element
A circuit element is ideal if its voltage and current
are related by
 constant of proportionality
 a differential or integral representation
An ideal circuit element has linear behavior.

8. Ohm’s Law
Ohm’s law states that the current flowing through a
resistor is directly proportional to the voltage applied
across its terminals.
v
R
i
+
v
-
i
A resistance conducts current from one node to the
other and in the process, voltage drop occurs across
the element in the direction of the current flow.
V = iR

9. Circuit terminologies
• A branch represents a single element viz. a
voltage source or a resistor.
• A node is a point of connection between two or
more branches.
• A loop is any closed path in a circuit.
For example in the circuit shown
adjacently the total number of
branches is 4, number of nodes
is 3 and the number of loops is
3.

10. Kirchhoff’s Voltage Law (KVL)
Kirchhoff’s voltage law (KVL) states that around any
loop within a circuit the algebraic sum of voltages
across various elements is zero.
i
Applying KVL we have:
2 KΩ
10 V
+ V 1
+
V2
-
3 KΩ
10 - V1  V2  0
 10  i  2000 - i  3000  0
 i  2 mA

11. Kirchhoff’s Current Law (KCL)
Kirchhoff’s current law (KCL) states that around any
node of a circuit the algebraic sum of all the currents
is zero.
Applying KCL @ node 1 we have:
i
+
V2
-
i2
5 KΩ
2 KΩ
10 V
+
V1
-
i1
i  (-i1 )  (-i 2 )  0
 i  i1  i 2
Applying KVL in loop 1 & 2 we have:
i1  5 mA; i 2  2 mA

12. Series Circuit
Resistances are said to be connected in series if
there is only one path for the current to get from one
point to another through these resistances.
→ Resistances connected in series have same
current flowing through them.
V - iR 1 - iR 2 - iR 3  0
i
V
R1
R2
R3
V
  R eff  R 1  R 2  R 3 
i
Voltage drop across R1
is given by
V
VR1  iR 1  VR1 
R 1 Voltage divider rule
R 1  R 2  R 3 

13. Starting from node 1 and traversing the loop in a
clockwise direction, plot potential as a function of
distance.
i
R1
R2
V
R3
1
V
VR1
VR2
R3 has the highest
value amongst
these resistances
VR3
position

14. Parallel Circuit
i
i1
V
i2
R1
R2
V
V  i1R 1  i1 
R1
Resistances are said to be
connected in parallel when the
voltage across each of them is
the same.
i  i1  i 2
similarly
V
V  i2R 2  i2 
R2
 1
V V
i
1
1 
i 

 
 
R R 

R1 R 2
V R eff  1
2 
Current divider rule
R2
i1 
i
R 1  R 2 
R1
i2 
i
R 1  R 2 

15. Example
Problem: Determine the current in the resistor R3, in
the circuit shown below
i1
V0
i2
i3
R2
R1
R3
 i1 
V0

 R 2R 3 
 R1  


R 2  R 3 



Since R2 and R3 are in parallel by current divider rule we have
R2
R2
V0
i3 
i1  i 3 
R 2  R 3 
R 2  R 3  
 R 2R 3 
 R1  


R 2  R 3 




16. Voltage and Current Sources
V volts
Ξ V volts +
-
Ideal voltage source
An ideal voltage source is a
device that produces a fixed
potential difference across its
terminals regardless of what
is connected to it.
I Amperes
Ideal current source
An ideal current source is a
device that moves a fixed
amount of current in the
direction indicated by the
arrow regardless of what is
connected to it.
These are all Independent current/voltage sources

17. Dependent Sources
Def: An ideal dependent current or voltage source is a
source whose value depends upon some variable
(usually a voltage or current) in the circuit to which
the source belongs. Dependent sources are also
called controlled sources.
2v1
+
-
3i1
+
-
4i1
5v1
Voltage dependent Current dependent Current dependent Voltage dependent
Voltage source
Voltage source
Current source
Current source

18. Example
Problem: The circuit shown below contains a current
dependent voltage source. Determine the current i in the
circuit, also find the voltage drop across 3.5 Ω resistor.
2V +
-
2Ω
Applying KVL we have
+
-
i
0.5i
3.5 Ω
2 - 2i  0.5i - 3.5i  0
 i  0.4 A
Let voltage drop across 3.5 Ω resistor be v2
 v 2  0.4  3.5  1.4 V

19. Combining Sources
v2
+
-
v1
a
a
v1+v2
+
-
Voltage sources
in series add up
b
b
a
a
i1
+
-
Current sources
add up in parallel
i1+i2
i2
b
b

20. Wheatstone Bridge
i3
R1
i1
i2
R3
(i1-i3) R
0
Vs  i 2 R 2  (i1 - i 3  i 2 )R 4  0(ii)
R4
(i1-i3+i2)
R2
VS
Vs  i1R1  i 3R 3  0(i)
Applying KVL in loop 1 & 2 we get
 i1R1  (i1 - i 3 )R 0  i 2 R 2  0(iii)
 i 3R 3  (i1 - i 3  i 2 )R 4  (i1 - i 3 )R 0  0(iv)
Under balanced condition (i1-i3) is zero, thus substituting the
same in eqn 3 & 4 we get
R1 R 3

R2 R4

21. Power Dissipated by a Resistor
Energy dissipated by a resistance in time t is given by
E  i 2 Rt
The rate at which energy is converted or supplied is
defined as power,
E 2
P
i R
t
Thus for an ideal resistor, Power is given by
V2
P  i 2R  i  V 
R