EE 419 – Basic Electrical Engineering

Electricity

• The invisible energy that constitutes the flow of electrons in a closed circuit to do work is called
‘electricity’.It is a form of energy that can be easily converted to any other form. Previously, it
was thought that electricity is a matter which flows through the circuit to do work. However,
now it has been established that electricity constitutes the flow of electrons in the circuit, and
in this process, a work is done. It is form of energy. The Greatest discoveries of man that come
from the Greek word “electron” which means amber. Electricity is all about electrons, which
are the fundamental cause of electricity.

Two Main Types of Electricity

• Static Electricity - involves electrons that are moved from one place to another, usually by
rubbing or brushing. Static Electricity is nothing but the contact between equal amount of
protons and electrons (positively and negatively charged subatomic particles). In order to make
this friction work the particles are supposed to be of opposite nature (+,-). If two same-kind
particles i.e. positive-positive or negative-negative, it would then be called as a ‘Non-friction.
• Current Electricity - involves the flow of electrons in a conductor. Current Electricity is a flow
of electric charge across an electrical field. This current is lead through a conductor. The
conductors are generally of two types, Good and Bad conductors. Good conductors are the
ones which let the electric charge flow through them (Copper wires) and the bad conductors
are the ones which resists the electric charge (Wood). The constant flow of electric charge
causes the conductor to heat up very often.

The Shocking history of Electricity

• Around 600 BC Greeks found that by rubbing a hard fossilized resin (Amber) against a fur cloth,
it would attract particles of straw. This strange effect remained a mystery for over 2000 years.

Two Thousand Years Later

• Around 1600, William Gilbert, a physician who lived in London at the time of Queen Elizabeth I
and Shakespeare, studied magnetic phenomena and demonstrated that the Earth itself was a
huge magnet, by means of his "terrella" experiment. He also studied the attraction produced
when materials were rubbed, and named it the "electric" attraction. From that came the word
"electricity" and all others derived from it.

WILLIAM GILBERT

• Father of electricity
• The word “electricity” was coined by Gilbert, who based it on the Greek word for amber.
BENJAMIN FRANKLIN

• In 1752, Franklin proved that lightning and the spark from amber were one and the same thing.
This story is a familiar one, in which Franklin fastened an iron spike to a silken kite, which he
flew during a thunderstorm, while holding the end of the kite string by an iron key. When
lightning flashed, a tiny spark jumped from the key to his wrist. The experiment proved
Franklin's theory, but was extremely dangerous - he could easily have been killed.

GALVANI AND VOLTA

• In 1786, Luigi Galvani, an Italian professor of medicine, found that when the leg of a dead frog
was touched by a metal knife, the leg twitched violently. Galvani thought that the muscles of
the frog must contain electricity.

• By 1792, another Italian scientist, Alessandro Volta, disagreed: he realized that the main
factors in Galvani's discovery were the two different metals - the steel knife and the tin plate -
upon which the frog was lying. Volta showed that when moisture comes between two different
metals, electricity is created.

• This led him to invent the first electric battery, the voltaic pile, which he made from thin sheets
of copper and zinc separated by moist pasteboard.

• In this way, a new kind of electricity was discovered, electricity that flowed steadily like a
current of water instead of discharging itself in a single spark or shock.

• Volta showed that electricity could be made to travel from one place to another by wire,
thereby making an important contribution to the science of electricity. The unit of electrical
potential, the Volt, is named after him.

MICHAEL FARADAY

• The credit for generating electric current on a practical scale goes to the famous English
scientist, Michael Faraday. Faraday was greatly interested in the invention of the
electromagnet, but his brilliant mind took earlier experiments still further. If electricity could
produce magnetism, why couldn't magnetism produce electricity?

• In 1831, Faraday found the solution. Electricity could be produced through magnetism by
motion. He discovered that when a magnet was moved inside a coil of copper wire, a tiny
electric current flows through the wire. Of course, by today's standards, Faraday's electric
generator was crude (and provided only a small electric current), but he had discovered the first
method of generating electricity by means of motion in a magnetic field.

