# DC1-1 VOLTAGE

```DC1-1 VOLTAGE
CIRC-1005 DC Circuits
Department of Electrical Engineering Technology, RRC Polytech
&copy; 2022 RRC Polytech
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DC1-1 VOLTAGE
Dr. Norman Huang
Instructor of EET
BSEng, MSEng, PhDEng
Based on the Slides made by Preet Dhingra
Electrical circuits are everywhere in this technologically
lights, TVs, computers, cars, cell phones, air conditioning, you
name it: life would be totally different if we didn't have
circuits.
But what exactly is a circuit?
What is an Electric Circuit?
An electrical circuit is an interconnection of various
electrical circuit elements like an electrical energy source, a
load, a switch and conducting wires.
But What is Electricity?
Electricity is a form of energy. To understand this, you need to
know about atoms and the structure of atoms.
Voltage and Current
The term voltage is encountered practically everyday. We have all
replaced batteries in our flashlights, answering machines,
calculators, automobiles and so on, that had specific voltage
ratings.
The most outlets in our homes are 120 volts.
Voltage and Current
Although current may be a less familiar term, we know
what happened when we place too many appliances
on the same outlet- the circuit breaker opens due to the
excessive current.
Atomic Theory Review:
• All elements are arranged in the periodic table
according to their atomic number.
• An atom consists of a nucleus with electrons
orbiting around it.
• Atom has equal number of protons in the
nucleus which is the same as the number of
electrons.
Atomic Theory Review:
• Protons, have a positive electrical charge. Neutrons have
no electrical charge while electrons, have a negative
electrical charge.
• Neutrons and protons exist inside the nucleus making it
positively charged whereas the electrons revolve around
the nucleus in orbitals. The outermost shells are called
valence shells and electrons revolving in it are called
valence electrons.
Atomic Theory Review:
• An electron has a charge equal to approximately 1.602 x 10-19 Coulombs.
• A proton has a charge equal to approximately
+1.602 x 10-19 Coulombs
Atomic Theory Review:
• The coulomb (C) is
the SI unit of electric
charge.
Hydrogen and Helium atoms
Copper:
Is the most commonly used
metal in the electrical
/electronics industry.
It has 29 electrons in orbits
around the nucleus, with the
29th electron appearing all by
itself in the 4th shell.
Copper:
• If 29th electrons gain sufficient energy from the
surrounding medium to leave the parent atom, it is
called a free electron.
• In 1 cubic in. of copper at room temperature, there
are approximate 1.4 &times; 1024
Electrical Charge:
• Electrical Charge is an intrinsic property of matter that
manifests itself in the form of forces – electrons repel other
electrons but attract protons, while protons repel each other
but attract electrons.
Electrical Charge:
• Example: Consider an atom has equal numbers of electrons
and protons, and since their charges are equal and opposite
they cancel, leaving the atom as a whole uncharged.
• However, if the atom acquires additional electrons (leaving it
with more electrons than protons), we say that it (the atom)
is negatively charged; conversely , if it loses electrons and is
left with fewer electrons than protons, we say that it is
positively charged.
Electrical Charge:
• The term “charge” in this sense denotes an imbalance
between the number of electrons and protons present in the
atom.
• The term “charge” is denoted by the letter Q, and its unit of
measurement in the SI system is Coulomb.
One coulomb of charge = 6.242 x1018 electrons.
Coulomb’s Law:
According to Coulomb’s law, force between charges is directly
proportional to the product of their charges and inversely
proportional to the square of the distance between them.
𝑄1 𝑄2
𝐹=𝑘 2
𝑟
where F = Force (Newton), k = constant, Q1and Q2 are the
charges in coulombs and r is the distance between the two
charges in meters.
Voltage:
• When charges are detached from one body and transferred
to another, a potential difference or voltage results between
them.
• In general, every source of voltage is established by simply
creating a separation of positive and negative charges.
Definition of Voltage: the Volt
• In electrical terms, a difference in potential energy is
defined as voltage.
• In general, the amount of energy required to separate
charges depends on the voltage developed and the
amount of charge moved.
Definition of Voltage: the Volt
• By definition, if a total of 1 joule (J) of energy is used
to move the negative charge of 1 coulomb (C), there is
a difference of 1 volt (V) between the two points.
• In equation form:
𝑊
𝑉=
𝑄
𝑉𝑜𝑙𝑡𝑠, 𝑉
• Where W is the energy in joules, Q is the charge in
Coulombs and V is the voltage in Volts.
𝑉=
1
= 1V
1
1
Note carefully that voltage is defined
between points.
• For the case of the battery, for example, voltage appears
between its terminals.
• Thus, voltage does not exist at a point by itself, it is always
determined with respect to some other point.
• The difference in voltage between any two points, connections or
junctions (called nodes) in a circuit is known as the Potential
Difference, commonly called the Voltage Drop.
• The Potential difference between two points is measured
in Volts with the circuit symbol V
• A constant voltage source is called a DC Voltage and a voltage that
varies periodically with time is called an AC voltage.
Electrical Voltage
• Voltage, ( V ) is the potential energy between two points on a
circuit. One point has more charge than another. This
difference in charge between the two points is called voltage.
Water = Charge
Pressure = Voltage
• Voltage between two points is one Volt if it require one Joule
of work to move one Coulomb of charge from one point to
another in a conducting material.
DC Voltage Source:
Batteries: a) Primary (non-rechargeable)
b) Secondary (chargeable)
Primary Cells:
a) Alkaline (1.5V nominal Voltage)
b) Lithium (3V nominal voltage, good for low temp.)
Secondary Cells:
b) Nickel Metal Hydride
DC Voltage Source:
Solar Cells
Other DC Sources:
a) Generators
b) Power Supplies (in labs)
c) Fuel Cells
Slide 28
Reference
• Some figures and animations and Table are cited from
• Boylestad, R. L., Introductory Circuit Analysis, Pearson, 13th Edition
Thank you!
See you next time!
```