The Electron Theory of Electrification
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Matter- anything that occupies space and has mass
Element - a substance that cannot be decomposed
any further by chemical action
Compound - a combination of two or more elements
Molecule - smallest particle that a compound can be
reduced to before it breaks down into element
Atom
- smallest part that element can be reduced
to and still keeping the properties of the element
Mixture - it is a material composed of two or more
substances, each of which retains its own
characteristic properties
Proton
- positively charge particle
- having a mass of 1.67x10-27 kg
Neutron
- no charge particle(neutral)
Courtesy: PLTW
Electron
- negatively charge particle
- having a mass of 9.11x10-31kg
- having a charge of -1.602x10-27C
The Electron Theory of Electrification
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Mass of proton is 1840 times the mass of electron.
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Normally, the atoms are electrically neutral, that
the number of electrons and protons are the
same.
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Like electrical charges repel and unlike charges
attract to each other
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Earth is more negative and atmosphere is more
positive
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When an electron is removed from a neutral
atom, this atom becomes positively charge and is
called ‘positive ion’. If an electron is added to a
neutral atom, it becomes negatively charged and
is called ‘negative ion’.
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Ion –gain or loss of an atom
Courtesy: PLTW
The Electron Theory of Electrification
Valence electrons – electrons found in the
outermost shell or orbit of an atom
How to get the number of valence
electrons?
N= 2𝑛2
where, N is the number of electron in
a given shell n
The Electron Theory of Electrification
CLASSIFICATION OF MATERIALS ACCORDING TO CONDUCTIVITY
Conductor
Has 3 or less number of valence electrons
Easy to dislodge from the orbit
Semi-conductors
Has exactly 4 valence electrons
By adding impurity (doping process) it will become a good conductor or good insulator
Insulator
Has 5 or more valence electrons
Needs enough energy to dislodge from the orbit
Courtesy: PLTW
The Electron Theory of Electrification
CLASSIFICATION OF MATERIALS ACCORDING TO CONDUCTIVITY
Conductor
Has 3 or less number of valence electrons
Easy to dislodge from the orbit
Semi-conductors
Has exactly 4 valence electrons
By adding impurity (doping process) it will become a good conductor or good insulator
Insulator
Has 5 or more valence electrons
Needs enough energy to dislodge from the orbit
Courtesy: PLTW
The Electron Theory of Electrification
CLASSIFICATION OF MATERIALS ACCORDING TO CONDUCTIVITY
Conductor
Has 3 or less number of valence electrons
Easy to dislodge from the orbit
Semi-conductors
Has exactly 4 valence electrons
By adding impurity (doping process) it will become a good conductor or good insulator
Insulator
Has 5 or more valence electrons
Needs enough energy to dislodge from the orbit
Courtesy: PLTW
Part of the nucleus of an atom is made up of protons. Each
proton has a positive electrical charge and attracts electrons;
neutrons form the remainder of the nucleus. Neutrons are
electrically neutral. They can neither attract nor repel other
electrical charges
Name
Charge
Mass (kg)
Proton
Positive Charge
1.672 𝑥 10−27
Electron
Negative Charge
9.107 𝑥 10−31
Neutron
No charge
1.672 𝑥 10−27
Element
No. of electrons
No. of Protons
Number of Neutrons
Valence Electrons
Copper
29
29
34
1
Aluminum
13
13
14
3
Germanium
32
32
41
4
One or more electrons revolve continuously around the
nucleus of an atom (just as the planets revolve about the sun).
Electrons possess a negative electrical charge and are very
much lighter in weight than protons. All electrons are alike
regardless of the atoms of which they are a part. An atom
contains the same number of electrons as protons. For
example, the aluminum atom has thirteen electrons and
thirteen protons.
An electric circuit contains a closed path for
providing a flow of electrons from a voltage
source or current source. The elements
present in an electric circuit will be in series
connection, parallel connection, or in any
combination of series and parallel
connections.
BASIC PARTS OF A CIRCUIT:
1.SOURCE
An electric circuit contains a closed path for
2.WIRES/CONDUCTORS
providing a flow of electrons from a voltage
3.LOAD
source or current source. The elements
present in an electric circuit will be in series
4.SWITCH
connection, parallel connection, or in any
combination of series and parallel
connections.
All DC sources of electrical pressure
have two terminals to which electrical
devices are connected. These terminals
have electrical polarity. One terminal is
the positive terminal, whereas the other
is the negative terminal.