• Faraday also realized that the electric force is transmitted by an electric field.
JAMES WATT

• When Edison's generator was coupled with Watt's steam engine, large scale electricity
generation became a practical proposition. James Watt, the Scottish inventor of the steam
condensing engine, was born in 1736. His improvements to steam engines were patented over
a period of 15 years, starting in 1769 and his name was given to the electric unit of power, the
Watt.

ANDRE MARIE AMPERE

• Andre Marie Ampere, a French mathematician who devoted himself to the study of electricity
and magnetism, was the first to explain the electro-dynamic theory. A permanent memorial to
Ampere is the use of his name for the unit of electric current.

GEORGE OHM

• George Simon Ohm, a German mathematician and physicist, was a college teacher in Cologne
when in 1827 he published, "The Galvanic Circuit Investigated Mathematically". His theories
were coldly received by German scientists, but his research was recognized in Britain and he
was awarded the Copley Medal in 1841. His name has been given to the unit of electrical
resistance.

HOW IS ELECTRICITY PRODUCED?

A. Electricity Produced from Frictional Energy (Static Electricity)

• Frictional Electricity is the least important of all methods for the production of electricity. It
can be produced by rubbing certain dissimilar materials together. One application of static
electricity is in a device used in atomic research called Van de Graaff generator.

B. Electricity produced from Pressure

• Electricity produced from pressure is called piezoelectricity, which is produced by certain

crystalline materials such as quartz and barium titanate.

• If a crystal made of this material is placed between two metal plates and pressure is exerted on
the plates, an electric charge will be develop but the amount of charge will depend on the
amount of pressure exerted.

C. Electricity Produced from Heat

• The amount of charge produced depends on the difference in temperature between junction
and the opposite ends of two wires. A greater temperature difference results in a greater
charge. Electricity is produced by heating the junction of a thermocouple.
D. Electricity Produced from Chemical Reaction

• Electric cells are electricity produced by chemical reactions.

E. Electricity Produced from Light

• The electricity is produced by light striking photosensitive materials. These materials release
electrons when excited by light under the right conditions. These releases of electrons are
called photoelectric effect.

F. Electricity Produced from Magnetism

• Electricity produced by relative movement of a magnet and a wire that result in the cutting of
lines of force. The amount of electricity produced will depend on:
a) the number of turns in coil
b) the speed with which relative motions of the coil and the
magnet take place
c) the strength of the magnet

QUICK REVIEW OF THE ATOM

• Matter is made up of atoms

• Atoms are made of nucleons (called protons and neutrons) and electrons
• Protons have a positive charge, neutrons have no charge, electrons have a negative charge
• The charges of protons and electrons are equal and opposite

ATOMS ARE EVERYWHERE

• Electrons move in and out of fixed pathways around the nucleus

• Changing the number of electrons in a particular type of atom creates an ion of that atom
On the Move

• Electrons in the outer rings or shells of atoms are bound more loosely to the nucleus
• Such electrons tend to break free from the nucleus and wander around amongst other nearby
atoms
• Such electrons are called free electrons

MATTER

• Anything that occupy space and has weight

ELEMENT

• A substance that cannot be decomposed any farther by chemical reaction

ATOM

• Smallest part that an element can be reduced to and still keeping the chemical properties of the
element. It is the smallest building block of matter.

COMPOUND

• A combination of two or more elements.

MOLECULE

• It is the smallest particle that a compound can be reduced to before it breaks down to its
elements.

ELECTRONS

• Negatively charged particles that revolve around the nucleus of an atom. Electron is one of the
lightest particles with a known mass.
• The mass of electron is about 9.11 x 10-31 kg.

PROTONS

• Positively charged particles that stays in the nucleus of an atom.

• Proton is very small, but it is fairly massive compared to the other particles that make up
matter. The mass of one proton is 1.673 x 10-27 kg.

NEUTRONS

• Particles having no charge.

• Neutrons are about the same size as protons but their mass is slightly greater, 1.675 x 10-27 kg
ATOMIC NUMBER

• Represents the number of electrons or protons of an atom.

ATOMIC MASS

• Represents the sum of protons and neutrons of an atom.

VALENCE ELECTRONS

• Electrons found in the outermost shell or orbit of an atom.

CONDUCTORS

In conductors, electric charges are free to move through the material. In insulators, they are not.

In conductors:

• The charge carriers are called free electrons

• Only negative charges are free to move
• When isolated atoms are combined to form a metal, outer electrons of the atoms do not
remain attached to individual atoms but become free to move throughout the volume of the
material

Other Types of Conductors

Electrolytes

• Both negative and positive charges can move.

Semiconductors

• In-between conductors and insulators in their ability to conduct electricity

• Conductivity can be greatly enhanced by adding small amounts of other elements
• Requires quantum physics to truly understand how they work.

INSULATORS

• Insulators on the other hand are the exact opposite of conductors. They are made of materials,
generally non- metals, that have very few or no “free electrons” float about within their basic
atom structure because the electrons in the outer valence shell are strongly attached by the
positively charge inner nucleus. So if a potential voltage is applied to the material no current
will flow as there are no electrons to move which gives these materials their insulating
properties.
 • Examples of good insulators are marble, p.v.c plastics, rubber, glass ,oil, asphalt, fiberglass,
porcelain, ceramic, dry cotton, dry copper, dry wood, air, diamond, mica, textile fiber, and wax.

• Insulators play an important tool within electrical and electronics because without them
electrical circuit would short together and not work. For example, insulators made of glass or
porcelain are used for insulating and supporting overhead transmission cables while epoxy glass
resin materials are used to make printed circuit boards, PCB’s etc.

SYSTEM’S OF UNITS

SI PREFIXES

Prefix SI Symbol Exponent Form

exa E 1018
peta P 1015
tera T 1012
giga G 109
mega M 106
kilo k 103
deci d 10-1
centi c 10-2
milli m 10-3
micro μ 10-6
nano n 10-9
pico p 10-12
femto f 10-15
atto a 10-18

DIRECT CURRENT SYSTEM

• Direct current (DC) is an electric current that is uni-directional, so the flow of charge is always
in the same direction. As opposed to alternating current, the direction and amperage of direct
currents do not change. It is used in many household electronics and in all devices that
use batteries. Anything that works with a battery works on DC.

ELECTRIC CIRCUIT

• An electric circuit is an interconnection of electrical elements and each component of the

circuit is known as an element.
 • A simple electric circuit in the figure above consists of basic elements such as battery, a light
bulb, connecting wires and a switch.
• An electric circuit is always a closed path. A closed circuit is one that is complete, with good
continuity throughout.

TYPES OF ELECTRIC CIRCUIT

Close Circuit

Open Circuit- implies that the two terminals are points are externally disconnected, which is
equivalent to a resistance R=∞. This means that zero current can flow between the two terminals,
regardless of any voltage difference.

Short Circuit- implies that the two terminals are externally connected with resistance R=0, the same as
an ideal wire. This means there is zero voltage difference for any current value.

ELECTRICAL SYMBOLS

Electrical Symbols are used for components in electrical circuit diagrams.

BASIC ELECTRICAL ENGINEERING INSTRUMENTS

AMMETER

• An ammeter is an instrument used to measure current and must be connected in series with
the circuit.

VOLTMETER

• A voltmeter is an instrument used for measuring electric potential difference between two
points in an electric circuit. and must be connected in parallel with the part of the circuit whose
potential difference is required.

WATTMETER

• A wattmeter is an instrument for the measurement of power in an electrical circuit.

OHMMETER

• An ohmmeter is an instrument for measuring resistance.

MULTIMETER

• A multimeter, or universal instrument, may be used to measure voltage, current and

resistance.

