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CHAPTER 1: BASIC PHYSICAL CONCEPTS
ATOMS
All matter is made up of countless tiny particles whizzingaround.
Each element has its own unique type of particle,known as its atom .
Atoms of different elements are always different. The slightest change in an atom can make a
tremendous difference in its behavior.
NUCLEUS
The part of an atom that gives an element its identity Made up of two kinds of particles, the proton and the
neutron.
PROTONS AND NEUTRONS
About the same mass , but the proton has an electriccharge while the neutron does not.
The negative charges therefore exactly cancel out thepositive ones, and the atom is electrically neutral .
ATOMIC NUMBER
Gives the element its identity. As the number of protons increases , the number ofneutrons also increases .
Elements with high atomic numbers are much denserthan elements with low atomic numbers.
ISOTOPES
The number of neutrons can vary but the elementkeeps its identity, based on the atomic number.
Differing numbers of neutrons result in various isotopesfor a given element.
ATOMIC WEIGHT
Approximately equal to the sum of the number ofprotons and the number of neutrons in the nucleus.
ELECTRONS
An electron has exactly the same charge quantity as aproton, but with opposite polarity .
One of the earliest ideas about the atom is like raisins in a cake .Later, the electrons were seen as orbiting the nucleus, makingthe atom like a miniature solar system with the electrons as theplanets.
SHELLS
Spheres where the electron are orbiting.
The farther away from the nucleus the shell, the moreenergy the electron has.
In any case, it is far easier to move electrons than it is to moveprotons. Electrons are much lighter than protons or neutrons.
IONS
If an atom has more or less electrons than neutrons,that atom acquires an electrical charge.
A shortage of electrons results in positive charge An excess of electrons gives a negative charge. The elements identity remains the same, no matter
how great the excess or shortage of electrons.
COMPOUNDS
Different elements join together to share electrons Compounds often, but not always, appear greatly
different from any of the elements that make them up.
MOLECULES
The resulting particles when atoms of elements join
together to form a compound. The natural form of an element is also known as itsmolecule.
CONDUCTORS
A substance in which the electrons are mobile.
Pure Elemental Silver is the best conductor at room temperature
Copper and aluminum are also excellent electrical conductors.
Iron, steel, and various other metals are fair to good conductorsof electricity.
In most electrical circuits and systems, copper or aluminum wire
is used. Silver is impractical because of its high cost.
Liquid:Mercury is a good electrical conductor.Salt water is a fair conductor.
Gases are poor conductors of electricity because the atoms ormolecules are usually too far apart to allow a free exchange ofelectrons.
INSULATORS
An insulator prevents electrical currents from flowing.Most gases are good electrical insulators.
Pure water is a good electrical insulator, although it conductssome current with even the slightest impurity.
IONIZATION
Ionization takes place when electrical insulators areforced to carry current.
DIELECTRIC
An insulating material is sometimes called a dielectric. It keeps electrical charges apart, preventing the flow of
electrons that would equalize a charge differencebetween two places.
Porcelain or glass can be used in electrical systems to keep short
circuits from occurring.
RESISTORS
Allow for the control of current flow. Electrical resistance is measured in units called ohms. The greater the resistance, the more difficult it
becomes for current to flow.
In an electrical system, it is usually desirable to have as low aresistance, or ohmic value, as possible. This is because resistanceconverts electrical energy into heat.
SEMICONDUCTORS
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In a semiconductor, electrons flow, but not as well as
they do in a conductor. Semiconductors are not exactly the same as resistors,
the material is treated so that i t has very specialproperties.
HOLE
A shortage of an electron. Holes move in the opposite direction from electrons in a
semiconducting material. When most of the charge carriers are electrons, thesemiconductor is called N-type, because electrons arenegatively charged.
When most of the charge carriers are holes, thesemiconducting material is known as P-type becauseholes have a positive electric charge.
The more abundant type of charge carrier is called themajority carrier.
The less abundant kind is known as the minority carrier .
CURRENT
Whenever there is movement of charge carriers in asubstance, there is an electric current.
Current is measured in terms of the number of electronsor holes passing a single point in one second.
A coulomb is equal to approximately6,240,000,000,000,000,000 electrons or holes.
*six quintillion ( 6 followed by 18 zeroes* quadrillions (numbers followed by 15 zeroes)
AMPERE
The standard unit of electric current. Current of one coulomb per second is called an
ampere.
STATIC ELECTRICITY
An excess or shortage of electrons is created on and inyour body. You acquire a charge of static electricity.
Its called static because it doesnt go anywhere.You dont feel this until you touch some metallic objectthat is connected to earth ground or to some largefixture; but then there is a discharge, accompanied bya spark.
Van de Graaff generator is a machine that an create a chargebuildup large enough to produce a spark several centimeterslong.
ELECTROMOTIVE FORCE
When the charge builds up, with positive polarity (shortage ofelectrons) in one place and negative polarity (excess ofelectrons) in another place, a powerful electromotive forceexists.
It is often abbreviated EMF. This force is measured in units calledvolts .
Ordinary household electricity has an effective voltage ofbetween 110 and 130; usually it is about 117. A car battery hasan EMF of 12 volts (six volts in some older systems).
An EMF of 1 volt, across a resistance of 1 ohm, will cause acurrent of 1 ampere to flow. This is a classic relationship inelectricity, and is stated generally as Ohms Law.
Voltage, or EMF, is sometimes called potential or potentialdifference.
VISIBLE LIGHT
Converts electricity into radiant energy that you can
see.
PHOTOVOLTAIC CELL
Visible light is converted into electric current orvoltage.
HEAT
A form of radiant energy called infrared. It is similar tovisible light, except that the waves are longer and youcant see them.
Electricity can also be converted into other radiant-energyforms, such as radio waves, ul traviolet, and X rays.
Generator
When a conductor moves in a magnetic field, electriccurrent flows in the conductor.
Converts mechanical energy into electricity.
Motor
Changes electricity into useful mechanical energy.
MAGNETISM
The science of magnetism is closely related toelectricity.
Magnetic phenomena are of great significance inelectronics.
The oldest and most universal source of magnetism isthe flux field surrounding the earth, caused byalignment of iron atoms in the core of the planet.
ELECTROMAGNETISM
A changing magnetic field creates a fluctuatingelectric field, and a fluctuating electric field producesa changing magnetic field.
CHEMICAL ENERGY
Converted into electricity in all dry cells, wet cells, andbatteries.
Your car battery is an excellent example. The acidreacts with the metal electrodes to generate anelectromotive force.
CHARGING
Then it runs out of juice, and the supply of chemicalenergy must be restored by charging.
Some cells and batteries, such as lead-acid carbatteries, can be recharged by driving current throughthem, and others, such as most flashlight and transistor-radio batteries, cannot.
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CHAPTER 2: ELECTRICAL UNITS
VOLT
Standard unit of electromotive force (EMF) or potentialdifference.
Potential difference between two points produces anelectric field, represented by electric lines of flux. (pole thatis relatively positive with fewer electrons and negative polewith more electrons)(p.18 fig2-1)
Abbreviation for volt is V. Dry cell voltage = 1.2 1.7 volts
Car battery = 12 14 voltsElectric lights = 117 voltsWashing machine, dryer, oven, stove = 234 volts
Largest voltages on our planet occur between clouds andthe ground, in thunderstorms.