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𝟔. 𝟐𝟓 𝒙 𝟏𝟎𝟏𝟖 𝒆𝒍𝒆𝒄𝒕𝒓𝒐𝒏𝒔 𝒐𝒓 𝒑𝒓𝒐𝒕𝒐𝒏𝒔
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Charge of each electron/proton: 𝟏. 𝟓𝟗𝒙𝟏𝟎−𝟏𝟗 𝑪
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one coulomb is measured each second for a wire carrying a current of 1
ampere
Q - symbol for charge that does not vary with time (e.g., battery)
q(t) – instantaneous amount of charge or charge that varies with
time
𝑸 = 𝑰𝒕
𝑄 = 𝑡𝑜𝑡𝑎𝑙 𝑐ℎ𝑎𝑟𝑔𝑒 𝑚𝑜𝑣𝑖𝑛𝑔, 𝑖𝑛 𝑐𝑜𝑢𝑙𝑜𝑚𝑏𝑠 𝐶
𝐼 = 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝑓𝑙𝑜𝑤, 𝑖𝑛 𝑎𝑚𝑝𝑒𝑟𝑒𝑠 (𝐴)
𝑡 = 𝑡𝑖𝑚𝑒 𝑜𝑓 𝑜𝑐𝑐𝑢𝑟𝑒𝑛𝑐𝑒, 𝑖𝑛 𝑠𝑒𝑐𝑜𝑛𝑑𝑠 (𝑠)
Symbol convention throughout the course:
Upper case
- time-invariant quantities
- e.g., Q, I, E, V, P
Italics lower case
- time varying quantities
- more generic
- e.g., q, i, e, v, p
𝑸
𝑰=
𝒕
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𝐼 = 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝑓𝑙𝑜𝑤, 𝑖𝑛 𝑎𝑚𝑝𝑒𝑟𝑒𝑠 (𝐴)
𝑄 = 𝑡𝑜𝑡𝑎𝑙 𝑐ℎ𝑎𝑟𝑔𝑒 𝑚𝑜𝑣𝑖𝑛𝑔, 𝑖𝑛 𝑐𝑜𝑢𝑙𝑜𝑚𝑏𝑠 𝐶
𝑡 = 𝑡𝑖𝑚𝑒 𝑜𝑓 𝑜𝑐𝑐𝑢𝑟𝑒𝑛𝑐𝑒, 𝑖𝑛 𝑠𝑒𝑐𝑜𝑛𝑑𝑠 (𝑠)
𝑑𝑞
𝑖 = 𝑑𝑡
Current Types
• Direct current (DC) is the movement of electrons in one
direction in a conductor.
• Pulsating direct current is a current in one direction that
varies in intensity at a regular interval of time.
• Alternating current (AC) is a current that changes in
direction and intensity at a regular interval of time.
𝑾
𝑬=
𝑸
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𝐸 = 𝐸𝑀𝐹 𝑜𝑟 𝑣𝑜𝑙𝑡𝑎𝑔𝑒 𝑜𝑟 𝑝𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒, 𝑖𝑛 𝑣𝑜𝑙𝑡𝑠 (𝑉)
𝑊 = 𝑒𝑛𝑒𝑟𝑔𝑦 , 𝑖𝑛 𝐽𝑜𝑢𝑙𝑒𝑠 (𝐽)
Q = 𝑐ℎ𝑎𝑟𝑔𝑒, 𝑖𝑛 𝑐𝑜𝑢𝑙𝑜𝑚𝑏𝑠 (𝐶)
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When an emf is applied to the ends of a conductor, it is proper to refer to the
existence of a potential difference between such ends; also since increments of
emfs are required for successive increments of conductor, it is customary to regard
a potential difference as a drop in potential along the length of the conductor
By definition,
𝑑𝑤
𝑣=
𝑑𝑞
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Ω
𝑷 = 𝑬𝑰
𝑾 = 𝑷𝒕
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𝑊 = 𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐 𝑒𝑛𝑒𝑟𝑔𝑦, 𝑖𝑛 𝑗𝑜𝑢𝑙𝑒𝑠 𝐽
𝑃 = 𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐 𝑝𝑜𝑤𝑒𝑟, 𝑖𝑛 𝑤𝑎𝑡𝑡𝑠 𝑊
𝐼 = 𝑐𝑢𝑟𝑟𝑒𝑛𝑡, 𝑖𝑛 𝑎𝑚𝑝𝑒𝑟𝑒𝑠 𝐴 ,
𝐸 = 𝑒𝑚𝑓 𝑜𝑟 𝑣𝑜𝑙𝑡𝑎𝑔𝑒, 𝑖𝑛 𝑉
𝑡 = 𝑡𝑖𝑚𝑒, 𝑖𝑛 𝑠𝑒𝑐𝑜𝑛𝑑𝑠 (𝑠)
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Power is the capacity to do work. It is also
defined as energy per unit time.
Why power and energy calculation is important?
1. Although voltage and current are useful variables in the analysis and design of electrically
based systems, the useful output of the system often is nonelectrical, and this output is
conveniently expressed in terms of power or energy.
2. All practical devices have limitations on the amount of power that they can handle. Voltage
and current calculations by themselves are not sufficient in the design process.
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If a current of 2A flows through a point
in a wire for 30 seconds, how many
coulombs pass through the point in the
wire?
What quantity of charge must be
delivered by a battery with a potential
difference of 100 V to do 500 J of work?
A radio receiver draws 0.9 A at 110 V. If
the set is used 3 hours per day, how
much energy does it consume in 10
days?
Sample Problem: An automobile battery is charge with a constant current of 2A for five
hours. The terminal voltage of the battery is 𝑣 = 11 + 0.5𝑡 𝑓𝑜𝑟 𝑡 > 0, where t is in hours. (a)
Find the energy delivered to the battery during the five hours. (b) If electric energy costs 15
cents/kWh, find the cost of charging the battery for five hours.
(1.84 cents)
Units
International System of Units or Systeme International (SI)
– the standard system of units adopted by the National Bureau of Standards in 1964
The seven Base Units of SI
Courtesy: Hayt et al.
Other Standard units in electric circuits:
Joule for work or energy
Watt for power
Other units of work/energy and power?
SI Prefixes
Active Elements deliver power to other elements,
which are present in an electric circuit. Sometimes,
they may absorb the power like passive elements.
That means active elements have the capability of
both delivering and absorbing power.
Passive Elements can’t deliver power (energy) to other
elements, however they can absorb power. That
means these elements either dissipate power in the
form of heat or store energy in the form of either
magnetic field or electric field.
Examples: Voltage sources and current sources.
Examples: Resistors, Inductors, and capacitors
Exercise: The current in a conductor changes uniformly from zero to 2 amp in 3 seconds,
remains steady at 2 amp for 6 seconds, and then drops uniformly to 1.5 amp in 8 seconds.
Calculate the total amount of charge transferred in the time of 17 seconds.