CIRCUIT VARIABLES

1. ELECTRIC CHARGE

Charge is an electrical property of the atomic particles of which matter consists, measured in
Coulombs (C).

Where:
Q = Charge in Coulombs (C)
I = Current in Amperes (A)
t = time in seconds (s)
2. ELECTRIC CURRENT
• Such movement of free electrons creates an electric current
• Materials with large numbers of free electrons are called electrical conductors. They conduct
electrical current.
• rate of flow of electron or electric charge through a conductor or circuit elements
• measured in amperes (A) or

Where:
Q = Charge in Coulombs (C)
I = Current in Amperes (A)
t = time in seconds (s)

3. VOLTAGE

We know that like-charges repel each other whereas unlike charges attract each other. To overcome
this force of attraction or repulsion, a certain amount of work or energy is required. When the charges
are moved, it is said that a potential difference exists and the work or energy per unit charge utilized in
this process is known as voltage or potential difference.

• Also known as electromotive force (emf); electric pressure; potential difference.

• The energy required to move a unit charge through an element, measured in volts (V)

Where:
W = Work (joule)
Q = Charge (coulomb)
4. POWER

Power is the time rate of expending or absorbing energy, measured in watts (W) or . Watt is the
unit of Power.

• Equivalent to one joule of energy consumed in one second

• Name after the British engineer and inventor, James Watt.

Where:
P = electrical power (W)
V = voltage (V)
I = current (A)
R = resistance (Ω)

5. ELECTRICAL ENERGY

Energy is the capacity to do work.

Where:
W = electrical energy (J)
P = electrical power (W)
t = time (s)

Kilowatt-hour (kW-hr)

• Unit in which electrical energy is sold to a consumer.

OHMS LAW

• states that the voltage across a conductor is directly proportional to the current flowing
through it, provided all physical conditions and temperatures remain constant.

Voltage (V)

• Work required to move a unit charge

• Potential difference between two points
• Unit is Volts (V)

Current (I)

• This is the flow of electrical charges

• is a steady flow of electrons
• Unit is Amperes (A)

Resistance (R)

• Resistance is a measure of the opposition to current flow in an electrical circuit.

• Resistance is measured in ohms, symbolized by the Greek letter omega (Ω).
1 calorie = 4.186 joules
1 hp = 746 watts
1 BTU = 252 calories
1 kW-hr = 3600 kJ = 3413 BTU = 860 kcal
1 joule = 1x107 ergs
1 day = 24 hours
1 month = 30 days = 720 hours
1 year = 365 days = 8760 hours

TYPES OF CURRENT

• Direct Current (DC) – is a current that remains constant with time.

• Alternating Current (AC) – is a current that varies sinusoidally with time.

If the current does not change with time, but remains constant, we call it a direct
current (DC).

A time-varying current is represented by the symbol i. A common form of time-

varying current is the sinusoidal current or alternating current (AC).

Conventional current flow: (a) positive current flow, (b) negative current flow
MAIN EFFECTS OF ELECTRIC CURRENT
The three main effects of an electric current are:
(a) magnetic effect
(b) chemical effect
(c) heating effect

Some practical applications of the effects of an electric current include:

Magnetic effect: bells, relays, motors, generators, transformers, telephones, car-ignition and lifting
magnets
Chemical effect: primary and secondary cells and electroplating
Heating effect: cookers, water heaters, electric fires, irons, furnaces, kettles and soldering irons

TYPES OF VOLTAGE
DC Voltage - commonly produce by batteries

AC Voltage - produced by electric generator

A constant voltage is called DC voltage and is represented by V, whereas a sinusoidal time varying
voltage is called an AC voltage represented by v.