Existence of voltage always means that charge carriers,which are electrons(e-) in a conventional circuit, flowbetween two points if a conductive path is provided.Voltage represents the driving force that impels chargecarriers to move.
CURRENT FLOW
It is the flow of electrons (e-). The flow of e- to equalize thecharge between poles.
It is the current , not the voltage that kills. There can only bea deadly current if there is enough voltage to drive itthrough your body.
Standard unit for current is Ampere. The amount of current that flows in an electrical circuit
depends on the voltage and also on the resistance (V=IR)
RESISTANCE
The measure of opposition that a circuit offers to the flow ofelectric current.
Ohms Law (V=IR) = current flow for a constant voltage issaid to be inversely proportional to the resistance.
CONDUCTANCE & SIEMENS
It is the reciprocal of resistance Unit is S for Siemens
G = 1/RR = 1/G1k ohm = 1m S1M ohm = 1uS
POWER AND THE WATTS
Whenever current flows through a resistance, heat results.Heat can be measured in watts(W) and representselectrical power.
P = EIP = VI
I = P/VV = P/I
ENERGY AND WATT-HOUR
Energy is power dissipated over a length of time Power is the rate at which energy is expended.
ENERGY UNITS
Mostly used is joules Page 27 Figure 2-3
In terms of joules:British thermal unit (Btu) = 1055Electron volts (eV) = 1.6X10 -19 Ergs = 0.0000001 / 10 -7 Foot-pounds(ft-lb) = 1.356Watt-hours = 3600Kilowatt- hours= 3,600,000 / 3.6x10 -6
ALTERNATING CURRENT AND HERTZ
Effective voltage for an ac wave is never the same as theinstantaneous maximum, or peak voltage. (p.28 fig.2-8)
Effective value is 0.70707 times the peak value. Or 1.414times the effective value
The instantaneous voltage is the voltage at any particularinstant in time.
Whole cycle repeats itself every 1/60 second, the
frequency of the utility ac wave is said to be 60 hertz Hertz literally translate to cycles per second
RECTIFICATION AND PULSATING DIRECT CURRENT
Rectification is a process in which ac is changed to dc Common method of doing this uses a device called the
diode. The point is that part of the ac wave is either cut off, or
turned around upside down, so the output is pulsating dc. There are two different forms of waveforms of pulsating dc.
(refer to p.29 fig 2-10).1. Half wave rectification2. Full wave rectification
Peak voltage is the maximum instantaneous voltage. Instantaneous voltage is never any greater than the peak
voltage for any wave.
MAGNETISM
Electric current and magnetic fields are closely related. When an electric current flows which i s when charge
carriers move a magnetic field accompanies thecurrent.(p.30 fig 2-11)
Magnetic fields are produced when the atoms of certainmaterials align themselves. Iron is the most common metalthat has this property.
The intensity of a magnetic field can be greatly increasedby placing a special core inside of a coil. Should be of ironor some other material that can be readily magnetized,such substance are ferromagnetic.
A core of this kind cannot actually increase the totalquantity of magnetism in and around a coil, but i t will
cause the lines of flux to be much closer together inside thematerial. Magnetic flux of lines are said to emerge from the
magnetic pole, and to run i nward toward the magneticsouth pole.
MAGNETIC UNITS
Overall magnitude of a magnetic field i s measured in unitscalled Webers(Wb)1 weber = 1 volt-second( 1 Vs)
For weaker magnetic fields, a smaller unit calledmaxweel(Mx) is used.
1 maxwell = 0.00000001 (1 hundredmillionth) of a weber or 0.01microvolt-second( 0.01uVs)
Flux density of a magnetic field is given in terms of webersor maxwells per square meter or per square centimeter.1 Wb/m 2 is called Tesla (1T)1 Mx/cm 2 is called gauss (1G, 0.0001 T)
As the electric current through a wire increases, so doesthe flux density near the wire.
A coiled wire produces a greater flux density for a givencurrent than a single, straight wire.
The more turns in the coil, the stronger the magnetic fieldwill be.
A magnetic field strength maybe specified in terms ofampere-turns (At). Unit of a magnetomotive force.
One loop carrying 1A of current, produces a field of 1 At. Doubling the number of turns, or the current, doubles the
number of ampere-turns.
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Less common unit of magnetomotive force is gilbert(Gb).This unit is equivalent of 0.796 At. 1 At=1.26 Gb
CHAPTER 3: MEASURING DEVICES
* Galvanometer * Electroscope * Ammeter (milli, micro) * Electrostatic meter * Voltmeter * Ohmmeter * Multimeter * FET voltmeter
* Wattmeter * Watt-hour meter * Frequency Counter * VU meter * light meter * Oscilloscope
A galvanometer is a type of ammeter: an instrument fordetecting and measuring electric current.
Galvanism -it is the induction of electrical current
Eletroscope - The most common device for demonstratingelectrostatic force
Ammeter - is a measuring instrument used to measure theelectric current in a circuit. ( It i s placed in series with one ofthe device on the circuit)
Electrostatic meter - Can detect ac as well as dc voltages
voltmeter - is an instrument used for measuring theelectrical potential difference between two points in anelectric circuit (Place in parallel)
* Voltmeter should have a high internal resistance *
FET voltmeter - It draws less current from the circuit
Multimeter - also known as a volt/ohm meter or VOM, is anelectronic measuring instrument that combines severalmeasurement functions in one unit. A typical multimetermay include features such as the ability to measure
voltage, current and resistance. Wattmeter - The wattmeter is an instrument for measuring
the electric power (or the supply rate of electrical energy)in watts of any given circuit.
Watt-hour meter - is a device that measures the amount ofelectrical energy consumed by a residence, business, oran electrically-powered device.
Frequency Counter - i s an electronic instrument, orcomponent of one, that is used for measuring frequency.
VU meter - is often included in audio equipment to displaya signal l evel in Volume Units; the device i s sometimes alsocalled volume indicator (VI).
light meter - is a device used to measure the amount oflight. also known as illumination meter.
Oscilloscope - is a type of electronic test instrument thatallows signal voltages to be viewed, usually as a two-dimensional graph of one or more electrical potentialdifferences (vertical(Y) axis) plotted as a function of timeor of some other voltage (horizontal(x) axis).
Hot wire ammeter - A device capable of measuring ac.dccurrents
D'arsonval movement - An action caused byelectromagnetic deflection, using a coil of wire and amagnetized field. When current passes through the coil, aneedle is deflected.
In a simple ammeter, an electromagnet can be useinstead of permanent magnet
A resitor is connected across the ammeter if it is necessaryto measure very large amount of current. also known asshunt resistance or meter shunt.
"Dont leave voltmeter constantly connected to the circuit",it will affect the behavior of the circuit due to the resistanceof the voltmeter.
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CHAPTER 4: BASIC DC CIRCUITS
Wiring Diagram is more detailed than Schematic
Voltage/Current/Resistance Circuit Calculations
Ohms Law triangle.
NOTE: Wag kalimutang i-take into consideration ang mga PREFIX!
Power Calculations
Resistances in series : Add directly!
Resistance in Parallel: Get the ReciprocalAdd
Get the Reciprocal Again
For Parallel Resistors having the same values , just divide one value bythe number of resistors.
Example: May 4 resistors connected in parallel each having a value5 k . Total resistance = 5 k 4 = 1.250 k
Division of Power
Total Power Load = Evenly distributed among theresistances of the circuit if they have the same ohmicvalues .
