Fundamentals of Electricity
Franklin County Amateur Radio Club
Technician Class License Course
Class 3 – Fundamentals of Electricity
Bob Solosko W1SRB
Fundamentals of Electricity
Electrons
• All materials are made up of atoms
• Atoms are composed of protons, neutrons
and electrons
• electrons have a positive charge
• protons have a negative charge
Protons
And
Neutorns
• In some materials, electrons are held tightly
to the atom
• these materials are insulators
• examples:
• wood, ceramics, plastics
• In some materials, electrons are held loosely
to the atom are free to move around
• these materials are conductors
• examples:
• copper, silver, aluminum
Electricity is about how electrons flows through materials
Fundamentals of Electricity
Controlling the flow of electrons is the
foundation for the operation of
– Radios
– Ipods
– Computers
– Telephones
– Recorders
– Stereos
– House lights
Fundamentals of Electricity
• There are three characteristics to electricity:
– Electromotive Force
– Current
– Resistance
• All three must be present for electrons to flow
Fundamentals of Electricity
Electromotive Force (EMF or E)
– “electro”: electrons
– “motive”: movement
– “force”: the push
• Electromotive force is the push that causes
electrons to move through a conductor
• Measured in volts
• Usually referred to as voltage
Fundamentals of Electricity
Current (I)
• Current is the amount of electrons that flow
through a conductor over time
• Measured in amperes
– i.e., amps
Fundamentals of Electricity
Resistance (R)
• A material's opposition to the flow of electric
current; measured in ohms.
• Measured in ohms
• All materials, even very good conductors have
some resistance
Fundamentals of Electricity
• Electrons are confined to conductors, i.e., wires
• Electrons flow only through a closed circuit
– Similar to the flow of water in the pipes of a closed hot water
heating system
– Like a pump that provides the force to push water through
the pipe, a battery provides the electrical push, i.e., voltage,
to push electrons through the wire
Fundamentals of Electricity
• Electrons are confined to conductors, i.e., wires
• Electrons flow only through a closed circuit
switch
Closed circuit, current flows
switch
Open circuit, no current flows
Fundamentals of Electricity
• Electrical circuits
switch
Resistance
(resistor)
voltage
battery
current
Fundamentals of Electricity
Relationship between Voltage (E), Current
(I) and Resistance (R)
• It takes a certain force (i.e., voltage) to get a
certain amount of current (amps) to flow
against a specific reststance (ohms)
• A greater resistance requires a greater force
(i.e., higher voltage) to get the same amount of
current to flow
Fundamentals of Electricity
Relationship between Voltage (E), Current (I)
and Resistance (R)
Ohm’s Law
Voltage = Current x Resistance
E=IxR
Volts = amps x ohms
Fundamentals of Electricity
Relationship between Voltage (E), Current (I)
and Resistance (R)
Ohm’s Law
Current = Voltage/Resistance
I=E/R
Resistance = Voltage/Current
R=E/I
Fundamentals of Electricity
Ohm’s Law - Summary
• E is voltage
– Units - volts
• I is current
– Units - amperes
• R is resistance
– Units - ohms
• R = E/I
• I = E/R
• E=IxR
Fundamentals of Electricity
• Electrical circuits – Ohms law
E=IxR
I=E/R
R=E/I
Resistance
voltage
battery
5Ω
10 V
current
2A
If voltage V = 10 volts (10 V) and
resistance R = 5 ohm (1 Ω)
Then current I = E / R = 10 / 5
= 2 amps (2 A)
Fundamentals of Electricity
• Electrical circuits – Ohms law
E=IxR
I=E/R
R=E/I
Resistance
voltage
battery
1/2 Ω
10 V
current
20 A
If voltage V = 10 volts (10 V) and
resistance R = 5 ohm (1 Ω)
Then current I = E / R = 10 / 5
= 2 amps (2 A)
If voltage = 10 V and current = 20 A
Then resistance R = E / I = 10 / 20
=½Ω
Fundamentals of Electricity
• Electrical circuits – Ohms law
