Download Chapter 3 Electricity

Chapter 3
Electricity, Components and Circuits
Chapter 3
Electricity, Components & Circuits
Today’s agenda
• Fundamental concepts of electricity & circuits
• Voltage & current
• Resistance, capacitance & inductance
• Reactance, impedance & resonance
• Common types of electronic components
• How basic types of radios are made
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Chapter 3
Electricity
Electric current (represented by the letter “I”) is the flow
of electrons. Current is measured in amperes (A) with
an ammeter. Amperes are abbreviated as “amps”.
Current is always measures as the flow through
something (e.g., wire, electronic component, etc).
Voltage (represented by the letter “E”) is the
electromotive force that makes electrons move and
voltage is measured in “volts” (“V” or “v”) with a
voltmeter.
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Chapter 3
Electricity
The polarity of voltage is either positive or negative.
• Negative voltage repels electrons
• Positive voltage attracts electrons
The Earth’s surface acts as the universal reference for
voltage measurements and is called “earth ground”,
“ground potential” or simply “ground”.
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Chapter 3
Electricity
A circuit is any path through which current can flow.
If two or more devices are connected in a circuit so that
the same current must flow through all of them in
sequence, that is called a “series” circuit.
#1
Series
Circuit
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Chapter 3
Electricity
If two or more devices are connected in a circuit so that
the same voltage is present across all of them at the same
time, that is called a “parallel” circuit.
Parallel
Circuit
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Chapter 3
Electricity
Voltmeters are connected in parallel with a component or
circuit to measure voltage. Whereas, ammeters are
connected in series with a component or circuit to measure
current.
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Chapter 3
Electricity
A “closed circuit” provides an uninterrupted, endless path
for the flow of current. This is normally done intentionally
by design.
An “open circuit” is made by breaking the path of current in
a circuit.
A “short circuit” is a direct connection between two points
in a circuit. Although similar to a “closed circuit”, “short
circuits” are usually unintentional.
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Chapter 3
Electricity
The basic electrical test
instruments are simple meters:
• Voltmeters
• Ammeters
• Ohmmeters
All of these meters are found in the
common and relatively inexpensive
“multimeter”. They come in analog
and digital to measure voltage,
current and resistance.
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Chapter 3
Electricity
Multimeters can tell you a lot:
If you are measuring the resistance of a
circuit and the reading starts out low but
gradually increases, that indicates the
presence of a large value capacitor.
The flexibility of the multimeter means
that it’s important to use it properly.
Measuring voltage or connecting the
probes to a “live” circuit when the meter
is set to measure resistance is a common
way to damage a multimeter.
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Chapter 3
Electricity
All materials impede the flow of electrons to some degree.
This property is called “resistance”. Resistance is the
opposition of a material to current flow.
Resistance (represented by the letter “R”) is measured in
ohms (represented by the Greek letter Omega (Ω)) with an
ohmmeter.
If you know any two of current (I), voltage (E) and resistance
(R), you can calculate the missing value
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Chapter 3
Electricity
Materials in which electrons flow easily in response to an
applied voltage are “conductors”.
Materials such as copper and gold are good conductors as
is salt water. So is the human body!
Materials that resist or prevent the flow of electrons are
“insulators”. Glass, ceramic, plastic, dry wood and paper
and other non-metals are examples of “insulators”.
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Chapter 3
Electricity
Georg Ohm discovered the proportional
relationship between voltage, current and
resistance in 1827.
Ohm’s Law states that current is directly
proportional to voltage and inversely
proportional to resistance.
Georg Ohm
The more a material resists the flow of electrons, the lower
the current will be in response to voltage across the
material.
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Chapter 3
Electricity
If you know any two of I, E
or R, you can determine
the missing value.
As an equation, we can
state that I = E / R, E = I x R
and R = E / I.
E=IxR
I=E/R
R=E/I
Current (I) equals voltage (E) divided by resistance (R).
Voltage (E) equals current (I) multiplied by resistance (R).
Resistance (R) equals voltage (E) divided by current (I).
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Chapter 3
Electricity
What is the resistance of a
circuit in which a current of 3
amperes flows through a
resistor connected to 90 volts?
E=IxR
I=E/R
R=E/I
Resistance (R) equals voltage (E) divided by current (I).
R=E÷I
R = 90V ÷ 3A
R = 30 ohms or 30Ω
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Chapter 3
Electricity
What is the resistance of a
circuit in which the applied
voltage is 12 volts and the
current flow is 1.5 amperes?
E=IxR
I=E/R
R=E/I
Resistance (R) equals voltage (E) divided by current (I).
R=E÷I
R = 12V ÷ 1.5A
R = 8 ohms or 8Ω
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Chapter 3
Electricity
E=IxR
What is the resistance of a
circuit that draws 4 amperes
from a 12-volt source?