Construction of Series Parallel Matrix (Resistances)-To increase the power handling capacity
Conditions to consider :--Identical resistors should be used!--(n) x (n) x (power rating) = total power capacity--Consider the resistances youre going to need i.e. #18 -- Most likely n x n is better than n x m due to resistance issues i.e.
#17
Chapter 5: Direct-Current Circuit Analysis
Ohms Law: V = IR Power, P = VI
Current through Series Resistances*The current in a series circuit is the same at every pointalong the way.
Voltages across Series Resistances*The voltages across elements in a series circuit always addup to the supply voltage.
Voltage across Parallel Resistances*In a parallel circuit, the voltage across each component isalways the same and it is always equal to the supply orbattery voltage.
Currents through Parallel Resistances*The currents through elements in a parallel circuit alwaysadd up to the total current drawn from the supply.
Conventional/Theoretical Current Flow
*Current flows from the positive to the negative voltagepoint.
Power Distribution in Series CircuitsP = I2RPower Distribution in Parallel CircuitsP = V 2/R
*The total power consumed in a series or parallel circuit is alwaysequal to the sum of the wattages dissipated in each of the elements.
Kirchhoffs First Law (Kirchhoffs Current Law, KCL) *Conservation of Current: At any node (junction) in anelectrical circuit, the sum of currents flowing into that nodeis equal to the sum of currents flowing out of that node.
Kirchhoffs Second Law (Kirchhoffs Voltage Law, KVL) *Conservation of Voltage: The sum of the EMFs in anyclosed loop is equivalent to the sum of the potential dropsin that loop.
Voltage Divider Networks*The voltage divider fixes the intermediate voltages bestwhen the resistance values are as small as the current-delivering capability of the power supply will allow.
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CHAPTER 6: RESISTORS
PURPOSE OF THE RESISTOR:
1. Voltage Division
The resistors dissipate some power but the resultingvoltages can provide the proper biasing of electronic
circuits. For example, an amplifier or oscillator will function inthe most efficient and reliable way possible.
2. Bias
Bias, in the case of bipolar transistor, a field-effecttransistor or a vacuum tube, that the controlelectrode - the bias, gate or grid is provided with acertain voltage, or carry a certain current, relative tothe emitter, source or cathode.
3. Current Limiting
Resistors interfere with the flow of electrons in a circuit. This is essential to prevent damage to a component or
circuit. A good example is in a receiving amplifier. A resistor
can keep the transistor from using up a lot of power just getting hot.
4. Power Dissipation
In radio, a resistor can be used to take the place of anantenna. A transmitter can then be tested in such away that it doesnt interfere with signals on theairwaves. The transmitter output heats the resistor,without radiating any signal.
The circuit driving the amplifier has too much power
for the amplifier input. A resistor, or network of resistors,can dissipate this excess so that the power amplifierdoesnt get too much drive.
5. Bleeding Off Charge
Bleeder resistors, connected across the filtercapacitors, drain their stored charge so that servicingthe supply is not dangerous.
6. Impedance Matching
In order to produce the greatest possibleamplification, the impedances must agree betweenthe output of a given amplifier and the input of thenext.
FIXED RESISTORS
Units whose resistance does not change, or cannot beadjusted.
1. Carbon-Composition Resistors
Carbon-composition resistors can be made to havequite low resistances, all the way up to extremely highresistances.
Nonreactive - introduces almost pure resistance intothe circuit, and not much capacitance orinductance.
Useful in radio receivers and transmitters.
Most of the carbon-composition resistors can handle 14 W or 1/2 W.
2. Wirewound Resistors
The resistance is determined by how well the wiremetal conducts, by its diameter or gauge, and by itsstretched-out length.
Precision Components. Can handle large amount of power. Disadvantage: Act like inductors. Low moderate Values of resistance.
3. Film-Type Resistors Metal-film resistors can be
made to have nearly exactvalues.
Low to medium resistance. Advantage: Do not much
have inductance orcapacitance.
Disadvantage: Cant handle as much power ascarbon-composition or wirewound types.
4. Integrated-Circuit (IC) Resistors Resistors can be fabricated on a semiconductor
wafer known as an IC also called a chip.
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Can handle only a tiny amount of powerbecause of their small size.
THE POTENTIOMETER
1. Linear-Taper Potentiometer
One type of potentiometer uses a strip of resistive materialwhose density is constant all the way around.
The resistance between the center and one end terminalwill increase right along with the number of angulardegrees that the shaft is turned.
Linear taper potentiometers are commonly used inelectronic test instruments and in various consumerelectronic devices.
2. Audio-Taper Potentiometer
The resistance between the center and the end terminalincreases as a nonlinear function of the angular shaftposition.
Also called logarithmic-taper potentiometer or log-taperpotentiometer.
3.
The Rheostat A variable resistor made from a wire wound element. Either have a rotary control or a sliding control. Rheostat can be placed between the utility outlet and the
transformer. This results in a variable voltage at the power-supply output.
THE DECIBEL
RESISTORS SPECIFICATIONS
Ohmic Value
Tolerance
Power Rating Temperature Compensation The Color Code for Resistors
dB= 10 log (Q/P)Q = P antilog (dB/10)
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CHAPTER 7: CELLS AND BATTERIES
CELL a unit source of DC energy.
BATTERY two or more cells connected in series.
ELECTROCHEMICAL ENERGY
Voltages appeared between pieces of metal whencame into contact with certain chemical solutions.
Chemicals and the metals have an inherent ability to
produce a constant exchange of charge carriers. Note: The chemical energy in a battery or cell changes
to electrical energy when the cell is used.
PRIMARY CELLS
electrical cells which chemical energy has all beenchanged to electricity and used up must be thrownaway and cannot be recharged.
i.e. batteries used in flashlight or transistor radio; AAAbatteries, D batteries, watch and camera batteries, 6-Vlantern batteries [dry cell, zinc-carbon cell or alkalinecell]
SECONDARY CELLS
cells that can get chemical energy back by means of recharging.
i.e. A, C or D batteries, car batteries [nickel-based cells]
WESTON STANDARD CELL
produces 1.018V at room temperature. *generally used as voltage reference source
STORAGE CAPACITY
Ampere-hours (Ah) unit of electrical energy in a cell. Shelf life length of time the battery will last if it is never
used. Maximum deliverable current highest amount of
current that the battery can provide before its voltagedrops because of its own internal resistance .
Small cells: 100-200 mAh Medium-sized cells: 500 mAh to 1Ah Large automotive or truck batteries: 50Ah and up **A direct short-circuit of a large battery can cause a
physical rupture or explosion.
Note: The energy in a cell or battery depends mainly onits physical size .
AAA very small AA small C medium large D large
ZINC-CARBON CELLS
Inexpensive good at moderate temperature and not very good in
extreme cold good in applications where the current drain is
moderate to high
ALKALINE CELLS
can work at lower temperatures than a zinc-carboncell
lasts longer in most electronic devices preferred for use in transistor radios, calculators and
portable cassette players
shelf life is much longer than zinc-carbon costs more
TRANSISTOR BATTERIES
consists of 6 zinc-carbon or alkaline cells in series thatsupplies 1.5V each. Thus, the battery supplies 9V.
used in low-current electronic devices preferred for use in remote-control garage door
openers, TV and hi-fi remote controls and electroniccalculators
*The voltage produced by a battery of multiple cellsconnected in series is more than the voltage producedby a cell of the same composition.
LANTERN BATTERIES
has much greater mass than a common dry cell ortransistor battery
lasts much longer deliver more current usually rated 6V good for scanner radio receivers in portable
locations(two-way portable radio), camping lamps,and other medium-power needs
MINIATURE CELLS AND BATTERIES
used in wristwatches, small cameras, and variousminiature electronic devices
SILVER-OXIDE CELLS AND BATTERIES
buttonlike shape and can fit inside a small wristwatch cells supply 1.5V cells can be stacked up to make batteries that can
provide 6, 9 or 12V used for transistor radio and other light-duty electronic
devices
MERCURY CELLS AND BATTERIES
properties similar to silver-oxide cells supply 1.35V when dead, they must be discarded because mercury
is toxic to human and animals
LITHIUM CELLS AND BATTERIES
cells supply 1.5-3.5V used for memory backup for electronic
microcomputers, LCD watch or clock have superior shelf life; can last for years in very low
current applications
LEAD-ACID BATTERIES
rechargeable
used in consumer electronic devices that requiremoderate amount of current
ie. Uninterruptible power supply (UPS) that can keep aPC running for a few mins when power fails
automotive battery is a large lead-acid battery not expensive
NICKEL-BASED CELLS AND BATTERIES
rechargeable cylindrical cells ordinary dry cells button cells used in watches, cameras, memory
backup flooded cells used in heavy-duty applications; storage
capacity in excess of 1000Ah
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spacecraft cells **Never discharge nickel-based cells all the way until
they totally die
PHOTOVOLTAIC CELLS AND BATTERIES
converts visible light, infrared (IR) and/or ultraviolet (UV)directly into electric current
SOLAR PANELS
photovoltaic cells combined in series-parallel often very large; consist of 50x20 cells
series scheme boosts the voltage to desired level parallel scheme increases the current-delivering ability
of the panel used in satellites can be used in conjunction with rechargeable
batteries to provide power in commercial utilities interactive solar system allows a homeowner to sell
power to the electric company
FUEL CELLS
HYDROGEN FUEL
hydrogen combined with oxygen hydrogen oxidizes at a lower temperature proton exchange membrane (PEM) is widely used and
generates approximately 0.7Vdc
METHANOL
advantage of being easier to transport and store thanhydrogen
PROPANE
stored in liquid in tanks; used in heating system METHANE natural gas
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CHAPTER 8: MAGNETISM
Geomagnetic Field
earths core made up of iron and has poles.
North geomagnetic pole
located far northern Canada
South geomagnetic pole
located near Antarctica
Geomagnetic axis
relative to the axis on w/c earth rotates.
Solar wind
stream of particles from the sun that distort thegeomagnetic lines of flux (sun ejects protons & heliumnuclei constantly which is a positive electric charge)Fig. 8-1
Lode stones
rock used in ancient times as a navigating tool
Magnetic compass
needle tries to align parallel to the lines of flux
*geomagnetic inclination and geomagnetic declination
Ferromagnetic material
(iron,nickel & alloys) stick to magnets and can bepermanent magnets.
Magnetic force
magnet is brought near a ferromagnetic material,atoms lined-up and the material temporarilymagnetized
Attraction and repulsion
force gets stronger as the magnets are brought neareach other.
Magnetic field
occurs when ferromagnetic materials are aligned;caused by the motion of electric charge carriers, eitherin wire or free space.
Solar flare
sun ejects far more charged particles than normal anddisrupts the geomagnetic field.
Geomagnetic storm
disruption of geomagnetic field w/c causes the earthsionosphere to change and affect long distance radiocomm. At certain frequency
Flux lines
determines the intensity of a magnetic field*bar magnet- N to S Fig. 8-2*current-carrying wire- circles around the wire Fig. 8-3
Electric monopole
a charged particle, such as proto or electron hoveringall by itself in space
Electric lines of flux
charged particle in free space are straight and run offto infinity Fig. 8-4
Magnetic dipole a pair of magnetic poles
Magnetic field strength
Webers(Wb) *strong; Maxwell(Mx) *weak
1Wb = 10 8Mx ; 1Mx = 10 -8 Mx
Tesla and gauss
concentration or intensity of magnetic field w/ in acertain cross section
Flux density
no. Of lines per square meter or per square cm
1Tesla(T) = 1Wb/m 2 ; 1Gauss(G) = 1Mx/cm 2 1G = 10 -4 T ; 1T = 10 4G
Ampere-turn(At)
unit of magnetomotive force and counterpart of emf
1Gb = 0.796At ; 1At = 1.26Gb
Electromagnet
type of magnet which produces a magnetic field with
the use of electric current *DC types- large bolt wrapping a few dozen of wirearound it with a battery to provide current Fig. 8-5
*AC types- wall outlet as a source; magneticlevitationFig. 8-6
Magnetic Properties of Materials
1.Ferromagnetism
when substance cause magnetic lines of flux to bunchcloser together.
2.Diamagnetism
when substance decreases the magnetic flux densityby causing the magnetic flux to diverge.
3.Permeability
indicator of extent to w/c a ferromagnetic materialconcentrates magnetic lines of flux.
4.Retentivity
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also called remanence; is a measure of how well thesubstance memorizes the magneti sm and becomesa permanent magnet.
Br= 100(y/x)% (y- current removed; x- current subjected)
Practical Magnetism
1. Permanent Magnets
manufactured using a high-retentivity ferromagnetic
material.
2. Ringer Device
bell ringer or chime Fig. 8-7 main component called solenoid
3. Relay
remote control switching of high current circuits Fig. 8-8
4. DC motor
converts DC energy to rotating mechanical energy attraction of opposite pole and repulsion of like poles;
constant torque Fig. 8-9
Armature coil set of coils rotate w/ the motor shaft
Field coil- stationary
Commutator
keeps the rotational force going in the same angulardirection to rotate not to oscillate.
5. Magnetic Tape
recording head which polarizes the ferro-particles
6. Magnetic Disks
hard drives which stores the most data, found insidethe computer
7. Bubbling Memory
sophisticated method of storing data a type of non-volatile computer memory that uses a
thin film of a magnetic material to hold smallmagnetized areas, known as bubbles or domains ,each of which stores one bit of data.
http://en.wikipedia.org/wiki/Non-volatile_memoryhttp://en.wikipedia.org/wiki/Computer_memoryhttp://en.wikipedia.org/wiki/Bithttp://en.wikipedia.org/wiki/Bithttp://en.wikipedia.org/wiki/Computer_memoryhttp://en.wikipedia.org/wiki/Non-volatile_memory8/10/2019 Complete Gibilisco
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CHAPTER 9: ALTERNATING CURRENT
Characteristics of AC
1. polarity reverses again and again at regular intervals. 2. Amplitude varies 3. Frequemcy-dependent
PERIOD AND FREQUENCY
PERIOD (T)
the length of time between one repetition of thepattern, or one cycle, and the next
FREQUENCY(f)
cycles per second (cps)Hertz(Hz)1 cps = 1 Hz
Relationship between Period and Frequency
Pure
ac waves that have only one frequency
Fundamental: ac waves that have components atmultiples of the main.
THE SINE WAVE
Sine wave means that the direction of the currentreverses at regular intervals
current-versus time curve is shaped like thetrigonometric sine function.