E=IxR
I=E/R
R=E/I
Resistance
voltage
battery
100 Ω
300 V
current
3A
If voltage V = 10 volts (10 V) and
resistance R = 5 ohm (1 Ω)
Then current I = E / R = 10 / 5
= 2 amps (2 A)
If voltage = 10 V and current = 20 A
Then resistance R = E / I = 10 / 20
=½Ω
If resistance = 100 Ω and current = 3 A
Then voltage V = I x R = 3 x 100
= 300 V
Fundamentals of Electricity
• Electrical circuits – Ohms law
Resistance
voltage
battery
100 Ω
300 V
current
3A
Fundamentals of Electricity
• Electrical circuits – Ohms law
Resistance
voltage
battery
300 V
100 Ω
300 V
current
3A
300 V
The voltage across the resistor is the same as
the voltage across the battery
Fundamentals of Electricity
• Electrical circuits – Ohms law
Resistance
voltage
battery
100 Ω
300 V
current
3A
Fundamentals of Electricity
• Electrical circuits – Ohms law
3A
Resistance
voltage
battery
100 Ω
300 V
current
3A
3A
The current is the same anywhere in the circuit
Fundamentals of Electricity
Power
•
Moving electrons do work and expend energy:
– generate heat
– generate light
– run motors
– generate and receive radio signals
– compute
•
Power is the rate at which electrical energy is generated or consumer
– measured in the units of Watts
•
Power = voltage x current
P=ExI
Fundamentals of Electricity
•
Power = voltage x current
P=ExI
I = P/E
E = P/I
•
Example 1: 60 watt light bulb
– E = 120v, P = 60w, I = ?, R = ?
Power
60w bulb
120 V
I
Fundamentals of Electricity
•
Power = voltage x current
P=ExI
I = P/E
E = P/I
•
Example 1: 60 watt light bulb
– E = 120v, P = 60w, I = ?, R = ?
I = P/E = 60/120 = ½ A
R = E/I = 120/½ = 240Ω
Power
60w bulb
I
120 V
Resistance
voltage
battery
100 Ω
300 V
current
• Example 2:
– E = 300v, R = 100Ω, I = ?, P = ?
I = E/R = 300/100 = 3A
P = E x I = 300/3 = 300w
Fundamentals of Electricity
Types of Current
• When current flows in only one direction, it is called direct
current (DC).
– batteries are a common source of DC.
– most electronic devices are powered by DC.
• When current flows alternatively in one direction then in the
opposite direction, it is called alternating current (AC).
– your household current is AC.
– radio waves are AC
Fundamentals of Electricity
Electrical Circuits
•
Resistor or
other component
Series circuit
Resistor or
other component
– one and only one path for current flow
battery
current
•
Parallel circuit
– alternative paths for current flow
Resistor or
other component
battery
current
Fundamentals of Electricity
Components: the resistor
• restricts (limits) the flow of
current through it
• unit of resistance: ohm (Ω)
• (also dissipates energy as
heat)
– incadescent lightbulbs
– electric stoves
• Circuit Symbol
Fundamentals of Electricity
Components: the resistor
• Circuit Symbol
• restricts (limits) the flow of
current through it
• unit of resistance: ohm (Ω)
• (also dissipates energy as
heat)
– incadescent lightbulbs
– electric stoves
• A resistor for which the
resistance can be changed is
a variable resistor or
potentiometer
variable
resistor
potentiometer
Fundamentals of Electricity
Components: the resistor
• restricts (limits) the flow of
current through it
• unit of resistance: ohm (Ω)
• (also dissipates energy as
heat)
– incadescent lightbulbs
– electric stoves
• A resistor for which the
resistance can be changed is
a variable resistor or
potentiometer
• Circuit Symbol
Fundamentals of Electricity
Components: the battery
• Circuit Symbol
• source of DC voltage
• stores energy
• provides energy to a circuit
Fundamentals of Electricity
Components: the capacitor
• temporarily stores electrons
and electric current
– stores energy in an
electrostatic field
• Unit of capacitance: farad
• composed of parallel metal
plates with a non-conductive
material (dielectric) in
between
– dielectric can be air, plastic,
glass, etc.
