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UNIT 5 : CAPACITORS AND CAPACITANCE (CAPACITOR EQUIVALENTS CIRCUIT…
UNIT 5 :
CAPACITORS AND CAPACITANCE
CAPACITOR AND CAPACITANCE
TYPES OF CAPACITORS
FIXED
UNPOLARISED
MICA
CERAMIC
FILM
AIR - GAP
PAPER
POLARIZED
ALUMINIUM
TANTALUM
VARIABLE
TRIMMER
CAPACITOR CONSTRUCTION
The simplest construction of a capacitor is by using two parallel conducting metal plates separated through a distance by an insulating material, called a the dielectric as summarised below. A capacitor consists of two metal plates separated by a dielectric
The dielectric material allows for charge to accumulate between the capacitor plates.
Air ;actually vacuumͿ has the lowest dielectric value of ɸo = 8.854 x 10^(-12) Farads/meter. All other
materials have higher dielectric values, since they are higher in density and can therefore
accumulate more charge.
ASSOCIATED QUANTITIES
1) Microfarad (μF) : 1μF = 1/1,000,000F = 10^(-6)F
2) Nanofarad (nF) : 1nF = 1/1,000,000,000F = 10^(-9)F
3) Microfarad (pF) : 1pF = 1/1,000,000,000,000 = 10^(-12)F
used to store electrical energy.
The unit of capacitance is Farad. The symbol of capacitance is C.
Capacitance is defined to be the amount of charge Q stored in between the two
plates for a potential difference or voltage V existing across the plates.
CAPACITOR EQUIVALENTS CIRCUIT
CAPACITOR CONNECTED IN PARALLEL
CAPACITOR CONNECTED IN SERIES - PARALLEL
CIRCUIT CONNECTED IN SERIES
CIRCUIT WITH CAPACITIVE LOAD
ELEMENTS RELATED TO CAPACITANCE
ELECTRIC FIELD
Area that surrounds the electric charge or charges system where the
increasing and decreasing of electric force exists.
LINE OF ELECTRIC FORCE
A line of electric force is known as line or curve that pointed out from
positive charge (+) to negative charge (-) in a magnetic field.
ELECTRIC FLUX
Known as amount of electric force line pointed out from positive charge (+)
to negative charge (-) in a magnetic field. Flux symbol is Ψ(phi).
ELECTRIC FLUX DENSITY (D)
Electric flux density is a measurement of electric flux that pass through a
unit of plate͛s area with a coincide angle͕ that is an area of 1 meter^2
The ratio between the charge of the capacitor and capacitor plates.The symbol used is D.
D = Q/A
Q= charge(Coulomb),A = surface area of capacitor
ELECTRIC FIELD STRENGTH
When two metal plates are charged and separated in a certain distance, a
potential difference will exists between the plates.
A force was also generated, known as electric force and the symbol is E. The magnetic strength depends on the potential difference and distance between plates.
E = V / d
V= potential difference, d= thickness of dielectric
DIELECTRIC
Insulator that is used between the two plates of a capacitance is known as
dielectric.
Electric field exists in the dielectric and the flux density depends on the types
of insulator used.
ABSOLUTE PERMITTIVITY (ɸ)
Permittivity is a capacitance or ability to store energy of a capacitor.A force was also generated, known as electric force and the symbol. It depends on the dielectric substance, and the symbol is ɸ.
ɸ = D / E
FACTOR THAT EFFECTING CAPACITANCE
a. Capacitance between two plates proportional to the surface area
b. Capacitance between two plates inversely proportional to the thickness of dielectric
c. Increasing the dielectric constant of the material between the plates
PROCESS CHARGING AND DISCHARGING IN CAPACITOR
CHARGING PROCESS IN CAPACITOR
In initial state, a capacitor is uncharged( Vc = 0V). When a capacitor start
charged, maximum current will be flowing (i = I(max).. The current would be decreased by
exponent, while voltage will be rising by exponent also. This state will continue until fullstate (steady) achieved. In this full state, current had decreased to zero value, while voltage increased until maximum value. The capacitor is s said in fully charge.