SQUARE WAVES
an AC wave whose instantaneous amplitude remainsconstant even though the polarity reverses.
ASYMMETRICAL SQUARE WAVES
squared off wave that are lopsided.
SAWTOOTH WAVES
ac waves that rise and fall in straight lines as seen on anoscilloscope screen
Slope
indicates how fast the magnitude is changing
Three kinds of Sawtooth Waves
1. Fast-rise, slow-decay - The positive-going slope (rise) isextremely steep, as with a square wave, but thenegative-going slope (fall or decay) is gradual .
2. Slow-rise, fast-decay - sometimes called a ramp ,because it looks like an incline going upwards. It isuseful for scanning in television sets and oscilloscopes
3. Variable rise and decay - slopes in an infinite numberof different combinations.
Complex and irregular waveforms
As long as it has a definite period, and as long as thepolarity keeps switching back and forth betweenpositive and negative, it is ac.
Frequency spectrum
Oscilloscope
time domain instrument
Spectrum analyzer
frequency-domain instrument
Pure sine wave
single pip
Fundamental: contains harmonic energy along withenergy at the fundamental frequency.
FRACTIONS OF A CYCLE
1 cycle = 1 rev around a circle
Degrees
One method of specifying the phase of an ac cycle isto divide it into 360 equal parts, called degrees ordegrees of phase.
Starts at 0 where magnitude is zero and positive-goingand ends at 360.
Radians
A cycle can be divided into equal parts. 1 rad phase = rad = the angular frequency of a wave, in radians per
second, is equal to about 6.28 times the frequency inhertz.
PHASE DIFFERENCE
Composite wave produced by adding ac waves together
frequency amplitude phase Compositeoutput
identical identical Differ by180
Does not exist
identical Identical In phase Samefrequency;amplitude =twiceamplitude of
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either signalidentical Different Differ by
180Samefrequency;amplitude =differencebetween thetwo
identical Different identical Samefrequency;amplitude =sum betweenthe two
identical Different Differ byoddamount
Samefrequency;variety isinfinite
EXPRESSIONS OF AMPLITUDE
Amplitude
magnitude level, strength or intensity
Instantaneous amplitude
the amplitude at some precise moment in time. constantly changes
Peak amplitude
the maximum extent, either positive or negative, thatthe instantaneous amplitude attains.
Peak-to-peak amplitude
the net difference between the positive peakamplitude and the negative peak amplitude.
Root-mean-square amplitude
It literally means that the value of a wave ismathematically operated on, by taking the square rootof the mean of the square of all its values
Effective level of an ac wave
is the voltage, current or power that a dc source wouldhave to produce, in order to have the same generaleffect.
For a perfect sine wave,
rms value = 0.707 x peak value, or= 0.354 x pk-pk value
peak value = 1.414 x rms value pk-pk value = 2.828 x rms value
For a perfect square wave,
rms value = peak value pk-pk value = 2 x rms value or the peak value
Superimposed direct current
Sometimes a wave can have components of both acand dc
If the dc component exceeds the peak value of the acwave, then fluctuating, or pulsating, dc will result
THE GENERATOR
The ac voltage that a generator can develop dependson the strength of the magnet, the number of turns in
the wire coil, and the speed at which the magnet orcoil rotates.
The ac frequency depends only on the speed ofrotation.
for utility ac, this speed is 3,600 revolutions per minute(rpm), or 60 complete revolutions per second (rps), sothat the frequency is 60 Hz.
The efficiency of a generator is the ratio of the poweroutput to the driving power, both measured in thesame units multiplied by 100 to get a percentage.
Why AC?
Alternating current lends itself well to being transformedto lower or higher voltages, according to the needs ofelectrical apparatus
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CHAPTER 10: INDUCTANCE
INDUCTORS
electrical components that oppose the flow of AC bytemporarily storing energy as magnetic fields .
INDUCTANCE, L
directly proportional to the number of turns in a wire,and diameter and length of a coil
1H represents a potential difference of 1V across aninductor which the current is changing at the rate of1A/s
*Small coils w/ few turns of wire produce smallinductances, in which the current changes quickly
*Large coils w/ ferromagnetic cores and having manyturns of wire, current changes slowly
INDUCTORS IN SERIES
L = L1+L 2+L3++L n
INDUCTORS IN PARALLEL
1/L =1/ L 1+1/L 2+1/L 3++1/L n
COEEFICIENT OF COUPLING, k
ranges 0 (no interaction) to 1 (maximum possibleinteraction)
k=0 when two coils are separated by a sheet of solidiron or by a great distance
k=1 when two coils wound on the same form, one rightover the other
MUTUAL INDUCTANCE, M
M= k (L1L 2 )1/2
if two ac waves are in phase, the inductance isincreased
it two waves are in opposing phase the inductance isdecreased
*When two inductors are connected in series and there isreinforcing mutual inductance between them
L = L1+L 2+2M
* When two inductors are connected in series and there isopposing mutual inductance between them
L = L1+L 2-2M
AIR-CORE COILS
excellent efficiency used mostly in radio-frequency transmitters, receivers
and antenna networks *the higher the frequency of ac, the less inductance is
needed to produce significant effects By using heavy-gauge wire and making the radius of
the coil large, air-core coils have almost unlimitedcurrent-carrying capacity
disadvantage: low permeability
FERROMAGNETIC CORES
common at high and very high radio frequencies used at audio frequencies, as well as at low, medium
and high radio frequencies
has high permeability, causing a great concentrationof magnetic flux lines within the coil
smaller than air-core coils disadvantage: has potential for the core to saturate;
when a core becomes saturated, any further increasein coil current will not produce a correspondingincrease in the magnetic flux in the core
can also waste considerable power as heat making thecoil lossy
SOLENOIDAL COILS
used in adjusting frequency of a radio circuit can be made to have a variable inductance by sliding
ferromagnetic cores in and out of them controlled by ascrew shaft
moving the core further in the solenoidal coil increasesthe inductance
TOROIDS
advantage: fewer turns of wire are needed to get acertain inductance
: physically smaller for a given inductance and current-carrying capacity
: all the flux is contained within the core material reduces unwanted mutual inductances
disadvantage: difficult to permeability-tune : harder to wind : mutual inductance between or among physically
separate coils is actually desired
POT CORES
same advantages as toroids better than toroids if the main objective is to get a
large inductance in a small space disadvantage: tuning or adjustment of inductance is
impossible
FILTER CHOKES
large coil used to smooth out the pulsations in directcurrent that result when ac is rectified in a power supply
INDUCTORS AT AF
range in value of a few millihenrys up to about 1H
INDUCTORS AT RF
ranges from a few kilohertz to well above 100 Ghz. as the frequency increases, cores having lower
permeability are used
TRANSMISSION LINE INDUCTORS
used to get energy from one place to another
used at frequencies about 100Mhz
LINE INDUCTANCE
Scm =7500v/f
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CHAPTER 11: CAPACITANCE
Capacitance
impedes the flow of ac charge carriers by temporarystoring the energy as an electric field
Property of Capacitance
Fig. 11-1 the size of the plate has a major factor; Fig. 11- 2 capacitor charge over a period of time
*Capacitance is directly proportional to the surfacearea of the conducting plates or sheets, and inverselyto the separation between conducting sheets
*the closer the sheets are to each other, the greaterthe capacitance
Unit of capacitance - ratio between the current thatflows and the rate of voltage change between theplates as the plate become charged
1 farad(1F)o - 1A while there is a voltage increase 1V/so 1V potential difference for an electric charge
of 1C.1 F = 10 -6 F ; 1 pF = 10 -12 F
Capacitors in Series:
1/C = 1/C 1 + 1/C 2 + 1/C 3 + . . . + 1/C n *net capacitance is roughly equal to the smallest
capacitance
If C1 = C 2 = C 3 = ... = C n ; C = C 1/n
Capacitors in Parallel:
C = C1 + C2 + C3 + ... + C n
Fixed Capacitors
has a value that cannot be adjusted and does not varywhen environmental or circuit conditions change
Dielectric materials
accommodate electric fields well, but poor conductorsof electric currents
good insulators Fig. 11-5
Paper Capacitors
placing a paper soaked w/ mineral oil between stripsof foil.