CIRCUIT ELEMENTS

There are two types of circuit elements:

1. Active circuit elements – are capable of generating energy such as; generators, batteries,
operational amplifiers and etc. Most important active circuit elements are voltage and current
sources which deliver power to the circuit connected to them. There are two kinds of sources;
Independent sources and Dependent sources
a) Independent Voltage Source – characterized by terminal voltage and completely
independent of the current through it.
b) Independent current source – the current through it is completely independent of
the voltage across it.
c) Dependent or Controlled Source – in which the source quantity is determined by a
voltage or current existing some other location in the electric system under
examination.

2. Passive circuit elements – are not capable of generating energy such as; resistors, capacitors,
inductors and etc.
a) Resistor – The circuit element used to impede the flow of current or, more
specifically, the flow of electric charge is called resistor.
 Resistance – the capacity of resistor to impede the flow of current or, more specifically,
the flow of electric charge is called resistance, expressed by R and measured in ohms
(Ω).

b) Inductor – is a passive element designed to store energy in its magnetic field. It

consists of a coil conducting wire. Inductors may be fixed or variable. The core may be
made on iron, steel, plastic, or air.
c) Capacitors – is a passive element designed to store energy in its electric field. It consists of
two conducting plates separated by an insulator or dielectric. The plate may be aluminum foil
while the dielectric may be air, ceramic, paper or mica.
Capacitance (C) – is the ratio of the charge on one plate of a capacitor to the voltage difference
between the two plates, measured in farads (F)

Two types of capacitors

1. Fixed capacitor
2. Variable capacitor or trimmer capacitor or padder

TYPES OF RESISTORS

• Fixed value resistors – are the type of resistors which offers fixed amount of resistance in the
circuit. A fixed resistor cannot be changed as it is set a specific value.

• Variable Resistors – are the types of resistors in which the value of resistance is not fixed. We
can change the value of resistance in variable resistors.

• Carbon composition Resistor – Carbon composition resistors were used for over 100 years but
are rarely used today. They are large as compared to our general resistors. Carbon composition
resistors are made by mixing carbon granules with the help of binder which is a binding agent
and then converted into a small rod. The biggest advantage of these resistors is that they can
withstand high level of energy pulses. Although they have many disadvantages like big size,
noise, high negative temperature coefficient, and instability. Due to these disadvantages, this
type of resistors are not used today or rarely used. They can be used in RF loads.

• Carbon film Resistor - Carbon film resistors have the carbon film on the ceramic former and
they are covered with insulation coating material like epoxy (for protection). This type of
resistor is not used today as superior resistor technologies are available in lower cost. Carbon
film resistors are formed by cracking of hydrocarbons on a ceramic former which makes carbon
film on it. After that connection are added and a helix cut is given to adjust the value of
 resistance. Helix cut is the smooth curve on the surface; this makes these resistors inductive
and makes them usable in RF applications. The helix curve is indicated as a trimming line. An
electrode cap is connected to the lead wire for closing the carbon film.

• Metal oxide film Resistor - This type of resistor is widely used today. They are far better than
the carbon film resistors. Here, metal oxides (metal film) like tin oxide are deposited on the
ceramic carrier. Then resistance is adjusted by using the trimming line. The resistance varies
depending upon the thickness of deposition and after that by helix curve. After that outer
covering is covered by an epoxy protection layer (insulation coating). These resistors have low
noise and can be supplied to much more close tolerance and thus make them far superior from
carbon film resistors. This type of resistors is used in almost all applications now.

• Wire Wound Resistor - Wire wound resistors are made by winding metal core (wire) on a
ceramic former. The ceramic former is used in costly wire wound resistor. This gives more
resistance than general. After winding wire, they are covered with vitreous or silicon enamel.
The whole material is tightened with electrode cap. This type of resistor is used for high power
applications.

• Variable Resistors - are mainly categorized on the basis of how the resistance value of adjusted.
Here, resistance value depends on the operator or other natural sources. They are mainly
classified as Potentiometer (abbreviated as Pot), Light dependent resistor, thermistors.

