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TCOM 308
Basics of Electronics
Electronics
• Electronics is the study of Electrons
• The word “electricity” is derived from the
Greek word “elektron” which means “amber”
• Probably because rubbing amber on cloth
created a static electrical charge
Electrons
• One of three types of subatomic particles
– Protons (+) are positively charged particles in the
nucleus of an atom
– Neutrons (0) are non-charged or neutral particles
in the nucleus of an atom
– Electrons (-) are negatively charged particles in
orbit around the nucleus of an atom
• Electrons are held in orbit by the oppositely
charged protons
Electrons
Electrons
Whirling in orbit around nucleus
Conductors
• Some substances contain an excess of
electrons compared to the number of protons
• Excess electrons are known as “free electrons”
• Substances with an abundance of free
electrons are known as conductors
• Conductors allow free electrons to easily be
dislodged
Conductors
• The best conductors are metals, which
naturally contain excess free electrons
• The best conductor is silver – but expensive
• Gold is an excellent conductor – but also
expensive
• Other good conductors include copper,
aluminum, steel, brass, bronze, etc.
Conductors
Representation of number of free electrons in three substances
Insulators
• Substances with a shortage of electrons are
called insulators
• Electrons are difficult to dislodge from their
orbits and resist flowing
• Non-conductors include glass, rubber,
fiberglass, porcelain, ceramic, plastic, air,
diamond
Current flow
• Electron flow through a conductor is called
(electrical) current
• Particles with the same electrical charge repel
one another
• Particles with opposite electrical charges
attract one another
• Since electrons are negative, current flows
from the negative to the positive
Current flow
Electrons move from one atom to the next,
where more electrons are dislodged, and those
electrons flow to the next atom, and so on
Current flow
• To start current flowing, some “force” or
“pressure” is require to push the electrons out
of their orbits
• This force is called electro-motive force or emf
• EMF is referred to as a “potential”
• EMF may thought of as a negative charge that
will push the first electrons out of orbit and
start current flowing through a circuit
• EMF is measured in volts
Current flow
• The “volume” or quantity of electrons moving
is referred to as the amount of current flow
• The amount of current flow is the amount of
electricity flowing
• Current flow is measured in amperes or amps
Current flow
• For current to flow then we need:
– A source of emf
– A conductor
– A circuit
• Circuit is a closed path or “circle”
– The circuit ends where it began
Circuit
Circuit
Schematic symbols used in electronics
Incandescent lamp
_
+
Battery
Circuit
• Circuit is composed of
– a source or multiple sources of emf
– a lode or the wire, devices, etc. through which the
current flows
Direct current
• Batteries supply emf to move electrons in one
direction
• When electron movement is one direction
only, the current is known as direct current or
DC
• Electrons are always moving toward the
positive post of the battery
Alternating current
• Generators can supply emf to move electrons
in two directions – vibrating back & forth
• When electrons move in two directions, the
current is known as alternating current or AC
• Electrons move back and forth between atoms
Resistance
• Because electrons do have mass, and because
they are held in orbit by their electrical
charges, they are reluctant to leave orbit
• This reluctance is called resistance
• Resistance is measured in ohms (Ω)
Resistance
• Factors affecting resistance:
– Length of conductor
– Cross-sectional area of conductor
– Temperature of conductor
– Composition of conductor or material
Ohm’s law
• Three variables in the circuit:
– EMF is measured in volts and expressed by the
symbol E
– Current flow is measured in amperes and
expressed by the symbol I
– Resistance to current flow is measure in ohms and
expressed by the symbol R
• If we know any two variables we can calculate
the third using a formula known as Ohm’s law
Ohm’s law
• Resistance X Current = Voltage (E=R X I)
• Voltage ÷ Current = Resistance (R=E ÷ I)
• Voltage ÷ Resistance = Current (I=E ÷ R)
Ohm’s law
E
I R