bee

1. BASIC ELECTRICAL ENGINEERING
UNIT 1
06/07/2020 1

2. Circuit Theory Laws
This presentation contains
• voltage, current,
• Conventional and electric current
• Ohm’s Law.
• Kirchhoff’s law
i.KCL
ii.KVL
Active and passive components
combinations
i.series
ii.parallel 2

3. Electric Charge
The charge of an electron and that of a proton are equal in magnitude.
Electrical charge is an
electrical property of matter that exists because of an excess of
deficiency of electrons, which is
symbolized by Q.

5. Electricity – The Basics
An understanding of the basics of
electricity requires the
understanding of three
fundamental concepts.
•Voltage
•Current
5

6. Voltage, Current
2/20/2013
Andre Ampere
1775-1836
French Physicist
Current – Current is the rate of flow of
electrical charge through an electronic
circuit. The direction of a current is
opposite to the direction of electron flow.
Current is measured in AMPERES
(AMPS).
6

7. Voltage
2/20/2013
Alessandro Volta
1745-1827
Italian Physicist
Voltage – Voltage is the electrical force that
causes current to flow in a circuit. It is
measured in VOLTS.
7

8. Current Flow
• Conventional Current
assumes that current flows
out of the positive side of
the battery, through the
circuit, and back to the
negative side of the battery.
• Electron Flow is that the
electrons flow out of the
negative side of the battery,
through the circuit, and back
to the positive side of the
battery.
2/20/2013
Electron
Flow
Conventional
Current
8

9. Ohm’s Law
• Defines the relationship between voltage, current, and
resistance in an electric circuit
• Ohm’s Law:
At constant temperature Current in a resistor varies in
direct proportion to the voltage applied to it and is
inversely proportional to the resistance.
• Stated mathematically:
2/20/2013
R
V
I 
Where: I is the current (amperes)
V is the potential difference (volts)
R is the resistance (ohms)
V
I R
+ -
9

10. Ohm’s Law Triangle
2/20/2013
V
I R
)A,amperes(
R
V
I 
),ohms(
I
V
R 
)V,volts(RIV 
V
I R
V
I R
10

11. Limitations of Ohm’s law:
• Not applicable for non linear devices.
• Eg. Zener diode.
• can’t be applicable for non metallic conductors.
• Eg. Human body.
• Holds good only at constant temperature.
2/20/2013 11

12. Kirchoff’s Laws
2/20/2013
Kirchhoff’s Voltage Law (KVL):
The algebraic sum of all of the
voltage in a closed circuit is equal to zero.
(or)
total sum of potential drop in a circuit
=total sum of potential rise in the circuit.
∑v=0
12

13. Kirchoff’s Current Law (KCL):
•The algebraic sum of the currents
meeting at a junction in a closed circuit is
zero.
•The sum of current entering into the
junction = the sum of current leaving
from the junction.
•∑i=0
2/20/2013
Gustav Kirchhoff
1824-1887
German Physicist
13

14. Electrical Components
•They can be either
•Active - energy sources
•Eg. Battery, generator.
•Passive- energy consumers
•Eg. Resistor, inductor, capacitor.
2/20/2013 14

15. RESISTOR
Resistance is the electrical property of which it opposes the flow of current
in an electrical circuit.
It is represented in ohms Ω
R=𝞺L/A
2/20/2013 15

16. CAPACITOR
• Capacitor is an electrical element which stores energy in the
form of electrostatic field.
• It stores energy during positive half cycle and emits energy
during negative half cycle.
• The average energy stored in a capacitor is zero
• C=q/v
2/20/2013 16

17. 2/20/2013
 Mathematical relation
 Where
i= current that in capacitor in (ampere)
C= capacitance in (farad)
= rated of change of voltage.
= rate of change of time in second
i
t
C
dv
d

.
dv
dv
dt
capacitor
17

18. 2/20/2013
Inductor
 The behavior of inductor is associated with
magnetic field &electrical field
 It is a storage element.
 energy is stored in the form of electromagnetic
field.
 Its unit is Henry(H)
18

19. 2/20/2013
Where
V= voltage between inductor in (volt)
L= inductor in (Henry)
= rate of change of current flow in ampere
= rate of change of time in second
V
t
L
di
d

dt
di
Circuit
symbol:-
19

20. Series Circuits(end to end)
• If the resistors are connected end to end.
• Current is the same for all series components.
2/20/2013 20

21. 2/20/2013 21

22. Series Circuits
Characteristics of a series circuit
The current flowing through every series
component is equal.
The sum of all of the voltage drops (VR1 + VR2
+ VR2) is equal to the total applied voltage
(VT). This is called Kirchhoff’s Voltage Law.
The total resistance (RT) is equal to the sum
of all of the resistances (i.e., R1 + R2 + R3).
2/20/2013 22

23. If any break takes place at any point in a circuit there will not
be any current flow.
High Voltage cannot be connected by this method.
Not practicable for residential wirings.
operation is not efficient.
Disadvantagesof series combination

24. Total Power in Series Circuits
The total power is the sum of the power
dissipated in each part of the circuit or:
PT = P1 + P2 + ...+ etc
P = V x I
P = I2 x R
P = V2 / R
Where p is power,
I is the current,
V is the potential difference,
R resistance

25.  Series combination is used in lamps of low voltages are to be operated
on the main supply.
 E.g. Decoration lights.
 When a load of low voltage is to be operated on a high voltage supply, a
fixed value of resistance is connected in series with the load.
 Used in fan regulators.
Applications of Series Combination:

26. • One end of all the resistors are joined to the common point
and the other ends are joined to other common point.
• Voltage source is connected between the common points
2/20/2013 26

27. PARALLEL COMBINATIONS
current (I) inversely proportional to
resistance (R)
2/20/2013 27

28. Parallel Circuits
Characteristics of a Parallel Circuit:
•The voltage across every parallel
component is equal.
•The total resistance (RT) is equal to the
reciprocal of the sum of the individual
resistors.
2/20/2013
321
T
321T
R
1
R
1
R
1
1
R
R
1
R
1
R
1
R
1


28

29. Advantages of parallel circuits
The electrical appliances of different power rating may be rated for the same
voltage.
It will not affect other branches.
Total resistance is less.

30. Disadvantages of parallel circuits:
•For parallel Calculating total resistance is quite
difficult.
•Because,
•Rp = 1 / RT = 1/R1 + 1/R2 + 1/R3 + ... Etc
• they require more connecting wires

31. Applications of parallel circuits
• All electrical appliances are connected in parallel.
• Electrical wirings in cinema halls, auditoriums
• parallel combinations are used in residential house wiring.
• It is more efficient

32. 2/20/2013
Parallel circuit Series circuits
Current is different Current is same
Potential difference is same Potential difference is
different
More than one path for
current flow
Only one path for current
flow.
Difference between parallel & series
32