7/27/2019 Electrical Engineering Definitions
1/34
Electrical Engineering Definitions
SI units
Electric Charge, Electrostatic Force, Electric
and Magnetic Fields
Electric Voltage, Current, and Power
DC and AC sources
Conductors, Resistance, Capacitance
Ohms Law
7/27/2019 Electrical Engineering Definitions
2/34
Currently, there are two main sets of measurement standards in use
The U.S Customary System
The International System (SI for short)
The primary system of measure for the world is the SI system often
referred to as the metric system
The scientific and engineering community use the SI system, so it isimportant to learn the system
7/27/2019 Electrical Engineering Definitions
3/34
Some commonly used prefixes for the international
system of units
Prefix Symbol Power of 10 Prefix Symbol Power of 10
exa E deci d
peta P centi c
tera T milli mgiga G micro
mega M nano n
kilo k pico phecto h femto f
deka da atto a
1810
1510
12
109
10
610
3
102
10
110
110
210
3
10
610
910
12
10
1510
1810
PEN
7/27/2019 Electrical Engineering Definitions
4/34
The seven basic SI units
Measured Quantity Unit Symbol
Length Meter m
Mass Kilogram kgTime Second s
Electric Current Ampere A
Thermodynamic Temperature Kelvin KAmount of a Substance Mole mol
Luminous Intensity Candela cd
7/27/2019 Electrical Engineering Definitions
5/34
7/27/2019 Electrical Engineering Definitions
6/34
7/27/2019 Electrical Engineering Definitions
7/34
Example finding net charge:
What is the magnitude of charge, in coulombs, of 756.23 x 1017
electrons?
18
number of electrons
6.24 10 electrons/Cnetq
x=
17
18
756.23x10 electrons
6.24 10 electrons/C
netq
x
=
12.12netq C=
7/27/2019 Electrical Engineering Definitions
8/34
Electrical Charge
To characterize electrical charge behavior we must start at the atom
which consist of
1. Proton(s): positive charges
2. Neutron(s): neutral charges
3. Electron(s): negative charges
Charge properties
1. Like charges repel one another
2. Unlike charges attract one another3. The force of repulsion or attraction obeys the inverse square law
EXAMPLE 4.1
http://example4.1.jnt/http://example4.1.jnt/7/27/2019 Electrical Engineering Definitions
9/34
A atom that has the same number of positive particles (protons)
and negative particles (electrons) has a net neutral charge.
-
-
+N
N+
-
N+
N
-
-
+N
N+
-
N+
N
7/27/2019 Electrical Engineering Definitions
10/34
If an atom loses an electron, it has a net positive charge
-
+N
N+
-
N+
N
--
+N
N+
-
N+
N
-
7/27/2019 Electrical Engineering Definitions
11/34
Once an electron is removed from an atom, which requires
some form of work, we are left with a positively charged atom
and a free, negatively charged, electron
The free electron may
1. Be captured by a nearby positive atom
2. Remain free and migrate to the surface of the material
which occurs because like charges repel
Note: option 2 assumes the energy applied to dislodge the
electron from the atom was not sufficient to completely ionize
the electron from the material
7/27/2019 Electrical Engineering Definitions
12/34
7/27/2019 Electrical Engineering Definitions
13/34
The repulsion and attraction phenomena of charge can be
best explained by looking at the equation for the force
present between two charges, or Coulombs law
Electrostatic Force
Electrostatic Force is the force exerted by one body ofcharge on another. This force can be calculated for
simple point charges by using the following equation.
F - is the force between the charges, q1 and q2
r - is the distance of separationk - is a proportionality constant = 8.99 x 109 Nm2/C2
- is a unit vector pointing from q1 to q2
EXAMPLE 4.2
122
21
rF r
qqk=
12r
7/27/2019 Electrical Engineering Definitions
14/34
The Electrostatic Force depends on the presence of at least
two charges a fixed distance apart.
We can generalize the force exerted by a single point charge
by defining a field, known as the Electric Field..
Electric Field
Note the units are in Newton/Coulomb or force/unit charge
0q
FE =
This is in terms of the force a test charge would experience whenplaced in the electric field produced by other charges.