ranging about 0.001 F to 0.1F ; low to moderatevoltages up to about 1000V
Mica Capacitors
alternately stacking metal sheets & layers of mica Fig.11-6; main application for radio receiver andtransmitter
ranging little lower than paper capacitors ranging fromfew tens of pF up to 0.05F
Ceramic Capacitors
meshing & layering like mica, ranging from few pF toabout 0.5F ; voltage comparable to paper capacitors
disk ceramic capacitor- for small values only one layerof ceramic is needed & 2 metal plates glued to the diskshaped material on each side.
tubular capacitors- tube or cylinder of ceramics can beinside & outside of tube
Plastic-Film Capacitors plastics make good dielectrics for capacitors polyethylene & polystyrene are used, manufactured
same as paper capacitors range from 50pF to several tens of F , most often at
0.001F to 10F
Electrolytic Capacitors
provides greater capacitance, polarized component can have thousands of F & can handle thousands of
volts
Tantalum Capacitors
replacement for aluminium; used in militaryapplications because they almost never fail.
electrolytic capacitor
Semiconductor Capacitors
embedded on an IC or chips Fig. 11-7
Semiconductor Diode
conducts current in one direction, & refuse to conductin the other direction
*when a voltage source is connected across a diode so that it does not conduct, the diode acts as acapacitor.
*the greater the reverse voltage, the smaller thecapacitance
Variable Capacitors
adjusting the mutual surface area between the plates changing the spacing between the plates
Air Variables
connecting 2 sets of metal plates so that they mesh,and by affixing one set to a rotable shaft, Fig. 11-8
max capacitance depends on the no. Of plates &spacing between plates
common values 50-500pF
Trimmer Capacitors Fig. 11-9 few pF up to about 200pF
Coaxial Capacitors
TL < /4 acts as a capacitor. Capacitance increaseswith length Fig. 11-10
Capacitor Specifications
1. Tolerance
the lower the tolerance no. The more closely youexpect the actual component value to match therated value
2. Temperature Coefficient (%/ oC)
Positive temp. Coefficient - increase in value as thetemperature rises
Negative temp. Coefficient - decrease in value as thetemperature rises
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Zero temp. Coefficient - value remain constant within aspan of temperature
Interelectrode Capacitance
when two piece of conducting material are broughtnear each other
CHAPTER 12: PHASE
INSTANTANEOUS VALUES
+1V positive peak; negative going-1V negative peak; positive going
INSTANTANEOUS RATE OF CHANGE
The Graph 12.2 is the instantaneous rate of change of asine wave but is 1/4 phase difference than the originalsine wave, that makes is cosine.
VECTOR
Is a quantity with two independent properties calledmagnitude (amplitude) and direction .
Amplitude is independent of time. The vector lengthnever changes but its direction does.
PHASE DIFFERENCE
Also called phase angle . The Phase differencebetween two waves can have meaning only when twowaves have identical frequencies.
PHASE COINCIDENCE
Two waves begin at exactly the same moment but ofdifferent amplitudes.
Phase difference in this case is 0.
If two sine waves are in phase coincidence, the peakamplitude of the resultant wave, which will also be asine wave, is equal to the sum of the peak amplitudesof the two composite waves.
The phase of the resultant is the same as that of thecomposite waves.
PHASE OPPOSITION
Two waves begin exactly 180 apart.
INTERMEDIATE PHASE DIFFERENCE
0 and 360 phase coincidence 90 and 270 quadrature 180 phase opposition
LEADING
If wave X begins a fraction of a cycle earlier than waveY, then wave X is said to be leading wave Y in phase.
LAGGING
Imagine that wave X starts its cycle later than wave Y, by somevalue between 0 and 180 degrees. Then wave X is lagging,wave Y.
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VECTOR DIAGRAMS OF PHASE DIFFERENCE
TIME Is represented by counterclockwise motion of both
vectors at constant angular speed.
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CHAPTER 14: CAPACITIVE REACTANCE
The capacitive-reactance ray goes in a negativedirection and is assigned negative ohmic values.
Capacitors
Capacitive reactance, like inductive reactance,varies with frequency. But X C gets LARGER(negatively) as the frequency goes down.
Capacitive reactance is talked about in terms of i tsabsolute value, with minus sign removed.
The absolute value of X C increases as the frequencygoes down, or that the absolute value of X Cdecreases as the frequency goes up.
Capacitive Reactance and Frequency
Current Leads Voltage
In a circuit containing capacitive reactance, thevoltage lags the current in phase. Thus, current leadsvoltage.
PURE CAPACITANCE
XC is extremely largecompared with theresistance R.
Current leads thevoltage by just about90 o
CAPACITANCEANDRESISTANCE
f R is
smallcomparedwiththeabsolu
te value of X C, the difference is almost a quarter of acycle. As R gets larger, or as the absolute value of X Cbecomes smaller, the phase difference decreases.
A circuit containing resistance and capacitance iscalled an RC Circuit.
PURE CAPACITANCE
The absolute value of the capacitivereactance gets small enough, the circuit actsas a pure resistance, and the current is inphase with the voltage.
XC = -1/(2 f C)XC = -1/(6.28 f C)
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CHAPTER 15: IMPEDANCE AND ADMITTANCE
ADMITTANCE
the extent to which an ac circuit allows current flow,rather than impeding it.
Imaginary numbers
i is the . It is the number that, when multiplied by itself,gives 1. So i = j, and j x j =1.
In electronics, real numbers represent resistances.Imaginary numbers represent reactances.
Complex numbers
This term doesnt mean complicated; it would betterbe called composite.
Adding and subtracting complex numbers
The general formula for the sum of two complexnumbers ( a + jb ) and ( c + jd ) is
(a + jb ) + ( c + jd ) = ( a + c ) + j(b +d )
Multiplying complex numbers
The product of ( a + jb ) and ( c + jd ) is equal to(a + jb )(c + jd ) = (ac - bd ) + j(ad + bc )
The complex number plane
Absolute value
The absolute value of a complex number a + jb is thelength, or magnitude, of its vector in the complexplane, measured from the origin (0,0) to the point ( a ,b).
In the case of a pure real number a + j0, the absolutevalue is simply the number itself, a .
In the case of a pure imaginary number 0 + jb, theabsolute value is equal to b.
If the number is neither pure real or pure imaginary:
The RX plane
Resistances are represented by nonnegative realnumbers. Reactances, whether they are inductive(positive) or capacitive (negative), correspond toimaginary numbers.
