Basic Electrical Circuits

1
Basic Electrical Circuits Machines (EE-107)

• Course Teacher
• Shaheena Noor
• Assistant Professor
• Computer Engineering Department
• Sir Syed University of Engineering Technology.

2
Basic Components and Electrical Circuits

• The basic goals of this chapter is to understand
  the basic electrical quantities (with associated
  unit), Relationship between charge, current,
  voltage and power, Difference between dependent
  and independent sources (both voltage and
  current) and detailed knowledge of the behavior
  of the resistor and Ohms law.

3
Basic Components and Electric Circuits

• Components
• Electric Circuits

4
Charge, Current, Voltage and Power

• Charge
• Definition ? It is define in terms of ampere by
  counting the total charge that passes through a
  wire in one second.
• Symbol ? Q or q
• Unit of Measurement ? Coulomb
• Unit Abbreviated ? C

5
Charge, Current, Voltage and Power

• Current
• Definition ? Transfer of charge OR transfer
  energy from one point to another.
• For Example ? Power transmission line (practical
  example of transfer energy)

6
Charge, Current, Voltage and Power

• It has numerical value and direction.
• Correct Representation ?
• Two methods of representation for the exact same
  current.
• Improper/incomplete definitions of a current

3A
- 3A
Figure a
Figure b
i1(t)
7
Charge, Current, Voltage and Power

• Symbol ? I or i
• Unit of Measurement ? Ampere (Amp)
• Unit Abbreviated ? A

8
Charge, Current, Voltage and Power

• Types of Current
• A current that is constant in time is termed as
  Direct Current or simply dc.

9
Charge, Current, Voltage and Power

• Types of Current
• Current that vary sinusoidally with time current
  of this form are present in normal household
  circuits. Such a current is often referred to as
  Alternating current or ac.

i
t
10
Charge, Current, Voltage and Power

• Types of Current
• Exponential Currents Damped Sinusoidal current
  (will discuss later)

11
Drill Problem 2.3 (page 11)

• In the wire of the given figure, electrons are
  moving left to right to create a current of 1mA.
  Determine I1 and I2.

I1
I2
12
Charge, Current, Voltage and Power

• Voltage
• Consider an object with 2 terminals.
• Two paths by which current may enter or leave the
  element.

A general 2-terminal circuit element
A
B
13
Charge, Current, Voltage and Power

• Symbol ? V or v or E
• Unit of Measurement ? Volts
• Unit Abbreviated ? V

14
Charge, Current, Voltage and Power

• Inadequate definitions of a voltage
• A correct definition

A correct definition includes both a symbol for
the variable and a plus-minus symbol pair.
15
Charge, Current, Voltage and Power

• Voltage

Fig (a)
Fig (b)
Fig (d)
Fig (c)
Fig (d)
16
Charge, Current, Voltage and Power

• Important Point
• A voltage can exist between a pair of electrical
  terminals whether a current is flowing or not.
• For example ? An automobile battery has a voltage
  of 12V across its terminals even if nothing is
  connected to the terminals.

17
Drill Problem 2.4 (page 13)

• For the given figure if V1 17V. Determine V2.

-
V2

18
Charge, Current, Voltage and Power

• Power
• Definition ?Power is a measure of how much work
  can be performed in a given amount of time.
• In electric circuits, power is a function of both
  voltage and current.
• P VI
• Symbol ? P or p
• Unit of Measurement ? Watt
• Unit Abbreviated ? W

19
Drill Problem 2.5 (page 15)

• Find the power being absorbed by the circuit
  element.

20
Drill Problem 2.6 (page 15)

• Find the power being generated by the circuit
  element.

21
Drill Problem 2.7 (page 15)

• Find the power being delivered by the circuit
  element at t 5ms.

8e-100t V

-
3.2A
22
Voltage and Current Sources

• Independent Source
• Dependent Source

23
Voltage and Current Sources

• Independent Voltage Source

-
Vs
24
Voltage and Current Sources

• Independent Voltage Source
• Other Representations

-
Vs
Battery Symbol
Ac voltage source
25
Voltage and Current Sources

• Independent Current Source

Is
26
Voltage and Current Sources

• Dependent Sources
• Also referred as controlled source.
• It is determined by a voltage or current existing
  at some other location in the system being
  analyzed.
• Symbol ? A diamond Shape

27
Voltage and Current Sources

• Four Different types of Dependent Sources

-
-
Kix
gVx
KVx
rix
Figure (a)
Figure (b)
Figure (c)
Figure (d)
28
Drill Problem 2.8 (page 18)

• Find the power absorbed by each element in the
  circuit given below.

- -Vx
5A
8 V -
12 V -
20 V -
- 12V
8 V -
0.25Vx
7 A
2 A
8 A
29
Ohms Law

• The voltage across conducting materials is
  directly proportional to the current flowing
  through the material.
• V I R
• Power P V I
• Power Absorption

30
Drill Problem 2.9, 2.10 (Page 23)

• With reference to V and I defined in the given
  figure, compute the following quantities.
• 2.9 R if I -1.6mA and V -6.3V
• 2.10 The absorbed power if V -6.3V and R 21?

figure