INTRODUCTION
Electronics
is branch of engineering that deals with the control of electricity in a
vacuum, such as vacuum tubes, in gas or vapour or in solid semiconductors
materials used for transistor and integrated circuits.
In
electronics there are two types of sources are used.
1. AC Sources
2. DC Sources
AC SOURCES -
Alternating
current or voltage reverses between Positive and Negative Polarities and varies
in amplitude and time.
1. Alternators
-
An
alternator is machine which is used for producing alternating current.
2. Oscillators
and signal generators -
An
oscillator is a device which converts direct power into alternating power.
An oscillator is main part signal generator. A signal generator produces ac signals at its output. The voltage and frequency of ac signals can be varied.
DC SOURCES -
The Reason
for unidirectional current is that a dc source maintains the same polarity of
output voltage.
1. Batteries -
A battery is group of cell that generates electric energy
from their internal chemical reaction.
The cell consists of two different conducting materials called
the electrodes, immersed in electrolyte.
The cell used in torch is of primary type. Primary cells
can’t be recharged. Nickel-cadmium cells and Lead Sulphuric acid wet cell are
of secondary type. These cells can be recharged many times.
2. DC generators -
A dc generator is similar to an alternator.
When its shaft is rotated at specified speed by an external
agency such as steam turbine or water turbine, a voltage of rated value can be
produced.
3. Rectifiers -
A rectifier converts an alternating current into a direct
current.
POWER -
The rate of doing work is called power.
Unit of power is joule/second or watt. Power in watts=V*I.
IMPORTANT FORMULAE -
1. If resistors are in series, total resistance Rs is given
by,
Rs=R1+R2+R3+…
2. If resistors are in parallel, total resistance Rp is given
by,
Rp=1/R1+1/R2+1/R3+…
KIRCHOFF’S CURRENT LAW
(KCL) - The total
current flowing towards a node in circuit is equal to the total current away from
that node.
KIRCHOFF’S VOLTAGE LAW (KVL) - The algebraic sum of the voltages around any closed
loop is zero.
ELECTROMAGNETISM
The magnetic field is invisible. The magnetic field is the
strongest at the poles. The field decreases in strength inversely as the square
of the distance from the poles of the magnet.
1. Magnetic Flux (Φ) -
The entire group of magnetic field lines, which can be
considered to flow outward from the north pole of magnet, is called magnetic
flux. Its symbol is (ϕ).
2. Flux Density (B) -
The number of magnetic field lines per unit area of a section
perpendicular to the direction of flux is called flux density.
B= ϕ/A.
where ϕ is the flux through an area A.
S.I unit of flux density is Tesla (T)
3. Induction By The Magnetic Field -
The electrical effect of one body on
another without any physical contact between them is called induction. Thus a permanent
magnet can induce an unmagnetized iron bar to become a magnet, without touching.
4. Magnetic Potential -
In an electric circuit, the current is due to the existence
of an electromotive force. In a Magnetic circuit the magnetic flux is due to
the existence force. In a magnetic circuit the magnetic flux is due to the
existence of a magnetomotive force (mmf) caused by the currents flowing through
the turns of a coil. The magnetoomotive force is also known as magnetic
potential or magnetizing force.
Magnetic Potential = NI
Where N= Nmber of turns and I = current in amperes.
S.I unit – Ampere (A)
5. Field Intensity -
The magnetic potential or mmf per meter length of
the magnetic circuit I called field intensity or magnetic length.
H = NI/l
S.I Unit – A/m
6. Permeability (µ) -
The ability to concentrate magnetic flux is called
permeability. Any material the is easily magnetized has high permeability.
7. Reluctance -
Opposition to production of flux in a material is
called its reluctance. Reluctance is inversely proportional to permeability.
Reluctance = mmf/ϕ
Unit – Ampere.turns/Weber
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