Basic Electricity AND Magnetism Basic EL PDF

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PART 1 BASIC ELECTRICITY MAGNETISM

AND

BASIC ELECTRICITY I. ELECTRICITY 

A phenomenon that is associated with the presence and motion of electrons and other charged particles

1. ATOMIC STRUCTURE Substances Matter  composed of atoms which are made up of nucleus around which an infinitesimal charge revolves Atom  a substance consisting of electrons, protons and neutrons Element  substances consisting of atoms of only one kind Compound  Combination of 2 or more different atoms or elements. Molecule  smallest part of a compound that retains the properties of the compound Particles of an Atom Electron  basic quantity for a negative charge  can be valence electron being the electrons of the outermost shell  can be bound electrons being the electrons of the inner bands  can be free or conduction electrons being electrons that are free to move Proton  basic quantity for positive charge Neutron  neutral particle in atom

Particle

Charge,Coulomb

Mass, kilogram

electron proton

-1.602x10-19 +1.602x10-19

9.109x10-31 1.673x10-27

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neutron

1.673x10-27

none Table1. Elementary Particles

Bohr Model  planetary-like structure of representing an atom

N= 2n 2

N = no. of electrons in each orbit n = Orbital number 1 for K-shell, 2 for L-shell, 3 for M-shell and so on. 2. ELECTRICAL CLASSIFICATIONS of Material Conductors  materials with less than 4 valence electrons  allows electrical current to flow easily  Example: Cu, Al, Au, Ag… Insulators  Materials with more than 4 valence electrons  prevents the flow of electrical current  Plastics, glass, ceramics, rubbers etc Semiconductor  with exactly 4 valence electrons  have electrical characteristics in between conductor and insulator 3. ENERGY BANDS Energy Gap  energy difference between the valence and conduction band  1.1eV for Si ; 0.67eV for Ge Valence Band  region of the valence shell and valence electrons Conduction Band ElЄcҐrøniX

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 region where free electrons are said to be present Forbidden Band  region where no electron exist

II. BASIC ELECTRICAL QUANTITIES 1. CHARGE (Q or q)    

static electricity at rest, without any motion the result of work done in separating electrons to its atoms coulomb(C), unit for electrical charge named after Charles Coulomb 1 coulomb = 6.25x 1018 electrons (e-)

Laws of Electric Charges a. Unlike or dissimilar charges attract each other b. Like or similar charges repel each other Coulomb’s Law “The force between charges is proportional to the amount of charges and inversely proportional to the square of the distance between charges”

F=

kQ1 Q 2 r2 Where: Q1 and Q2 = point charges k = 8.98 x 109 Nm2/C2 (SI) r = distance or separation

2. CURRENT (I or i)      

rate of charge in motion a continuous flow of free electrons I = Q / t : 1 ampere = 1 coulomb/second Ampere(A) is the base unit of current, named in honor to the French physicist Andre Marie Ampere DC current flows only in 1 direction AC current flows in alternate direction periodically

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3. ELECTROMOTIVE FORCE(emf or e)  force that is used to move the charged particles such as electrons Electric Potential  the ability of a charged body to do work on charged particles such as electrons Voltage (V)  A potential energy difference (or simply, P.D.) that exists across two points which tend to cause a flow of electrons.  Volt (V) is the unit of potential difference and named after Italian physicist Alessandro Volta. 1 volt will push 1 ampere of current through 1 ohm resistance  V=W/Q i.e., Volt = 1 Joule / Coulomb or 1 Newton – meter / Coulomb 4. RESISTANCE (R or r)  a property of electric circuit, material, and substance that: 1. tends to limit the amount of current that can be produced by the applied voltage 2. converts electrical energy into heat energy  Ohm(Ω), the basic unit of resistance named after George Simon Ohm  1Ω= 1V/1A Resistance Law “The resistance of a conducting material is directly proportional to its length (R  L) and inversely proportional to its cross – sectional area (R  I/A).” R=

L A

Where: R = wire resistance in Ω ρ = resistivity in Ω-cm (10-6 Ω-cm for copper) L =length of the wire A =cross-sectional area

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Resistance with Temperature R 2 = R1 [1 + 1 (T2 – T1)] R 2=