Potentiometer
Potentiometers are the type of variable resistors. In potentiometer, there are three terminals
and a rotating shaft which when rotated changes the value of resistance.
LAW OF RESISTANCE

• its varies directly as its length (L)

• its varies inversely as the cross-sectional (A) of the conductor
• it depends on the nature of the material
• it depends on the temperature of the conductor

SPECIFIC RESISTANCE OR RESISTIVITY (Ρ)

• The resistance of electrical materials in terms of unit dimensions length and cross – sectional
area.
• The amount of change of resistance in a material per unit change in temperature.
• The unit is ohm – circular mils per foot

Where:
R = Resistance
A = Cross-sectional area
The resistance is directly proportional to the conductor length.
ρ = Resistivity
The resistance is inversely proportional to the cross – sectional area.
L = Length
V = Volume

Note:
RESISTIVITY OF COMMON ELEMENTS AT 20 °C

Material ρ(Ω-CM/ft.) T°C α at 20 °C

Silver 9.9 243 0.0038
Copper, Annealed 10.37 234.5 0.00393
Aluminum 17 236 0.0039
Tungsten 33 202 0.0045
Zinc 36 250 0.0037

Resistance Resistivity Length Area Volume

Ohm Ohm – m m m2 m3
Ohm Ohm – cm cm cm2 cm3
Ohm Ohm – CM/ft. ft. CM

Circular Mil (CM)

• Area of a circle having a diameter of one mil
• 1 in = 1 000 mils
• 1 MCM = 1 000 CM

Cross – sectional Area

1. Circular Mil (CM)

- Unit of cross-sectional area whose diameter is equal to 1 mil

Where: d = diameter in mil

2. Square Mil
- Unit of cross-sectional area whose sides are equal to 1 mil.

• Area can be in m2 , in2 , ft2 , sq mil, Circular mil

• Note:
1 in = 1 000 mils
CONVERSION BETWEEN CIRCULAR MIL & SQUARE MIL
1 in2 = 10 000 or 106 mils
=
TEMPERATURE RESISTANCE EFFECT
• Rise in temperature – increases the R of pure metals
• Rise in temperature – increases the R of alloys
• Rise in temperature – decreases the R of electrolytes and insulators.

Note:

Where:
R1= initial resistance
R2= final resistance
T = inferred absolute temperature
t1 = initial temperature
t2 = final resistance
α = temperature coefficient of resistance
ΔT = t2 – t1

INFERRED ABSOLUTE TEMPERATURE (T) in °C

COPPER ANNEALED = 234.5

SILVER = 243
ALUMINUM = 236
HDC (HARD DRAWN COPPER) = 242

TEMPERATURE COEFFICIENT OF RESISTANCE (@20 °C)

COPPER = 0.00393/°C
SILVER = 0.0038/°C
ALUMINUM = 0.0039/°C

Using Similar Triangles,

Resistance vs. Temperature

CONDUCTORS UNDERGOING DRAWING PROCESS (Constant Volume, Same Material)

• In the process, the waste of the material is assumed negligible (efficiency is 100%), thus keeping the
volume to be constant all throughout the process.

RESISTOR COLOR CODING

Resistor Color Code

• Manufacturers typically use a color band system known as the resister color code.

COLOR DIGIT MULTIPLIER TOLERANCE

BLACK 0 1
BROWN 1 101
RED 2 102
ORANGE 3 103
YELLOW 4 104
GREEN 5 105
BLUE 6 106
VIOLET 7 107
GRAY 8 108
WHITE 9 109
GOLD 10-1 ±5%
SILVER 10-2 ±10%
NO COLOR ±20%

TOLERANCE

• Tolerance is the amount (in percent) by which the actual ohmic resistance can be different from the color
coded value
CONDUCTANCE (G)

• Conductance is a measure of the material’s ability to conduct current.

• Reciprocal of Resistance
• Measured in mho (℧), Siemens (S)

SIEMENS (formerly mho)

• Unit of conductance
• Named after the german engineer, Earnst Werner von Siemens (1816 -1892)

Conductivity (δ)

• reciprocal of resistivity