Circuits 1 – Module 2A
ELEL31E
Prepared by:
Engr. Ronaldo Amos
Circuits 1 – Module 2A
► Definition
of Electricity
► SI System of Measurement
► Electric charge
► Structure of matter
► Electrical classification of materials
► Electric field and electric force
► Electric potential
► Electric current, direction of flow
► Material resistance
Fundamentals of Electricity
Electricity
►
Is an electric charge, or an electrical energy or
electromagnetic energy
 Static electricity
 Moving electric current
Phenomenon associated with the presence and motion of
electrons and other charged particles
► The physical phenomena arising from the behavior of
electrons and protons that is caused by the attraction of
particles with opposite charges and the repulsion of
particles with the same charge.
► The flow of electrons and protons in a closed circuit due to
electric charge.
► When a potential difference between two charges forces a
third charge to move, the charge in motion is called and
electric current.
► The flow of electric current in a closed circuit
►
► SI
system of measurement
 SI stands for International System of Units
 At present, two major systems—the English (US
Customary) and the metric—are in everyday use.
► Examples
of metric: meter, kg, ampere, joule, hertz, ohm
► Examples of English: inch, pound, ft, horsepower, ft-lb
 The SI system combines the MKS metric units and the
electrical units into one unified system
 Though the use of SI system is very wide, there are
instances where expressing it in English system is more
practical. For example, the HP as a unit of power is
preferred over W when it comes to very large
quantities. Thus, it is necessary to know the conversion
of these units from SI to English and vise-versa.
► Unit
Conversion
 Example: convert 12 cm to inches
 12cm x 1in/2.54cm = 4.72 in
Unit Prefixes
Kilo = K = 103
Mega = M = 106
► Giga = G = 109
► Tera = T = 1012
► Milli = m = 10-3
► Micro = µ = 10-6
► Nano = n = 10-9
► Pico = p = 10-12
 Usually resistances are expressed in , K , M , and G
.
 Amperes are usually expressed in A, mA, and µA.
 Voltages in electronics are usually expressed in V, mV, and
µV. In electrical, voltages may go up to several KV,
and MV.
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Conversion of Unit
Sample Problem:
► Electric
charge (Q)
 Is a fundamental property of matter and is influenced
by elementary particles such as electrons and protons
 A body is said to be charged, if it has an excess or
deficit of electrons from its normal values due to
sharing.
 The quantity of electron flow or charge
►2
kinds of charges according to Benjamin Franklin (US scientist:
1706 – 1790)
 Positive charge (carried by protons)
 Negative change (carried by electrons)
 Unit: Coulomb Symbol: C
► Named
after the French physicist, Charles Augustin de Coulomb
(1736 – 1806)
► 1 coulomb = 6.242 x 1018 electrons
► Electron charge = 1/6.242 x 1018 = 1.602 x 10-19 C
 Like poles repel, unlike poles attract. Like charges repel,
unlike charges attract.
►
Structure of Matter
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The elementary particles are basic form of matter,
and as they combine they form another matter,
the atom; and as atoms combine forms yet another different matter
Matter – is anything in the universe that has mass, occupies space, and is
convertible to energy.
Compound – a combination of two or more different atoms or elements.
Element – substance consisting of atoms of only one kind. This is
considered as the elementary (irreducible) chemical identity of materials
which means that it cannot be decomposed any further by chemical action.
Molecule – the smallest particle that a compound can be reduced before
it breaks down into its elements. It’s the smallest part of a compound or
material that retains all the properties of the compound.
Atom – smallest part of that an element can be reduced to and still
keeping the properties of the element.
Atomic number – represents the number of protons in the nucleus of an
atom, which in a neutral atom equals the number of electrons outside the
nucleus.
Atomic mass – mass of the atom, which represents the sum of protons
and neutrons. Electrons has a relatively very small mass and therefore
neglected.
Valence electrons – electrons found in the outermost shell or orbit of an
atom
Bohr Atomic Model
Electron charge = -1.602 x 10-19 C
Proton charge = +1.602 x 10-19 C
Neutron = 0 C
Joseph John Thomson (1856 – 1940)
A British physicist who discovered
the electron in 1897, which he
initially called corpuscles, meaning a
living cell.
• Electric current – the directional motion of
electrons
• Electrostatics – deals with stationary
charged particles
• Magnetism – effects of moving electrons
• Electromagnetism – magnetism due to
electric current.
► Bohr
Atomic Model
 Niels Henrik David Bohr (1885 – 1962)
► Danish
physicist who in 1913 developed a new model of atomic
structure call the Bohr Atomic Model.
 In this model, electrons travel in defined circular orbits
around the nucleus. The orbits are labeled by an
integer, the quantum number n.
 Electrons can jump from one orbit to another by
emitting or absorbing energy.