7/27/2019 Electrical Engineering Definitions
15/34
Graphically representing Electric Field lines
++
1. Field lines originate on a positive
charge and terminate on a
negative charge. If there is no
negative charge to terminate on,
the lines will continue out to infinity
2. The number of field lines isproportional to the magnitude of
the net charge
3. The density of the field lines at agiven point is proportional to the
magnitude of the field at that point
7/27/2019 Electrical Engineering Definitions
16/34
Electric Current
How is moving charge is described, or how do we quantify the amount ofcharge we can move through a wire connected to a battery.
Electric Current
Electric Current, symbolized by I, is the quantitative measure of the
flow rate of electric charge carriers. It is measured by determining the
number of coulombs of charge that pass a specific point in the period
of time. The unit of electric current is the Ampere.
dq CoulombsI Ampere
dt Second = = =
7/27/2019 Electrical Engineering Definitions
17/34
Example of current
A piece of wire is connected across the terminals of a battery for a
period of 3 seconds. During this time, it is determined that 18
coulombs of charge move through the wire. What is the current in
the wire while it is connected to the battery terminals?
18 63
CI ASec
= =
dq
I dt=
7/27/2019 Electrical Engineering Definitions
18/34
Magnetic Field
All changing Electrical fields have an
accompanying Magnetic Field. The magnetic
field is the result of charge movement or
Current . If a current exist you have an
associated magnetic field.
The magnetic field produced by a current is
related the magnitude of the current and thegeometry and other physical characteristics
of the conductor the current is in.
BATTERY-WIRE COIL-NAIL
7/27/2019 Electrical Engineering Definitions
19/34
Magnetic Flux due to a Current
(a)(a)
(b)(b)
(a)(a)
(b)(b)
2
7
0
(Weber)
cross-sectional area of the coil
permeability of core material, in freespace
4 x 10 /
number of turns in the coil
length of the coil
current in the coil
cm
c
N AI
l
A
H m
N
l
I
=
=
=
= =
=
=
=
7/27/2019 Electrical Engineering Definitions
20/34
7/27/2019 Electrical Engineering Definitions
21/34
Voltage (potential): is defined as electrical potential energyper unit charge.
Voltage can be thought of as a measure of stored electrical
energy that has the ability to do work, such as moving other
charges via an electric field.
This stored energy is equal in magnitude to the work done to
move a charge from point A to B where A and B are of
different potentials.
When we talk about Voltage, or potential difference, we are
really describing the voltage difference between two points
W JouleVolt
q Coulomb
= =
Definition of Electric Voltage
V lt E l
7/27/2019 Electrical Engineering Definitions
22/34
Voltage Example
Any measure of potential must include a reference point
7/27/2019 Electrical Engineering Definitions
23/34
Electrical Power
Electrical power is a measure of the electrical work, or energy used, per
unit time, the following relationship is known as Watts Law
Instantaneous Power
The instantaneous power, of an electrical device is defined as
the work that is done per unit of time. In terms of the voltage, V,
and current, I ,
EXAMPLE 4.3
WattSecond
JouleIVP ===
http://example4.3.jnt/http://example4.3.jnt/7/27/2019 Electrical Engineering Definitions
24/34
DC Signal
Has a constant voltage and current, neglecting the changes
occurring during power on and power off.
Common sources
Batteries
DC power supply
constant
constant
V
I
=
=t
C S
7/27/2019 Electrical Engineering Definitions
25/34
AC Signal
Alternating Current
Alternating Current is a fluctuating current that is associated with a
changing potential difference (AC Voltage). The most common
alternating current pattern is associated with a sinusoidal change involtage.
Common Sources
Household power
Signal generator
Peak, peak-to-peak
RMS
EXAMPLE 4.4
( ) sin(2 )v t A ft =
t
7/27/2019 Electrical Engineering Definitions
26/34
Resistance
Physically resistance is a measure of a materialsopposition to charge flow or current.
Resistance is measured in units called Ohms
The higher the resistance of a material, the more potential
difference is required to maintain a current.
The resistance of a material is temperature dependant.
7/27/2019 Electrical Engineering Definitions
27/34
Figure 4.6. This water pipe illustrates the concept of resistance. The smaller center section of the pipe
has a larger resistance to water flow.
Resistive MaterialResistive Material
Figure 4.7 The electrical equivalent of the water-based example given in figure 4.6. A resistive material connected to
two conduct ing copper wires.