I=E/R
R=E/I
Resistance (R) equals voltage (E) divided by current (I).
R=E÷I
R = 12V ÷ 4A
R = 3 ohms or 3Ω
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Chapter 3
Electricity
What is the current of a circuit
with an applied voltage of 120
volts and a resistance of 80
ohms?
E=IxR
I=E/R
R=E/I
Current (I) equals voltage (E) divided by resistance (R).
I=E÷R
I (current) = 120V ÷ 80Ω
I = 1.5 amperes or 1.5A
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Chapter 3
Electricity
What is the current flowing
through a 100-ohm resistor
connected across 200 volts?
E=IxR
I=E/R
R=E/I
Current (I) equals voltage (E) divided by resistance (R).
I=E÷R
I (current) = 200V ÷ 100Ω
I = 2 amperes or 2A
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Chapter 3
Electricity
What is the current flowing
through a 24-ohm resistor
connected across 240 volts?
E=IxR
I=E/R
R=E/I
Current (I) equals voltage (E) divided by resistance (R).
I=E÷R
I (current) = 240V ÷ 24Ω
I = 10 amperes or 10A
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Chapter 3
Electricity
What is the voltage across a
2-ohm resistor if a current of 0.5
amperes flows through it?
E=IxR
I=E/R
R=E/I
Voltage (E) equals current (I) multiplied by resistance (R).
E=IxR
E = 0.5A x 2Ω
E = 1 volt or 1V
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Chapter 3
Electricity
What is the voltage across a
10-ohm resistor if a current of
1 ampere flows through it?
E=IxR
I=E/R
R=E/I
Voltage (E) equals current (I) multiplied by resistance (R).
E=IxR
E = 1A x 10Ω
E = 10 volt or 10V
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Chapter 3
Electricity
What is the voltage across a
10-ohm resistor if a current of
2 amperes flow through it?
E=IxR
I=E/R
R=E/I
Voltage (E) equals current (I) multiplied by resistance (R).
E=IxR
E = 21A x 10Ω
E = 20 volt or 20V
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Chapter 3
Electricity
P=ExI
Power (represented by the
letter “P”) is measured in watts
which are abbreviated as “W”.
P = E2 / R
Power is the rate at which
electrical energy is used.
I=P/E
P = I2 x R
E=P/I
Power is measured with a wattmeter.
Power (P) equals voltage (E) multiplied by current (I).
As with Ohm’s Law, if you know any two of P. E or I you
can determine the missing quantity.
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Chapter 3
Electricity
P=ExI
How much power is being used
in a circuit when the applied
voltage is 13.8 volts and the
current is 10 amperes?
P = E2 / R
P = I2 x R
X
I=P/E
E=P/I
Power (P) equals voltage (E) multiplied by current (I).
P=ExI
E = 13.8V x 10A
E = 138 watts or 138W1 July 2010-30 June 2014 Technician
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Chapter 3
Electricity
P=ExI
How much power is being used
in a circuit when the applied
voltage is 12 volts and the
current is 2.5 amperes?
P = E2 / R
P = I2 x R
X
I=P/E
E=P/I
Power (P) equals voltage (E) multiplied by current (I).
P=ExI
E = 12V x 2.5A
E = 30 watts or 30W
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Chapter 3
Electricity
P=ExI
How many amperes are flowing
in a circuit when the applied
voltage is 12 volts and the load
is 120 watts?
P = E2 / R
P = I2 x R
?
I=P/E
E=P/I
Current (I) equals power (P) divided by voltage (E).
I=P÷E
I = 120W ÷ 12V
I = 10 amperes or 10A1 July 2010-30 June 2014 Technician
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Chapter 3
Electricity
AC and DC
It’s electricity – not a rock
band.
Current that flows in one
direction all the time is
“direct current” or “dc”.
Direct Current
Alternating Current
Current that regularly
reverses direction is
“alternating current” or
“ac”
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Chapter 3
Electricity
Like current, a voltage that has the same polarity (the same
direction from positive to negative) is “direct current” or
“dc”.
A voltage that regularly reverses polarity is an ac voltage.
Batteries and solar cells are a source of dc voltage and
current.
Household power is suppled by an electrical utility in the
form of ac voltage and current.
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Chapter 3
Electricity
Just like radio waves, a complete sequence of ac current
flowing, stopping, reversing and stopping again is a
“cycle”.
The number of cycles per second is the ac current’s
frequency. The same is true for voltage.
The frequency of household ac voltage is 50 or 60 Hz while
radio signals used by radio amateurs have frequencies in
the MHz and GHz range.
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Chapter 3
Components & Units
Electronic circuits are made from components, each of
which performs a discrete function: storing or dissipating
energy, routing current or amplifying a signal.
The three most basic types of electronic components are
“resistors”, “capacitors” and “inductors” (aka “coils”).