R1 (| T0 | T2 ) (| T0 | T1 )

 2 = 1 [1 + 1 (T2 – T1)] Where: R2 = resistance at temperature T1 R1 = resistance at temperature T2 1 = temperature coefficient of resistance=1/ ( IToI+T1) To = inferred absolute zero temperature coefficient = - 234.5C Annealed copper = - 242C Hard drawn copper = - 236C Aluminum

Temperature Coefficients 1. Positive Temperature Coefficient  Resistance increases as temperature increases  Pure metals 2. Negative Temperature Coefficient  Resistance decreases as its temperature increases  Semiconductors and Metal oxides 3. Zero Temperature Coefficient  Resistance remains constant even there is change in temperature.  Alloys 5. CONDUCTANCE (G)  Conductivity () is the reciprocal of resistivity.  Siemen (S), unit of conductance formerly known as mho 6. Impedance, Admittance, Reactance and Susceptance Impedance (Z)  Combination of resistance and reactance in AC circuit Admittance (Y)  Reciprocal of impedance Reactance (X) Macro Integrated Training and Review Center

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 Opposition to current offered by capacitive and inductive elements Susceptance (B)  Reciprocal of reactance 7. Work, Power and Energy Work (W)  The accomplishment of motion against the action of a force which tends to oppose the motion.  Joule, SI unit of work or energy  1 Joule = 1 Newton-meter = 1 Coulomb / Volt  Electronvolt (eV), unit of energy for single electron  1eV=1.6x10-19 J Power (P)  rate of producing work or consuming energy

   

P = W / t = VI = I2R = V2 / R Watts – the S.I. unit of electric power named after James Watt Horsepower (Hp) – power rating of electric motor 1 Hp = 746 Watts or 0.746 KW

Energy  Ability to do work  For heat energy: 1 Kcal=4180 J , 1BTU=778.16 ft-lb

Q = mC∆T

where: Q = heat M = mass C = specific heat ∆T= change in temperature

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III. BASIC ELECTRICAL / ELECTRONIC COMPONENTS 1. RESISTOR  device having known specific values of resistance in ohms(Ω) that limits the amount of current flowing through it  can divide the voltage in a circuit  with power rating that show how much power can be safely dissipated a. Types: Fixed Resistors:

1. Nichrome Wire  offers few ohms of resistance  resistance wire 2. Carbon Composition  1/8 W to 2W in rating, and its ohmic rating can be determined by its color code. 3. Wire - Wound  they are very accurate and its ohmic and wattage (above 2W) is painted on its covering. Can be made from a nichrome wire wound around a ceramic core.  Wattage ranges from 5W to 100 W 4. Metal Film  use a thin film of metal or a metal particle mixture to achieve various resistances. Variable Resistors

1. Rheostat  two terminal variable resistor  in series with the load to vary current 2. Potentiometer (“pot”)  three terminal variable resistor  Connected in a circuit to vary the voltage.  Taper of a potentiometer refers to the way in which the resistance changes in relation to the position of its slider 3. Trimmer/ Trimpots  a potentiometer equipped with a plastic thumbwheel, or a slot for a screwdriver, for occasional adjustment. Non-Linear or Non-Ohmic Resistors

1. Thermistors  Temperature sensitive resistors. Macro Integrated Training and Review Center

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 Uses: protective device, temperature measurement or control. 2. Varistors, or Voltage Dependent Resistors (VDR)  Voltage sensitive resistors. 3. Photoresistors, or Light Dependent Resistors (LDR)  Light sensitive resistors.  Use: sensing light, sense people or items passing a point, adjust television picture brightness to match room light. b. Carbon Resistor Color Coding First significant digit Second Significant Digit

Tolerance

Multiplier

COLOR

BAND1

BAND2

Multiplier

Tolerance

Black Brown Red Orange Yellow Green Blue Violet Gray White Gold Silver No Color

0 1 2 3 4 5 6 7 8 9 ----

0 1 2 3 4 5 6 7 8 9 ----

100 101 102 103 104 105 106 107 108 109 0.1 0.01

-1% 2% 3% 4% -----5% 10% 20%

Table 2: Resistor Color Code

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2. INDUCTOR  opposes change in current  allows DC but blocks AC  stores energy by concentrating the magnetic field of current  also known as choke  termed as solenoid for coil with more than one turn a. Inductance (L)  property of a circuit that opposes the change in current expressed in Henries(H)  for a N-turn coil wound around a certain core, it is defined as the amount of flux linkage of the coil per unit current through the coil  1H=1Weber/A