• A capacitor for which the
capacitance can be changed
is a variable capacitor
• Circuit Symbol
Fundamentals of Electricity
Components: the capacitor
• Unit of capacitance: farad
– a coulomb is a unit of electrical charge
– 1 coulomb = 6,250,000,000,000,000,000 electrons
– 1 farad is 1 coulomb/volt
switch
Fundamentals of Electricity
Components: the capacitor
• Unit of capacitance: farad
– a coulomb is a unit of electrical charge
– 1 coulomb = 6,250,000,000,000,000,000 electrons
– 1 farad is 1 coulomb/volt
switch
Fundamentals of Electricity
Components: the capacitor
• Unit of capacitance: farad
– a coulomb is a unit of electrical charge
– 1 coulomb = 6,250,000,000,000,000,000 electrons
– 1 farad is 1 coulomb/volt
switch
Fundamentals of Electricity
Components: the capacitor
• Unit of capacitance: farad
– a coulomb is a unit of electrical charge
– 1 coulomb = 6,250,000,000,000,000,000 electrons
– 1 farad is 1 coulomb/volt
switch
Fundamentals of Electricity
Components: the capacitor
• Unit of capacitance: farad
– a coulomb is a unit of electrical charge
– 1 coulomb = 6,250,000,000,000,000,000 electrons
– 1 farad is 1 coulomb/volt
switch
Note: once the capacitor is charged, no more current flows, and the
capacitor acts like an open circuit (an open switch)
Fundamentals of Electricity
Components: the capacitor
• Unit of capacitance: farad
– a coulomb is a unit of electrical charge
– 1 coulomb = 6,250,000,000,000,000,000 electrons
– 1 farad is 1 coulomb/volt
switch
Fundamentals of Electricity
Components: the capacitor
• Unit of capacitance: farad
– a coulomb is a unit of electrical charge
– 1 coulomb = 6,250,000,000,000,000,000 electrons
– 1 farad is 1 coulomb/volt
switch
Fundamentals of Electricity
Components: the capacitor
• Unit of capacitance: farad
– a coulomb is a unit of electrical charge
– 1 coulomb = 6,250,000,000,000,000,000 electrons
– 1 farad is 1 coulomb/volt
switch
Fundamentals of Electricity
Components: the capacitor
• Unit of capacitance: farad
– a coulomb is a unit of electrical charge
– 1 coulomb = 6,250,000,000,000,000,000 electrons
– 1 farad is 1 coulomb/volt
switch
Fundamentals of Electricity
Components: the capacitor
• Unit of capacitance: farad
– a coulomb is a unit of electrical charge
– 1 coulomb = 6,250,000,000,000,000,000 electrons
– 1 farad is 1 coulomb/volt
switch
~
AC voltage
Fundamentals of Electricity
Components: the capacitor
• Unit of capacitance: farad
– a coulomb is a unit of electrical charge
– 1 coulomb = 6,250,000,000,000,000,000 electrons
– 1 farad is 1 coulomb/volt
switch
~
AC voltage
Note: a capacitor allows AC current to flow
Fundamentals of Electricity
Components: the capacitor
• Capacitive reactance (XC)
– the opposition to alternating current due to capacitance
– unit of capacitive reactance: ohms
– is inversely proportional to the signal frequency and the
capacitance
– XC = - 1 / (2fC)
• Note: if f = 0, i.e. DC current, XC = ∞, i.e., an open circuit
Fundamentals of Electricity
Components: the inductor
• stores electric current
– stores energy in a magnetic
field
– any wire with a current
flowing through it creates a
magnetic field
• unit of inductance: henry
• magnetic field is
strengthened by coiling wire,
i.e., inductance is increases
• an inductor for which the
inductance can be changed
is a variable inductance
• An inductor may have an
iron core to increase the
inductance
• Circuit Symbol
Fundamentals of Electricity
Components: the inductor
• Inductive reactance (XL)
– the opposition to alternating current due to inductance
– unit of inductance reactance: ohms
– is proportional to the signal frequency and the inductance
– XL = + 2fL
• Note: if f = 0, i.e. DC current, XL = 0, i.e., an short circuit
Fundamentals of Electricity
Impedance (Z):
• Impedance is the total opposition to alternating current due to
reistance, capacitance and inductance
– unit of impedance: ohms
– Z = √ R2 + (XC + XL)2
• Resonance:
~
When XC = XL,
Then Z = R
AC voltage
Fundamentals of Electricity
Components: the transistor
•
•
controls the flow of current
Circuit Symbol
– like an electronically controlled
valve.
– like the faucet in your sink
•
used to amplify a signal or as an
on-off switch
– A small current or voltage on
the “base (B)” lead causes a
large change in the current
flowing between the “emitter
(E)” and “collector (C)” leads
C
B
E
Fundamentals of Electricity
Components: the transistor
•
•
controls the flow of current
Circuit Symbol
– like an electronically controlled
valve.
– like the faucet in your sink
•
used to amplify a signal or as an
on-off switch
– A small current or voltage on
the “base (B)” lead causes a
large change in the current
flowing between the “emitter
(E)” and “collector (C)” leads
C
B
E
Fundamentals of Electricity
Components: the transistor
•
•
controls the flow of current
Circuit Symbol
– like an electronically controlled
valve.
– like the faucet in your sink
•
used to amplify a signal or as an
on-off switch
– A small current or voltage on
the “base (B)” lead causes a
large change in the current
flowing between the “emitter
(E)” and “collector (C)” leads
C
B
E
Fundamentals of Electricity
Components: the transistor
•
controls the flow of current
– like an electronically controlled
valve.
– like the faucet in your sink
•
used to amplify a signal or as an
on-off switch
– A small current or voltage on
the “base (B)” lead causes a
large change in the current
flowing between the “emitter
(E)” and “collector (C)” leads
•
Circuit Symbol
Fundamentals of Electricity
Components: the integrated circuit
• a collection of components
contained in one device
– replaces many individual
components
– a “black-box” for a specific
function
– examples:
•
•
•
•
•
amplifier
switch
voltage regulator
mixer
display controller
•
Circuit Symbol
Fundamentals of Electricity
Components: diode
•
•
Circuit Symbol
Allows current to flow in only
one direction
Components: light emiting diode (LED)
•
Special type of diode that emits
light when current passes
through it
Components: fuses and circuit breakers
•
interrupts the flow of current if the
current exceeds some value
– Fuses blow – one time protection.
– Circuit breakers trip – can be reset
and reused.
•
Circuit Symbol
Fundamentals of Electricity
Other Circuit Symbols:
Fundamentals of Electricity
Circuit Diagrams: examples
Amplifier
Fundamentals of Electricity
Light control
Antenna tuner
Power supply – converts 120VAC to DC
Fundamentals of Electricity
Very Large and Very Small Numeric Values: Units
• resistor values may be ohms
(Ω), kilo ohms (kΩ) or mega ohms
(MΩ)
• capacitor values typically are
microfarads (μf) or pico farads (pf)
• inductance values are typically
milli henrys (mh) or micro henrys
(μh)
• frequencies are typically kilo
hertz (kHz) or mega Hertz (MHz)
• voltage is often volts (V) milli
volts (mV) or micro volts (μV)
• current is often amps (A), milli
amps (mA) or micro amps (μA)
Fundamentals of Electricity
Very Large and Very Small Numeric Values: decibels (dB)
•
decibels are used to compare values that vary over a very large range
–
signal levels, amplifier gain, sound levels
•
decibles compare values on a logrithmic scale
•
3 dB is a factor of 2
– a 3 dB gain in an amplifier means that the output level is twice the input level
•
10 dB is a factor of 10
– a 10 dB gain in an amplifier means that the output level is 10 times the input level
•
decibels add:
– 3 dB = 2 times
– 6 dB = 2 x 2 = 4 times
– 9 dB = 2 x 2 x 2 = 8 times
– 12 dB = 2 x 2 x 2 x 2 = 16 times
– 10 dB = 10 times
– 20 dB = 10 x 10 = 100 times
– 30 dB = 10 x 10 x 10 = 1000 times