7/27/2019 Electrical Engineering Definitions
28/34
Type Characteristics
Carbon Least expensive, wide available range of values
and tolerances, typically used for low power and
low frequency applications
Metal Film Used in higher voltage applications and where
high precision is called for. These devices exhibit
internal capacitance, due to the metal film
deposits, which can cause changes in the device
impedance at higher frequencies.
Wirewound Used for medium to high voltage applications
requiring high power handling. However due to
their geometry they exhibit high inductive
properties, making them suitable only for lower
frequency applications.
Numeric 1 Numeric 2 Numeric 3 Multiplier ToleranceColor
7/27/2019 Electrical Engineering Definitions
29/34
Numeric 1 Numeric 2 Numeric 3 Multiplier Tolerance
Black 0 0 0 1
Brown 1 1 1 10 1%
Red 2 2 2 100 2%
Orange 3 3 3 1KYellow 4 4 4 10K
Green 5 5 5 100K 0.5%
Blue 6 6 6 1M 0.25%
Violet 7 7 7 10M 0.10
Gray 8 8 8 0.05%White 9 9 9
Gold 0.1 5%
Silver 0.01 10%
Color
Four band Resistor
The first two bands indicate numericvalues.
The third band is the multiplier.
The fourth band is the tolerance.
Example:
[Red2][Green5][Yellow10k][Silver10%]
Resistor value = 25 x 10k = 250 kOhm 10%
Five band Resistor (High precision)
The first three bands are numerical
values.
The fourth band is the multiplier.
The fifth band is the tolerance.
Example:
[Blue6][Gray8][Red2][Blue1M][Brown1%]
Resistor value = 682 x 1M = 682 MOhm 1%
7/27/2019 Electrical Engineering Definitions
30/34
Capacitance
Capacitance
Capacitance, simply stated is the amount of charge that a
capacitor is capable of holding per unit of voltage applied.
Where Q is the net charge, V is the voltage, and C is the
capacitance. Units are Farads (F).
V
QC =
Capacitoris a device capable of storing energy in an electrical field
Energy Stored by a capacitor:
Units of Joules
21
2U CV=
7/27/2019 Electrical Engineering Definitions
31/34
Example of a parallel plate capacitor
+ -
Plate
Separation
distance, d
+ -
Plate
Separation
distance, d
Figure 4.8. A conceptual example of a basic
capacitor. A capacitor consists of two metal
plates separated by an insulating d ielectric
material.
+
+
+
+
+
+
+
+
-
-
-
-
-
-
-
-
PlateSeparation
Distance, d
Electric Field Lines
+
+
+
+
+
+
+
+
-
-
-
-
-
-
-
-
PlateSeparation
Distance, d
Electric Field Lines
Figure 4.9. An illust ration of the electric field
lines existing between the plates of a capacitor.
The energy that is stored in a capacitor is stored
in this electric field.
d
xAC
)F/m1085.8( 12=
7/27/2019 Electrical Engineering Definitions
32/34
Type CharacteristicsPaper Cheap, low to high voltage, low frequency, low
capacitance/volume, non-precision general
purpose applications
Mica Very stable, high precision, good for tunedcircuit applications, high capacitance/volume,
low leakage current
Tantalum or Aluminum Polarized, largest capacitance/volume, high
loss, commonly used for power supply filtering.
Ceramic High voltage, available in both low loss and high
loss, Capacitor tolerance can run from +100%
to -20%
Codes see: http://wiki.xtronics.com/index.php/Capacitor_Codes
http://wiki.xtronics.com/index.php/Capacitor_Codeshttp://wiki.xtronics.com/index.php/Capacitor_Codes7/27/2019 Electrical Engineering Definitions
33/34
There exist a nice relationship that ties together the quantities
Voltage, Current, and Resistance known as Ohms Law
Ohms Law
Ohms Law gives a relationship between a materialsresistance, R, the voltage across it, V, and the current flowing
through it, I.
IRV=
Ohms law gives us an equation we can use to find voltage, current, orresistance if we know two of the quantities. MEMORIZE IT
EXAMPLE 4.5
CHECK 4.5
http://example4.5.jnt/http://example4.5.jnt/7/27/2019 Electrical Engineering Definitions
34/34
What You should know
1. Basic SI units
2. How charges behave (repel, attract)
3. Definition of current
4. Definition of voltage
5. Definition of resistance6. Ohms law
7. Watts law
8. Difference between a DC and AC signal9. How to find peak, peak-to-peak, and RMS voltage
values
Top Related