 The maximum number of electrons (Ne) that can
occupy a given shell or the nth shell can be
approximated by:
► Ne
= 2n2 where n is the nth shell
► Example: Cu 29 electrons
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1st shell, n=1; Ne = 2 electrons
2nd shell, n=2 ; Ne = 8 electrons
3rd shell, n= 3; Ne = 18 electrons
4th shell, Ne = 1 valence electron = 29 – 28
Note: the farther the electron from the nucleus, the higher is its
energy level
► Mass
of
 Electron = 9.109 x 10-13 kg
 Proton = 1.673 x 10-27 kg
 Neutron = 1.673 x 10-27 kg
► Charge
to mass ratio (C/kg)
 Electron = 1.76 x 1011
 Proton = 3.58 x 107
► Valence
shell – is the outer most shell or the last
shell.
► Free electrons – are originally valence electrons.
As they gain enough energy they escape from the
valence shell and become free
 Free electrons do not remain permanently associated
with the atoms of a solid, they move from one atom to
another and during conduction of electricity, it is these
free electrons that will be in motion.
Coulomb’s Law
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The force between charges was studied by the French scientist Charles
Coulomb (1736–1806).
Coulomb determined experimentally that the force between two
charges Q1 and Q2 (Figure 2–5) is directly proportional to the product
of their charges and inversely proportional to the square of the
distance between them.
•
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•
where Q1 and Q2 are the charges in coulombs,
r is the center-to-center spacing between them in meters,
and
k = 9 x 109.
Element #of e #of p #of neu #val e
copper
29
29
34
1
aluminum
13
13
14
3
germanium
32
32
41
4
Electrical Classifications of Material:
• the number of valence electrons is a common indication that tells us the
electrical characteristics of a material.
•Conductor –
material with less than four valence electrons. Conductors
allow electrical current to flow easily because they have more free electrons.
•Insulator –
material with more than four valence electrons. Insulators
will not allow electrical current to flow easily because they have few or even
no free electrons.
•Semiconductor –
with exactly four valence electrons. Semiconductors
have electrical characteristics in between conductors and insulators.
► Energy
bands
 Before a valence electron can escape from its shell and
becomes free, it must gain energy of at least equal to
the energy gap
► Energy
gap – the energy difference between the valence band
and conduction band. Its unit is the electron volt (eV)
 1eV = 1.6 x 10-19 Joule
► A unit of energy equal to the energy gained by an electron in
passing from a point of low potential to a point one volt
higher in potential.
► Valence
band – the region where the valence shell and valence
electrons are occupying. It is the highest energy level before
conduction band.
► Conduction band – the region where free electrons are said to
be present . Electrons a this band have a higher energy level
than those electrons at the valence band.
► Forbidden band – the region in an atom where no electrons
exist. It is in between two allowed bands, such as between
valence and conduction bands.
Energy Band Diagram of an Atom
Highest
energy level
Conduction band
Increasing energy level
Forbidden Band
Valence band
1st energy level
Valence shell
level
Levels bet.1st
energy level &
valence band
Forbidden Band
Nucleus Ground State
Energy gap (Eg) of :
Conductors = 0 eV
Insulators > 5 eV
Semiconductors = 1eV
Energy gap (Eg)
1st shell closest to
the nucleus
electrons
Eg = 0 means that the valence electrons can easily
become free. This explains why conductors have the
most number of free electrons and can easily support
electric current flow.
►
Law of Conservation of Charge:
 The net charge of an isolated system remains constant. The only
way to change the net charge of a system is to bring in charge
from elsewhere, or remove charge from the system.
►
Law of Conservation of Charge-Energy:
 Electric charge is neither created nor destroyed but is transferred
from one body to another.
Ion – a charged body
► Anion – negatively charged ion
► Cation – positively charged ion
► Electropositive elements are elements that give up
electrons in chemical reactions to produce positive ions.
These elements are metallic in nature.
► Electronegative elements are elements that accept
electrons in chemical reactions to produce negative ions.
These elements are nonmetallic in nature.
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Electric Field and Electric Force
 When the body is electrically charged, it is said to have electric field
in its surroundings. This field interacts with other charged bodies
and will produce an electric force that may cause them to move.
 Electric field – is the area or region surrounding an electrically charged
particle or body
 Electric force – the force produced due to the electric field of a
charged particle or body.
► Electric
potential
 the ability of a charged body to do work on charged particles such as
electrons
 Electric potential difference – the difference between the
capacities (potentials) of two charges to do work.
 Volt (V) – the unit of potential difference. A potential of one volt (1V)
has the capacity to do one joule (1J) of work in moving one coulomb (1C)
of charge. Named after the Italian physicist, Alessandro Volta (1745-1827)
 V = W/Q where: w = work or energy in joules
Q = charge in coulombs
 Voltage – another name for potential difference.