Time constant,τ= CR
The times taken for voltage achieve value of 0.632Vmax and current achieve value of
0.371 I(max)
Initial current,I(max) = V/R
DISCHARGING PROCESS IN CAPACITOR
When capacitor fully charge and then switch being transformed to ͚b͕͛ discharge process for capacitor will happen. The time taken to recharge and fully discharge is 5τ=CxR.
ENERGY STORED IN A CAPACITOR
During charging process through capacitor, it will get energy. Energy is kept in
static form.The voltage in capacitor will increase from 0 volt to E volt.
W = 1 / 2 ( C(E^2)) Joule
UNIT 6:
INDUCTOR AND INDUCTANCE
Inductor and inductance
Construction of inductor
An inductor is usually constructed as a coil of conducting material, typically
copper wire, wrapped around a core either of air or ferrous material.
Core materials with higher permeability than air confine the magnetic field
closely to the inductor, thereby increasing the inductance.
constructed as enamel coated wire wrapped around a ferrite with wire
exposed on the outside, while some enclose the wire completely in ferrite and are called
͚shielded͛͘
Associated quantities
1) Inductor, also called a choke, is another passive type electrical component designed to take advantage of this relationship by producing a much stronger magnetic field than one that would be produced by a simple coil.
2) Symbol of inductance is L.
3)Unit of inductance is Henry. 4)Inductance ʹ the property of an electric circuit by which an electromotive force is
induced in it as the result of changing magnetic flux. 5)Electromagnet ʹ temporary magnet production due to flow of electric current.
6)Electromagnetic induction - production process electric form magnet.
Types of inductor
Inductance equivalents circuit for series and parallel connection
Inductors connected in series
Inductors connected in parallel
Inductors connected in series-parallel
Rise and decay of current goes through an inductor in the dc circuit
Time constant
Time constant at rise of current
Time constant at decay of current
Energy stored in an inductor
An inductor possesses an ability to store energy.
E = (1/2)(L(I^2))
Rise and decay of current
1) When switch in 'a' position͕ inductor connected to DC supply.The current had not achieved maximum value immediately.The current are going to reach maximum value in a period of time that certain caused by production e.m.f induced by inductor which always against the supply voltage. So, current of the circuit is
rise delayed.
2) When switch is being transformed to position ͚'b' inductor circuit had short
circuit (no supply voltage).The current is not decrease continue to zero but take a time
that certain from maximum value until zero value.
Circuit with inductive load
Electromagnetic induction
When a conductor is moved across a magnetic field so as to cut through the lines of
force (or flux, an electromotive force (e.m.f) is produced in the conductor.
If the conductor forms part of a closed circuit then the e.m.f produced causes an electric current to flow round the circuit.
Hence an e.m.f is induced in the conductor as a result of its movement across the
magnetic field͘ This effect is known as electromagnetic induction͛͘
Faraday's Law
An induced e.m.f is setup whenever the magnetic field linking that circuit
changes
The magnitude of the induced e.m.f in any circuit is proportional to the rate of
change of the magnetic flux linking the circuit.
The factors that influence inductance
The cross-sectional area of the coil of wire (A) ʹ the greater the cross-sectional area
the higher the inductance
The presence of magnetic core - when the coil is wound on an iron core, the same
current sets up a more concentrated magnetic field and the inductance is increased
The number of turns of wire (N) ʹ more turns the higher the inductance
The way turns are arranged ʹ a short tick coil of wire has a higher inductance than
the along thin one.
The mathematical of self-inductance
Self-inductance and the induced e.m.f
Inductance is the name given to the property of a circuit whereby there is an e.m.f
induced into the circuit by change of flux linkages produced by a current change.
When the e.m.f is induced in the same circuit as that in which the current is changing,
the property is called self-inductance, L.
Mathematical relationship between the induced e.m.f and the network
Faraday noted that the e.m.f induced in a loop is proportional to the rate of change of
magnetic flux through it:
