Transcript Electrical Principles Wk 2B

Electrical Principals
Chapter 4
Conductors, Conductance, Insulators,
Resistivity, Temperature on Conductors,
Resistors, Resistor Types, Resistor Values,
Variable Resistors, Capacitors, Diodes,
Transistors, Digital Logic Gates,
Conductors, Temperature
Effects on Conductors, and
Insulators
Conductors
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A Conductor is a material that has
very little resistance and permits
electrons to move through it easily.
Conductors include wire, cable, and
cord.
Electrical circuits and components are
connected using Conductors.
Conductors
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Conductor material include copper,
aluminum, copper-clad aluminum, steel, and
bronze.
Copper and Aluminum are the most
commonly used materials.
Copper is most common.
Copper is preferred because it has a lower
resistance than aluminum for any given wire
size.
Conductors
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Conductance is the measure of how
good a conductor is at carrying
current.
Conductance is inversely proportional
to resistance.
A good Conductor has a high
Conductance value and a very small
resistance to current flow.
Conductors
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Conductors are not meant to offer
any resistance or opposition to current
flow.
Conductance is the measure of how
good a Conductor is, and even the
best Conductors have some value of
resistance.
We can calculate a Conductor’s
resistance with the formula R=V/I
Temperature Effects on
Conductors
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When heat is applied to a Conductor,
the atoms within the Conductor
convert this thermal energy into
mechanical energy or movement.
These random moving atoms cause
collisions between the directed
electrons (current flow) and the
adjacent atoms, resulting in an
opposition to current flow (resistance).
Temperature Effects on
Conductors
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This means the greater the heat
applied to the conductor (more current
flowing), the greater the atom
movement, causing more collisions of
atoms to occur and consequently,
greater conductor resistance.
More current more heat. More heat
more resistance.
Insulators
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Insulators is any material that offers
high resistance or opposition to current
flow.
Remember Conductors permit the
easy flow of current.
Insulators can, with sufficient
pressure or voltage applied across
them, “break down” and conduct
current.
Resistors, Resistance,
and
Resistivity
Resistivity
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Resistivity is the resistance (in Ohms)
that a certain length of conductive
material (in feet) will offer to the flow of
current.
Resistors, Resistance, and
Resistivity
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Electrical Resistance is opposition to
the flow of electrons through any
material.
A Resistor is a device that limits the
current flowing in an electronic circuit.
Resistors are classified by their
resistance value (in Ώ) and their power
dissipation (in Watts).
Resistors, Resistance, and
Resistivity
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Resistors are used for dividing
voltage, reducing voltage, developing
heat, and limiting current.
Resistors may be fixed, variable or
tapped.
A Fixed Resistor is a Resistor with a
set value, such as 100Ώ.
Resistors, Resistance, and
Resistivity
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A Variable (adjustable) Resistor is a
resistor with a set range of values,
such as 0Ώ to 1000Ώ.
A Tapped Resistor is a resistor that
contains fixed tap points of different
resistances.
A Thermistor is a device that changes
resistance with a change in
temperature. Thermistors are
semiconductor devices.
Resistors, Resistance, and
Resistivity
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There are two types of Thermistors –
positive temperature coefficient (PTC) and
the negative temperature coefficient (NTC).
A PTC Thermistor has an increasing
resistance value with an increase in
temperature.
A NTC Thermistor has a decreasing
resistance value with an increasing in
temperature. The NTC Thermistor is the
most common type.
Resistors, Resistance, and
Resistivity
Capacitance, Capacitors,
Diodes and Transistors
Capacitance, Capacitors,
and Diodes
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Capacitance is the ability to store
energy in the form of an electrical
charge.
Capacitance is the property of an
electric device that permits the storage
of electrically separated charges when
potential differences exist between the
conductors.
Capacitance, Capacitors,
and Diodes
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A Capacitor is an electric device
designed to store electrical energy by
means of an electrostatic field.
Capacitors are used as filters in AC
circuits to block DC voltages in
electronic circuits, and to improve
torque in motors.