Capacitors act like negative inductors
Vector representation of impedance
Any impedance R + jX can be represented by acomplex number of the form a + jb. Just let R =a and X=b.
Resistance is one-dimensional. Reactance is also one-dimensional. But impedance is two-dimensional.
Absolute-value impedance
the capital letter Z is used in place of the wordimpedance
If youre not specifically told what complex impedanceis meant when a single number ohmic figure is quoted,its best to assume that the engineers are talking aboutnonreactive impedances.
Characteristic impedance Characteristic impedance or surge impedance. It is
abbreviated Zo, and is a specification of transmissionline
Transmission lines
is required any time that it is necessary to get energy orsignals from one place to another
take either of two forms, coaxial or two wire
Factors affecting Zo
of the wires, spacing between the wires, The nature of the insulating material separating the
wires. diameter In general, Zo increases as the wire diameter
gets smaller, and decreases as the wire diameter getslarger, all other things being equal.
In a coaxial line, the thicker the center conductor, thelower the Zo if the shield stays the same size. If thecenter conductor stays the same size and the shieldtubing increases in diameter, the Zo will increase.
Impedance Matching
Is the process of making sure that the impedance ofthe load is purely resistive, with an ohmic value equal tothe characteristic impedance of the transmission lineconnected to it.
Conductance (G)
works the same way as it does in a dc circuit.G=1/R
Susceptance (B)
It is the reciprocal of reactance Can be either capacitive or inductive
BC = 1/ XC, and BL = 1/X L 1/j = -j and 1/-j = j
Admittance (Y)
Conductance and susceptance combine to formadmittance.
a complex quantity and represents the ease with whichcurrent can flow in an ac circuit
As the absolute value of impedance gets larger, theabsolute value of admittance becomes smaller
negative j factors mean that there is a net inductancein the circuit, and
positive j factors mean there is net capacitance.
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CHAPTER 16: RLC AND GLC CIRCUIT ANALYSIS
RLC (Resistance-Inductance-Capacitance)
GLC (Conductance-Inductance-Capacitance)
RX (resistance-reactance) >> series ckt analysis
GB (conductance-admittance) >> parallel ckt analysis
Complex Impedances in Series
Z = (R1+R2) + j (X 1 + X 2)
Pure Reactances:
X = X L + X C
jXL = j2fL >> always positive jXC = - j / (2fC) >>always negative
Series resonance
for series-connected components, the condition inwhich the capacitive and inductive reactancescancel
Adding Impedance Vectors
*In reality, there is resistance, as well as reactance, inan ac series circuit containing a coil and capacitorbecause the coil wire has significa nt resistance (itsnever a perfect conductor) or because a resistor isdeliberately connected into the circuit.
Series RLC Circuits
*Resistance R can be imagined as belonging entirelyto the coil
Z = R + j (X L + X C)
Complex Admittances in Parallel
Y = (G 1+G 2) + j(B 1 + B2)
Pure Susceptances:
B = BL + BC
jBL = - j / (2fL) >>always negative jBC = j2fC >> always positive
Parallel resonance
for parallel-connected components (LC circuit), thecondition in which the capacitive and inductivesusceptances cancel
Parallel GLC Circuits
*The resistance is thought of as a conductance, whosevalue in Siemens (S) is equal to the reciprocal of thevalue in ohms. Also, the conductance is imagined tobelong to the inductor
Y = G + j (B L + BC)
Admittance to Impedance Conversion:
R = G / (G 2 + B2)X = B / (G 2 + B2)
1. Find the conductance G = 1/R for the resistor. (It will bepositive or zero.)
2. Find the susceptance B L of the inductor using theappropriate formula. (It will be negative or zero.)
3. Find the susceptance B C of the capacitor using theappropriate formula. (It will be positive or zero.)
4. Find the net susceptance B = BL + BC (It might be positive,negative, or zero).5. Compute R and X in terms of G and B using the
appropriate formulas.6. Assemble the vector R + jX.
Reducing Complicated RLC Circuits
Series CombinationR >> SeriesL >> SeriesC >> Parallel
Parallel CombinationR >> ParallelL >> Parallel
C >> Series
Impedance bridge
measures R and X at various frequencies
Ohms Law for AC Circuits
Purely Resistive Impedances
V = IZ
Complex Impedances
Series RLC: Z2 = R2 + X2 Parallel RLC: Z2 = R2X2 / (R 2 + X 2)
*Consider only the positive square root of the answer for Z
Note: In an RX ac circuit, there is always a difference in phasebetween the voltage across the resistance and the voltageacross the reactance. The voltages across the componentsalways add up to the applied voltage vectorially, but not alwaysarithmetically. It is also the same case for current computations.
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CHAPTER 17: POWER AND RESONANCE IN AC CIRCUITS
What is power(P)?
Power is the rate at which energy is expanded,radiated or dissipated. (W,Kw,Mw,mW,nW)
Watt = joule/secP = EI
where E - volts
I - ampere
Then P is in volt-ampere (VA) or VA power or Apparent Powerinstantaneous power
The constant change in power
in a pure resistance circuit true power = V power If ac circuit contains reactance (inductive, capacitive)
VA > true power and the extra power is called"imaginary power" or "reactive power"
* In a circuit with inductive reactance, the current lagsthe voltage by up to 90 degrees
* In a circuit with capacitive reactance, the currentleads the voltage by up to 90 degrees
Power factor (PF)
ratio of true power to VA, Pt/Pva or PF= cos phaseangle
* If there is no reactance Pt = Pva therefore PF=1 * If there is no resistance and purely reactance Pt=o
then PF = 0
Phase angle
the extent to w/c the curent and voltage differ inphase
* If there is no reactance phase angle = 0 * If pure reactance phase angle = 90 and -90
elsewhere
impedance mismatch
occurs when pure resistance is not equal tocharacteristic impedance, and it can be corrected bymeans of "Matching transformer".
Maxima
current/voltage is high, also called loops
Minima
current/voltage is low, also called nodes * At current loop the voltage is minimum (voltage
node) and at current node voltage is max (voltage
loop)
Transmission line mismatch loss
also known as standing wave loss, occurs in the form ofheat dissipation
resonance
condition where in the capacitive and inductivereactance cancels out.
Resonant frequency (Fo)
lowest frequency at w/c resonance occurs. also knownas fundamental frequency
Fo = 1/[2pi(LC)^1/2]
standing wave
also known as a stationary wave, is a wave thatremains in a constant position. This phenomenon can
occur because the medium is moving in the oppositedirection to the wave, or it can arise in a stationarymedium as a result of in terference between two wavestraveling in opposite directions
series resonance
There is no opposition of alternating current at resonantfrequency
Parallel resonance
There is a large opposition to alternating current @ Fo.
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CHAPTER 18 : TRANSFORMERS AND IMPEDANCE MATCHING
Transformers can:
Stepping up or down a voltage Matching impedance Provide DC isolation Balanced to Unbalanced (vice versa)
In its simplest definition, a TRANSFORMER CHANGES one voltage
to another voltage value, either higher or lower (step-up or stepdown); kaya siya tinawag na TRANSFORMER!
How does a transformer do that?
When two wires are near each other, and one of themcarries a fluctuating current, a current will be induced in theother wire. This effect is known as electromagnetic induction(Isipin niyo antenna).