L=

 0 r AN2

Where: μr = relative permeability

L µ0 = material permeability A = area N = no. of turns L = length

b. Time Constant (λ)  One time constant is the amount of time for an inductor to energize and deenergize up to 63.2 % L where: L- inductance λ= R R- resistance

c. Instantaneous Current of an inductor  The amount of current flowing through the inductor at certain time instant E - (t/λ)

I (t) =

R

(1+e

)

d. Voltage across an inductor di

V inductor = L(

)

dt d  ) V induced = N( dt

: di/dt = rate of change in current where: N = number of turns dø/dt = rate of change in flux

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e. Energy stored in an inductor W= ½LI2 where: W- stored energy I – current

f. Inductive Reactance

XL = 2πfL

where: XL = inductive reactance f = frequency

g. Total Inductance

L series = L1 + L2 +… +Ln L parallel = (

1 -1 1 1 + + …+ ) Ln L1 L2

With mutual inductance:

L aiding = L1 + L2 + 2M L opposing = L1 + L2 - 2M M=k

L1L2 Where: M = mutual inductance

k = coefficient of coupling

h. Types of inductor: Air-core Inductor  Used for radio frequency applications  Inductance in μH to mH  Typical coefficient of coupling from 0.05 to 0.3 Iron-Core Conductor  Used for 60-Hz and audio frequency applications  Inductance from 1H to 25H  Typical coefficient of coupling equals 1

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3. CAPACITOR  Stores electric energy  Previously called as condenser (deprecated)  Essentially consists of two conducting plates called electrodes separated by a layer called dielectric. a. Capacitance(C)  The electrical size of the capacitor  A measure of how much electric energy a capacitor can store expressed in Farads (F)  Previously called capacity (deprecated) and permittance (obsolete)  Permittivity(ε) is a measure of how well a dielectric will permit the establishment of flux lines within the dielectric

C=

Q E

where: C = capacitance in farad, F Q = charge stored in Coulomb, C E = voltage across the capacitor in volt, V

C=

 or A d

where: εo = absolute permittivity = 8.854 x 10-12 F/m εr = dielectric constant A = area of parallel plates, m2 d = plate separation, m

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Dielectric

Dielectric Constant

Air or Vacuum Polyvinyl Aluminum Oxide Glass Tantalum Paper Mica Ceramic

1 3.3 7 8 25 2 to 6 3 to 8 80 to 1200

Table 3: Dielectric constants of material

For multi-plate construction of capacitor:

C = (n-1)

o  r A where: n = no. of plates d

b. Elastance (S)  The reciprocal of capacitance  Has a unit of daraf S=

1 C

c. Uses of Capacitor  Blocks DC  Couples AC  Filter  Tuning  Signal Generation  Energy Storage d. Time Constant (λ)  One time constant is the amount of time for an inductor to energize and deenergize up to 63.2 % λ= RC

where: C = capacitance R = resistance

e. Charging and Discharging Equations V charging = E (1 - e-t/RC) where: E = source voltage V discharging = E (e-t/RC) ElЄcҐrøniX

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f. Current through Capacitor

Ic = C (

dv ) dt

where: Ic = current in a capacitor dv/dt = rate of change in voltage

g. Energy Stored in a Capacitor

W= ½CV2

where: W = stored energy V = voltage

h. Capacitive Reactance

Xc =

1 2fC

where: Xc = inductive reactance f = frequency

i. Total Capacitance

C series= (

1 -1 1 1 + + …+ ) Cn C1 C2

C parallel = C1 + C2 +… +Cn

j. Types of capacitor: Fixed Capacitors

a. Mica  Capacitance values range approximately 1pF to 0.1μF  Used over a wide temperature range (-55 to +150°C) b. Paper  Packaged as a “rolled sandwich”  Variety of values, 500pF to 50µF  Operating ambient temperatures is as high as 125°C c. Plastic Film  Plastics used include polystyrene, polycarbonate, and polyester (Mylar)  Available in typical ranges 500pF to 10μF d. Ceramic  Low-k ceramic capacitor is widely used in temperature compensation network  High-k ceramic capacitor change their value appreciably with temperature, dc voltage and frequency