Capacitance, Capacitors,
and Diodes
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Capacitors include fixed, variable, and
electrolytic polarized.
Once Capacitors are discharged, the
must be recharged.
Tolerance of some Capacitors is
indicated by a letter code following the
number.
Capacitance, Capacitors,
and Diodes
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A Diode is a semiconductor device
that offers very high opposition to
current flow in one direction and very
low opposition to current flow in in the
opposite direction.
Diodes are also know as Rectifiers
because they change AC into pulsating
DC.
Capacitance, Capacitors,
and Diodes
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Diodes are rated according to their
type, voltage, and current capacity.
The most common types of diodes
include zener, tunnel, photoconductive,
and light-emitting diodes (LED).
Diodes are a available in current
ranges of a few milliamps to over
1000A.
Capacitance, Capacitors,
and Diodes
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A Zener Diode is a silicon PN junction that
differs from a standard diode in that it
operates in the reverse breakdown region.
A Zener Diode operates as a voltage
regulator in an electronic circuit.
Zener Diodes allow varying amounts of
reverse current flow through them and
continue to maintain a relatively constant
voltage drop when reverse biased.
Capacitance, Capacitors,
and Diodes
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A Tunnel Diode is a diode designed so that
the current flowing through the diode
decreases with an increase in applied
voltage for a specific range of forward
voltage.
Tunnel Diodes operate as an amplifier or
oscillator in an electronic circuit.
Tunnel Diodes exhibit negative resistance
when operated within a specific range of
forward voltage.
Tunnel Diodes are used in logic circuits
and for level sensing.
Capacitance, Capacitors,
and Diodes
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A Photoconductive Diode is a diode
that conducts current when energized
by light.
Photoconductive Diodes decrease
resistance as light increases.
The Diode is made of photosensitive
material that decreases in resistance
with an increase in light.
Capacitance, Capacitors,
and Diodes
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A Light Emitting Diode (LED) is a
Diode that emits light when forward
current is applied.
In an LED is produced when current is
passed through the diode.
LEDs are commonly used as visual
indicators because they have a very
long life.
Capacitance, Capacitors,
and Diodes
Transistors
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A Transistor is a three-terminal device that
controls current through the device
depending on the amount of voltage applied
to the base.
Transistors are made of semiconductor
material.
Transistors are used to start and stop
(switch) current flow or to increase (amplify)
current flow in DC circuits.
Transistors
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Transistors can be NPN or PNP,
Unijunction, and Junction FieldEffect Transistors (JFET), and
Phototransistors.
An NPN Transistor is a transistor that
is formed by sandwiching a thin layer
of P-type material between two layers
of N-type material.
Transistors
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An PNP Transistor is a transistor that is
formed by sandwiching a thin layer of Ntype material between two layers of P-type
material.
NPN and PNP transistors function as a
switch. They start, stop, or increase the flow
of current in a DC circuit.
Transistors also function as amplifiers in
allowing a very small current to control a
much larger current.
Transistors
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A Unijunction Transistor (UJT) is a
transistor consisting of N-type material with
a region of P-type material doped within the
N-type material.
A UJT is used in timer circuits.
A Junction Field-Effect Transistor (JFET)
is a device in which output current is
controlled by the voltage on the input.
Transistors
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A Phototransistor is a transistor that
controls the amount of current flowing
through the emitter/base junction based on
the amount of light.
Phototransistors include NPN and PNP
transistors.
There is an increase of current flow with an
increase in light. A Phototransistor is a
combination of a Photodiode and a
Transistor.
Transistors
Digital Logic Gates
Digital Logic Gates
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A Digital Logic Gate is a circuit that
performs a special logic operation such as
AND, OR, NOT, NOR, NAND, and
exclusive OR.
Digital Logic Gates are used in most
electronic devices.
Digital circuits operation on binary signals.
Binary signals have two states – the signal
is high (1) or low (0) … on (1) or off (0).
Digital Logic Gates
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