- Mas malapit mas malakas ang induced current- Pero mas lalakas kung the wires are wound into coils
and placed along a common axis
- Pero di pa dyan natatapos, even more coupling , orefficiency of induced-current transfer, is obtained if thetwo coils are wound one atop the other
First Coil = Primary Winding -----------Secondary Coil = Secondary Winding
Note:
As the frequency increases, the needed inductancedecreases. At high-resistive impedances, moreinductance is generally needed than at low-resistiveimpedances.
Turns Ratio:
ratio of the number of turns in the primary to thenumber of turns in the secondary
E = voltage ; T = turns
For a transformer with excellent coupling; the relationship is:
Primary to Secondary turns ratio
Step Down : Ratio is greater than 1 : Larger number overSmaller number
Step Up : Ratio is less than 1 : Smaller number overLarger number
(Siyempre babaliktad yung mga conditions kapag Secondary toPrimary na yung ratio)
Transformer Cores:
Why use cores?
To confine the flux thus increasing the coupling or theefficiency of the induced-current transfer
Air Core Ferro-Magnetic Core
Laminated Iron
Used at 60-Hz utility ac and low audio frequency Sheets of silicon steel glued together in LAYERS Called transformer iron or plain iron Layers are used instead of a single mass of metal to
prevent eddy currents Eddy currents go in circles , heating up the core and
wasting energy; pero pag layered hindi maka-flow ngmaayos yung mga eddy currents in circles kayanapipigilan
Laminated cores exhibit high hysteresis loss above
audio frequencies Therefore not good above a few kilohertz.
Hysteresis loss
core materials become sluggish (bumabagal yungresponse) in accepting fluctuating magnetic field
Ferrite
Frequencies up to FEW megahertz and works well for RF(radio-frequency) transformers
High Permeability and concentrates flux efficiently High permeability REDUCES the number of turns
needed in the coils Higher than few megahertz; shows losses and becomes
ineffective
Permeability
is a measure of how well a material will "conduct" amagnetic field.
Powdered Iron Core
works well at VHF (very high frequency); 100 Mhzpataas.
permeability is less than that of ferrite but at highfrequencies it doesnt matter
At Radio Frequency above a few megahertz; air coresare preferred!
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Transformer Geometry:
Utility Transformer
E-core common core is the E-core so called because of its
shape winding method includes the shell and the core
winding method shell method provides the best coupling however
capacitance occurs (may or may not be tolerated)
and also cannot handle very much voltage nasa middle bar lang yung winding ng primary andsecondary
core winding method ; primary is at the bottome of theE-section and the secondary is placed at the top
capacitance is much lowe r and can handle highervoltages
both are universally employed at 60 Hz
Solenoidal Core
more commonly used as a loopstick antenna inportable radio receiver and in radio direction findingequipment
as a loopstick; primary serves as receiver andsecondary matches impedance
core windings may be on top of each other orseparated (to reduce capacitance)
Toroidal Core
donut-shaped ring of powdered iron or ferrite used for radio frequency transformer windings maybe on top or on separate parts confines the magnetic flux in the core material
(pwedeng itabi sa ibang components)provides more inductance per turn
Pot Core
even more inductance per turn can be obtained
self shielding primary and secondary must be wound on top or next
to each other (no choice) therefore capacitance is rather high generally employed at lower frequencies because you
dont need much inductance at higher frequencies
Autotransformer
when its not necessary to provide DC isolation single- tapped winding
found sometimes on radio-frequency receiver ortransmitter
works well in impedance matching Can be (but not often) used in utility circuits steppingdown by a large factor but only step up a few percent
Power Transformer
At the generating plant:
extremely high voltages are used why ? Because lower current means reduced loss in the
transmission line recall P = IE cant control the wire resistances and the power used
at the loads; the only parameter we can change is thevoltage
as a result massive transformers are used to handle thehigh voltage
Along the line:
step down transformers are used . Why? voltage from plants amount to around kilovolts , (isipin
niyo kung ang outlet niyo sa bahay naglalabas ngganung kataas na voltage baka lalapit palang kayomay tumalon ng kuryente sa inyo), that is why there is aneed to step down the voltage
At individual houses and buildings:
voltage is further stepped down to 234-V electricity inthree phases (separated by 120 degrees ) or 117-Voutlet supplies just one phase (ground yung thirdprong)
Audio-Frequency Transformer
Frequencies are higher and exist as band offrequencies (20 Hz to 20 kHz)
transformers used are still similar but instead ofchanging voltages; they MATCH IMPEDANCES
Isolation Transformer
isolating two circuits by not directly connecting them only allows AC but not DC the amount of capacitive coupling can be greatly
reduced (by separating the wires)
Balanced and Unbalanced load (Balun)
balanced = terminals can be reversed without anyeffect on the circuit (resistor , antenna)
unbalanced =must be connected in a certain way towork properly (usually when one side is connected tothe ground) ex. Coaxial lines
the transformer can allow for the mating of thebalanced and the unbalanced load
the turns ratio might be 1:1 if the impedances arematched ; if the impedances doesnt match the turnsratio should be changed
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Transformer Coupling
used in amplification by offering some advantages(usually in radio-frequency receiver and transmitter)
too many feedback, amplifiers would start to oscillatedegrading the performance BUT transformer minimizethe capacitance preventing oscillation
Impedance Transfer Ratio
To match the impedances in radio-frequency and
audio frequency circuits
For purely resistive impedances:
Z=impedance ; E = voltage ; T = turns
Radio-Frequency Transformer
Coil types
Powdered-iron cores ----->>> quite highfrequencies
Toroidal cores ----->>> most commonbecause self-shielding
Number of turns depends on the frequency , and also on thepermeability of the core
Air-core ----->>> although low permeability also haslow hysteresis loss
One disadvantage is the magnetic flux extends outside the coilMajor advantage of coil type transformer, (especially toroidalcore) is that they can be used over a wide band of frequencies such as from 3.5 MHz to 30 MHz (broadband transformers)
Transmission-Line types
transmission lines are sometimes used as impedancetransformer due to its own characteristic impedance
always made from quarter wave sectio ns or (length
of quarter wave section)
where Lft is the length of the section in feet, v is thevelocity factor expressed as a fraction, and f o is the frequency ofoperation in megahertz. If the length Lm is in meters,
-Let a quarter-wave section of line, with characteristicimpedance Zo , be terminatedin a purely resistive impedance Rout . Then the input impedance isalso a pure resistanceRin , and the following relationship holds:
These relationship will hold at frequency f o , a line 1/4wavelength long ; Neglecting losses will also hold true forodd harmonics at 3 f o , 5 f o , 7 f o , and so on.
the quarter wave matching section should be madebalanced (for loads that are balanced) and
major disadvantage is working only at certainfrequencies
Reactance
unfortunately hinde purely resistive ang mgaimpedance
Reactance makes a perfect match impossible!! Nomatter what the turns ratio or Zo of the transformer, areactance would always exist which can be toleratedat lower radio frequencies (below about 30 MHz) but a
near-perfect match becomes more important athigher frequencies although hinde sakop ng chapter na ito. Recall na
kapag may reactance (X) not equal to zero, to cancelit, add an equal and opposite (-X) which can be doneby adding an inductor or capacitor in series sa load
transmatch
is a device that i s wide band and has adjustableimpedance-matching and reactance cancellingnetworks located between the antenna and thetransmitter (from 1.8 Mhz to microwave).