 Electromotive force (emf) – the electrical force that moves the
charged p;articles such as electrons (electron moving force). The term emf
is used interchangeably with potential difference and voltage.
►
Electric current
 Any directional movement of electric charges such as electrons.
 Current in gases and liquids – generally consist of flow of positive ions in
one direction together with a flow o f negative ions in the opposite
direction.
 Current in solids – such as wires, consist of the flow of electrons, and is a
measure of the quantity of charge passing any point of the wire per unit of
time.
►
I = dQ/ dt
C/s or Ampere, the intensity of electron flow
 Ampere (A) – the unit of electric current. Named in honor to the French
physicist and mathematician, Andre M. Ampere (1775 – 1836)
 Current density (J) – the current per unit cross-sectional area
►
J = I/A = ampere/m2
 Closed Circuit – a path for current flow
 Open circuit – a path for current flow is cut or opened.
 Short circuit – a path for current flow that bypasses a component or subcircuit, which may create an overload.
 Schematic diagram – a diagram that uses symbols for components to draw
the circuits
 Pictorial diagram – a diagram using pictures of component to show the
circuits.
 Direct current – charges flow in one direction only
 Alternating current – the motion of electric charges is periodically reversed.
 Conventional current flow – the flow of charge from positive to negative.
 Electron flow – the flow of charge from negative to positive.
A guide to solving problems
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Determine what is given in the problem, that is, the given scenario or
situation. The schematic diagram is usually given for you to draw and identify
the known and the unknown in the diagram.
Determine what is being asked by the problem, that is, identify the problem
Determine the theories, principles, formulas related to the problem and the
given scenarios or situation
From the formulas that relates the known and the unknown, substitute the
given values.
Write your solutions at the point of view of the reader, which means that it
must be on a step-by-step process avoiding short cuts that may lead to
misunderstanding by the reader.
Write legibly, logically, and highlight your final answer.
Example:
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Given:
Find ?
Formula
Solution
Answer inside a box
In your computations, the resolution or number of decimal places of your
computed numbers should be at least 2 decimal places more than the highest
resolution number in the given data when not exact.
► The final answer should have 1 decimal place more than the highest resolution
number in the given data when not exact.
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Sample Problems:
1.
A positively charged dielectric has a charge of 2 coulombs. If
12.5 x 1018 free electrons are added to it, what will be the net
charge on the said dielectric?
Q1= +2C
Q2= -12.5 * 1018e * (1C/6.25 * 1018e) = -2C
Qnet= Q1+Q2 = 2 + (-2)
2.
3.
Qnet= 0
A battery can deliver 10 joules of energy to move 5 coulombs of
charge. What is the potential difference between the terminals of
the battery?
Note: volt = joules per coulomb
E = W/Q = 10/5
E = 2 volts
A cloud of 2.5 x 1019 electrons move past a given point every 2
seconds. How much is the intensity of the electron flow?
Note: ampere = coulombs per second
Q = (2.5 * 1019) * 1C/(6.25 * 1018) = 4C
I = Q/t = 4/2
I = 2 amperes
Sample Problems
4.
The current in an electric lamp is 5 amperes.
What quantity of electricity flows towards the
filament in 6 minutes?
Q = It = 5(6min * (60sec/1min))
Q = 1800 C
5.
A consistent current of 4 A charges a capacitor.
How long will it take to accumulate a total
charge of 9 coulombs on the plates?
t = Q/I = 8/4
t = 2 sec
Exercises:
1.
2.
Perform the following conversions:
a.
b.
c.
d.
e.
f.
27 minutes to seconds
0.8 hours to seconds
2 h 3 min 47 s to s
35 horsepower to watts
1827 W to hp
23 revolutions to degrees
a.
b.
c.
d.
e.
f.
156 mV to volts
0.15 mV to microvolts
47 kW to watts
0.057 MW to kilowatts
3.5104 volts to kilovolts
0.0000357 amps to microamps
Convert the following:
3
4. Positive charges Q1 2 mC and Q2 12 mC are separated center to center by 10
mm. Compute the force between them. Is it attractive or repulsive?
5. Two equal charges are separated by 1 cm. If the force of repulsion between
them is 9.7 102 N, what is their charge? What may the charges be, both
positive, both negative, or one positive and one negative?
6. After 10.61 1013 electrons are added to a metal plate, it has a negative charge
of 3 mC. What was its initial charge in coulombs?
Homework
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Homework
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Special Assignment
►
Research & Report Different Sources of Electricity (deadline
- next week)
 Report on AC sources
 Report on DC sources
 Content:
► Source
of Electricity – Description
► How it generates electricity?
 Equipment/ parts/ composition involve, etc.
 Energy conversion to electrical energy – process
► Control
of electricity
 Transmission and Distribution
 Safety, Length of Life, etc.
►
Research & Report about Superconductors (deadline – next
week)