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e. Electrolytic  Can be aluminum and tantalum and either polarized or non-polarized  Used where large value of capacitance in a small volume is required. Variable Capacitors

a. Air variable  Capacitance values ranges from a few picofarads up to 500pF  Maximum voltage rating is 9kV b. Trimmer  Utilized for fine tuning and in hybrid microelectronics circuit Chip Capacitors

 

No larger than a match head Volumetric efficient

k. Capacitor Failures Catastropic



A short circuit caused by dielectric breakdown or an open circuit caused by connection failure

Degradation



Results in a gradual decrease in leakage resistance and hence gradual increase in leakage current

l. Other Parameters Voltage Rating



Specifies the maximum DC voltage that can be applied without the risk of damage

Temperature Coefficient



Indicates the amount and direction of a change in capacitance value with temperature

Leakage Current



The current that result in the total discharge of a capacitor if the capacitor is disconnected from the charging network

Working Voltage



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The voltage that can be applied across a capacitor for long period of time

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MAGNETISM I. MAGNETISM 

A natural phenomenon in which some material (ferromagnetic) can be attached by a magnet but not other material (non-magnetic).

1. ATOMIC THEORY of Magnetism    

Magnetism is the effect of moving charged particles such as the motion of electrons in an atom In atoms in most elements, the magnetic forces produced by its charged particles, electrons and protons cancel its other. They are called nonmagnetic material. The common elements whose magnetic forces do not cancel completely are called magnetic material. Domains are completely magnetized.

2. MAGNET          

A substance that attracts pieces of iron (and its compound), steel, nickel, cobalt. Natural magnet exhibits permanent magnetism Lodestone, a natural magnet Artificial magnets produce by exposing or subjecting a magnetic material into a magnetizing force Alnico, permanent magnet often used in speakers Hipernik is used in high power transformers Keeper, placed across poles to maintain strength during storage Air gap, air space between poles of magnet Degaussing, another name of demagnetization Curie temperature, temperature where materials lose magnetism 600° C - ferrite 280° C – broadline 100° C – YIG (Yttrium-Iron-Garnet)

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II. MAGNETIC QUANTITIES Magnetic Field

flux

1. FLUX (ø)  Known as the magnetic lines of force  Represent the lines which seem to emanate from north and terminates to South Pole.  Maxwell (Mx), cgs unit of flux named after Scottish physicist, James Clerk Maxwell(1831-1879)  Weber (Wb), SI unit of flux and named after German physicist Wilhelm Weber(1804-1891) Characteristic of Magnetic Lines of Force: - They possess a positive direction - They always form a complete loop - They tend to become as short as possible - They repel one another - Like poles repel one another - They arrange to set up their maximum number

2. FLUX DENSITY (β)  Specifies the amount of magnetic lines per unit area(A)  Gauss (G), cgs unit and name after Johann Karl Freidrich Gauss(17771855)  Tesla(T), SI unit and named after Croatian engineer Nikola Tesla(18561943)

β=ø/A

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3. MAGNEMOTIVE FORCE (mmf)  Amount of magnetizing force or magnetic potential  Coercive force, needed to reduce flux density to zero  Domain, arrangement of atoms under mmf  Gilbert(Gb), cgs unit and named after William Gilbert(1540-1603)  Ampere-turn, Si unit

mmf = IN

where: I = current , N = no. of turns

4. MAGNETIC FIELD INTENSITY (H)  Amount of magnemotive force per unit length  Oersted (Oe), cgs unit and named after Danish physicist Hans Christian Oersted(1777-1851)  Ampere-turn per meter, SI unit

H=

mmf length

Magnetic Units Conversion Quantity Flux (ø) Flux Density (β) Magnetomotive force (mmf) Field Strength (H)
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