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Chapter#16
Introductory Electronics
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• SLO#16.1.1
• Explain the process of thermionic
emission emitted from a filament
Thermionic emission is
the phenomenon of emission of
electrons from the surface of a
metal, when it is heated to a high
temperature.
OR
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When a metal is heated some
of the electrons may gain enough
energy to escape from the surface
of metal. This effect is called
thermionic emission.
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Thermionic emission can
also be produced by electrically
heating metals like tungsten,
tantalum, throated tungsten and
metals coated with oxides of
barium, strontium etc. are
commonly used.
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• SLO#16.2.1
• Describe the simple construction and use of an
electron gun as a source of electron beam
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• Electron gun consists of a glass tube at
very low pressure.
Tungsten filament heated by 6 V.
• A beam of electron produces a supply.
A high +ve potential is applied to
cylindrical anode to accelerate the
electron to a high speed and they shoot
straight through the hole of the anode as
a fine beam of electrons. This beam of
electron is cathode ray because they are
emitted from cathode.
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• SLO#16.3.1
• Describe the effect of electric field on an electron beam
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An electric field can be produced
between two parallel plates placed
horizontally some distance apart
by applying potential difference
across them. When electron beam
passes between two plates, the
electrons are deflected toward the
positive plate.
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• It is found greater the electric field
strength, greater would be degree
of deflection of the electron beam.
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• SLO#16.4.1
• Describe the effect of magnetic field on an electron beam
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• The electron beam passes through
the magnetic field between poles of
a magnet at right angle.
The electron beam is deflected by
the magnetic field.
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• The Fleming's left hand rule is
applied to determine the direction
of deflection by considering that
electron beam is equivalent to
positive are conventional current in
opposite direction. We find that
deflection in downward
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• SLO#16.5.1
• Describe the basic principle of
CRO and make a list of uses
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• Cathode ray oscilloscope is a
versatile
and
exciting
application of the effect of
electric
field
on
charged
particles. The cathode rays as
the name suggests are rays
coming from the negative
electrode (cathode).
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•
Cathode ray oscilloscope is
used to measure the voltage
and time and show how voltage
varies with time. It do this by
drying graph on screen.
• The vertical scale represent
voltage and horizontal scale
time.
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• The cathode ray oscilloscope
uses narrow beam of electrons
to trace out wave form and
other signals on fluorescent
screen. The beam of electrons
produces
bright
spot
on
fluorescent
screen.
By
deflecting the beam of electrons
the spot can be moved.
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• There are two sets of deflecting
plates. The y-plates move the
beam vertically by connecting
A.C supply across the y-input
terminals. The X-plates move
the
beam
horizontally.
Normally the movement is
produced by a circuit called time
base inside the oscilloscope.
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• USES OF CATHODE RAY OSCILLOCOPE
• Measuring peak voltage:
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• To measure voltage gain control is
set at 5 v/cm. this means that spot
moves 1cm vertically for every 5
volts across the Y-input terminal.
The amplitude represent the peak
voltage on wave form. As the
amplitude is 2cm.
• Peak voltage = 2cm x 5v/cm = 10v.
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• Measuring time and frequency:
To measure the time,
the time base control is set at 10ms/cm.
This means that spot take 10ms
(millisecond) to move one 1cm
horizontally. As the horizontal peak to
distance is 4.0cm.
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• Peak to peak time = 4cm x 10ms/cm =
40ms.
= 0.04 sec.
• This means spot take 0.04sec to trace
one complete cycle this time is called
period.
F = 1/T = 1/0.04 = 25Hz.
Frequency is 25 Hz.
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• SLO#16.6.1
• Differentiate between analogue and digital
electronics
• All of electronics can be divided into
two broad categories analog and
digital.
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a. Analogue electronics:
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• In analogue method the
information is converted into
electrical voltage or currents that
vary continuously. For example
microphone converts sound waves
into continuous electrical signals
which are then amplified and then
fed into sound-speaker.
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• Examples of analogue system: T.V
and radio volume, conventional
watches with needles are the
examples of analogue system:
• Analogue meters display their
reading by the deflection of pointer
over continuous scale. They gives
the value of current, voltage and
resistance by the deflection of
needles.
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• Digital electronics:
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• In digital electronics the
information is converted into
electrical voltage that have only one
of two values either high (5V) or
low (0V).
• They include switching type circuits.
A switch is a digital device which
allow a lamp to be either on or off.
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• Example of digital system:
• Digital multimeters , digital
watches, digital computers are
popular examples of digital system
because they display their readings
as digits.
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• SLO#16.6.2
• Describe that digital signals can carry more information
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• In digital system information can be
stored easily and also can be
processed easily.
• Digital system can be designed
easily with the help of integrated
circuits (IC’s) and hundreds of IC’s
are available. Maintenance of digital
system is easy and they are
cheaper, Digital system require less
power and it s results are accurate.
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• SLO#16.17.1
• State the basic operations of digital electronics
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• There are three basic operations of
digital electronics which are AND
operation, OR operation and NOT
operation are required to determine
the value of output if the values of
input variables of a circuit are
known are called basic operations of
digital electronics.
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• SLO#16.18.1
• Identify and draw the symbols for the logic gates
• (NOT,OR ,AND,NOR and NAND)
1.NOT GATE:
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2.OR GATE:
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3. AND GATE:
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4. NOR GATE:
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5.NAND GATE:
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• SLO#16.8.2
• State the action of the logic gates in truth
table from with two inputs
• Logic gates:-
Electronic switches which
controls video recorders, security
lamps, alarm system are called
logic gates.
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• In practical logic gates works
electronically using tiny
transmitters as switches. They are
manufactured as integrated circuits
(IC’s) with each chip holding
several gates. The chip also needs
D.C power supply. Typically this is
a 5 V supply, with one terminal
marked 5V and 0Volts.
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•
Logic gates are the combinations
of electronic switches. These
switches are operated by applying
voltages to the input of the logic
gates. The input can be high (5V)
or low (0V). The output of a logic
gate is also a voltage that can be
high or low.
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• Logic gates are usually made in the
form of integrated circuits (IC’s)
each IC has many logic gates made
on tiny piece of silicon packed in
plastic.
• Logic gates are used in switching
circuits, computers and other
electronic systems.
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• They open and give a high out put
voltages i.e (5V) depending on
combination of voltages at their
inputs. Which is usually more than
one?
• There are three logic gates AND
Gate, OR Gate and NOT Gate.
Their symbols and truth tables are
shown in figure.
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• AND Gate:Its output is high, if inputs A and B are high
X = A.B
It read as X equal A AND B.
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• OR Gate:-
Its output is high if its at least one
of its input is high.
X = A+B
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• NOT Gate:Its output is high, if input is low and vice versa.
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• NAND Gate:
•
It is equivalent to AND Gate with its output is
inverted by NOT Gate.
• Its output is high if input A and B are not both high.
X = A.B
It is read as X equals A AND B NOT.
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• NOR Gate:
•
It is equivalent to OR Gate
but output is inverted by NOT Gate.
• It’s output is high if neither input A
NOR input B is high.
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• SLO#16.8.3
• Describe the simple uses of logic gates
• A gate can add, subtract, count, make
simple decisions and even store
information’s.
• Gate is the basic building block of digital
system. A gate is like a switch. It is
either ON or OFF.
• ON represents logic 1 and OFF logic 0.
• Gates are also called digital circuits, logic
circuits and switching circuits.
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