The amount of resistance in a resistor is measured in
“ohms”(Ω), “kilo-ohms” (kΩ) and “mega-ohms” (MΩ).
Just like a valve in a water pipe restricts the flow of water, a
resistor opposes or restricts the flow of electrical current.
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Chapter 3
Components & Units
The value of a resistor is
determined by a color code
system.
Resistors come in fixed and
variable values.
A variable resistor is called a
“potentiometer” or “pot” and is
used to adjust voltage as in
volume control.
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Chapter 3
Components & Units
The schematic symbol for a fixed resistor:
Fixed
The schematic symbol for a variable resistor:
Variable
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Chapter 3
Components & Units
5%
4
7
100
47 x 100 = 4700 W ± 5%
or
47 x 100 = 4.7k W ± 5%
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Chapter 3
Components & Units
Capacitors store electrical energy in the electric field
created by a voltage between two conducting surfaces (e.g.,
metal foil) called “electrodes” and separated by an
insulating material called a “dialectric”.
Storing energy in this manner is called “capacitance” and is
measured in farads (F). Remember: frequency is
symbolized by the lower case “f”
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Chapter 3
Components & Units
Capacitors used in radio circuits have
values measured in “picofarads” (pF),
“nanofarads” (nF) and “microfarads” (μF).
Capacitors are used to smooth out ac
voltage changes.
A capacitor cannot pass dc current.
Michael Faraday
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Chapter 3
Components & Units
Like all components, capacitors come
in many shapes, sizes and values.
Fixed
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Chapter 3
Components & Units
Electrolytic capacitors
(polarized) are used as
rectifier and power supply
filters
+
Electrolytic
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Chapter 3
Components & Units
“Variable” or “Tuning”
capacitors vary the
frequency of resonant
circuits/filters and adjust
impedance matching circuits
Variable
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Chapter 3
Components & Units
Inductors store magnetic energy in the
magnetic field created by current flowing
through a wire. Inductors smooth out
current changes.
This is called inductance and it is measured
in nano-henrys (nH), micro-henrys (μH),
milli-henrys (mH) and henrys (H).
Joseph Henry
Inductors are made of wire wound in a coil, sometimes
around a core of magnetic material that concentrates the
magnetic energy.
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Chapter 3
Components & Units
Inductors
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Chapter 3
Components & Units
Schematic symbols for inductors
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Chapter 3
Components & Units
Transformers are made from two or more inductors that
share their stored energy. This allows energy to be
transferred from one inductor to another while changing
the combination of voltage and current.
A transformer is used to transfer energy from a home’s
120 V ac outlet to a lower voltage for use in electronic
equipment.
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Chapter 3
Components & Units
Transformer schematic
symbols
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Chapter 3
Components & Units
All three types of basic components are available as “adjustable” or
“variable” models.
A variable resistor is also called a “potentiometer” or “pot”.
Variable resistors are used to adjust voltage or potential, such as for volume
control.
Variable capacitors and inductors are used to tune radio circuits for a variety
of purposes.
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Chapter 3
Components & Units
Variable inductor
Variable
Resistors
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Variable capacitor 46
Chapter 3
Components & Units
Reactance and Impedance
In a resistor, ac voltages and currents are exactly in step
(“in phase”): When voltage increases so does current and
vice-versa.
In capacitors and inductors, the relationship between ac
voltage and current is changed so that there is an “offset”
in time between changes as energy is stored and released.
This means that voltage and current have a phase
difference.
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Chapter 3
Components & Units
Reactance and Impedance
In a capacitor, the change in current occurs ahead of
voltage changes because of the smoothing action of the
capacitor.
In an inductor, changes in the ac current lag behind
changes in voltage because the inductor resists changes in
current.
Opposition to ac current flow is called “reactance” and is
represented by “X” and is measured in ohms – just like a
resistance.
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Chapter 3
Components & Units
Reactance and Impedance
Reactance from a capacitor is called “capacitive reactance”.
Reactance from an inductor is called “inductive reactance”.
The combination of resistance and reactance is called
“impedance” and is represented by the letter “Z” and is also
measured in ohms.
Radio circuits almost always have both resistance and
reactance.
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Chapter 3
Types of Radios & Radio Circuits
Resonance
In a circuit with both capacitive and inductive reactance, at
some frequency the two types of reactance will be equal
and cancel each other out. As a result, the ac current and
voltage are back in step with each other. This condition is
called “resonance”.
The frequency at which resonance occurs is call the
“resonant frequency”.
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Chapter 3
Types of Radios & Radio Circuits
Resonance
Circuits that contain both capacitors and inductors will
have at least one resonant frequency and are called
“resonant circuits” or “tuned circuits”.
Tuned circuits act as “filters” either passing or rejecting
signals at the resonant frequency.
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