Diploma i boee u 1 electrostatic and capacitance

ELECTROSTATIC AND CAPACITANCE
& CURRENT ELECTRICITY
Course: Diploma
Subject: Basics of Electrical Engineering
Unit: I

What is Static Electricity?
• Static electricity is an imbalance of electric
charges within or on the surface of a material. The
charge remains until it is able to move away by
means of an electric current or electrical discharge.
Static electricity is named in contrast with current
electricity, which flows through wires or other
conductors and transmits energy.
• A static electric charge is created whenever two
surfaces contact and separate, and at least one of the
surfaces has a high resistance to electrical current
(and is therefore an electrical insulator).

What is electric charge?
• Electric charge is the physical property of matter that
causes it to experience a force when placed in an
electromagnetic field. There are two types of electric
charges positive(Protons) and negative(Electrons).
Positively charged substances are repelled from other
positively charged substances, but attracted to negatively
charged substances; negatively charged substances are
repelled from negative and attracted to positive. An object
will be negatively charged if it has an excess of electrons,
and will otherwise be positively charged or uncharged.
The SI derived unit of electric charge is the coulomb (C),
although in electrical engineering it is also common to use
the ampere-hour (Ah), and in chemistry it is common to use
the elementary charge (e) as a unit.

What is permittivity?
• Permittivity is a measure of how an electric
field affects, and is affected by, a dielectric medium.
The permittivity of a medium describes how much
electric field (more correctly, flux) is 'generated' per
unit charge in that medium.Permittivity is denoted by
‘ε’.
• Permittivity may be of 2 types:-
1) permittivity in Vacuum and 2)Absolute permittivity
1) Permittivity in Vaccum is the measure of the
resistance that is encountered when forming an
electric field in a free space or vacuum .It is denoted
ε0
2) Absolute permittivity is the measure of the
resistance that is encountered when forming an
electric field in a medium . It is denoted by ε

What is Relative permittivity?
• The relative permittivity of a material is its
dielectric permittivity expressed as a ratio of
absolute to the permittivity of vacuum. It is
denoted by ‘Εr. ‘Or ‘K’. The equation for Relative
permittivity is as below:
Εr = ε/ε0 = K
• Likewise, relative permittivity is the ratio of
the capacitance of a capacitor using that material
as a dielectric, compared to a similar capacitor that
has vacuum as its dielectric. Relative permittivity is
also commonly known as dielectric constant, a
term deprecated in physics and engineering.

Coulomb’s law for electric charge
• The magnitude of the electrostatic force of
interaction between two point charges is directly
proportional to the scalar multiplication of the
magnitudes of charges and inversely proportional to the
square of the distance between them.The force is along
the straight line joining them. If the two charges have the
same sign, the electrostatic force between them is
repulsive; if they have different sign, the force between
them is attractive.Mathematically it can be represented
by followindg formula,

What is Electric field?
• Electric field is defined as the electric force per
unit charge. The direction of the field is taken
to be the direction of the force it would exert
on a positive test charge. The electric field is
radially outward from a positive charge and
radially in toward a negative point charge…The
equation for electrisc field is given by following
formula:-
E = F/q and the unit of electric field is N/C.
Electric field from a point charge : E = k Q / r2

Cont…
In above figure electric field lines are shown.
What is electric field lines?
A more useful means of visually representing the
vector nature of an electric field is through the use of
electric field lines of force. Rather than draw
countless vector arrows in the space surrounding a
source charge, it is perhaps more useful to draw a
pattern of several lines that extend
between infinity and the source charge. These pattern
of lines, sometimes referred to as electric field lines,
point in the direction that a positive test charge would
accelerate if placed upon the line.

Cont..
• As such, the lines are directed away from positively
charged source charges and toward negatively
charged source charges. To communicate
information about the direction of the field, each line
must include an arrowhead that points in the
appropriate direction.

Cont…
• An electric field line pattern could include an
infinite number of lines. Because drawing such large
quantities of lines tends to decrease the readability
of the patterns, the number of lines is usually
limited. The presence of a few lines around a charge
is typically sufficient to convey the nature of the
electric field in the space surrounding the lines

What is electric field intensity?
• Electric field strength is a vector quantity; it has
both magnitude and direction. The magnitude of
the electric field strength is defined in terms of
how it is measured. Let's suppose that an electric
charge can be denoted by the symbol Q.
• This electric charge creates an electric field;
since Q is the source of the electric field, we will
refer to it as the source charge. The strength of
the source charge's electric field could be
measured by any other charge placed
somewhere in its surroundings.

Cont..
• The charge that is used to measure the electric
field strength is referred to as a test charge since
it is used to test the field strength. The test
charge has a quantity of charge denoted by the
symbol q. When placed within the electric field,
the test charge will experience an electric force -
either attractive or repulsive. As is usually the
case, this force will be denoted by the symbol F.
The magnitude of the electric field is simply
defined as the force per charge on the test
charge.

Cont..
• If the electric field strength is denoted by the
symbol E, then the equation can be rewritten
in symbolic form as
• .The standard metric units on electric field
strength arise from its definition. Since electric
field is defined as a force per charge, its units
would be force units divided by charge units.
In this case, the standard metric units are
Newton/Coulomb or N/C.

ELECTRIC FLUX
• Think of air blowing in through a window. How
much air comes through the window depends
upon the speed of the air, the direction of the
air, and the area of the window. We might call
this air that comes through the window the
"air flux".
• We will define the electric flux for an electric
field that is perpendicular to an area as
• ɸ = E.A

Cont..
• Think about the "air flux" of air passing through a
window at an angle . The "effective area" is A cos or the
component of the velocity perpendicular to the window is
v cos . With this in mind, we will make a general definition
of the electric flux as
ɸ = E A cosθ
You can also think of the electric flux as the number of
electric field lines that cross the surface. Remembering
the "dot product" or the "scalar product", we can also
write this as
ɸ = E . A
• where E is the electric field and A is a vector equal to area

Cont..
• where n is a unit vector pointing perpendicular to
the area. In that case, we could also write the
electric flux across an area as
ɸ = E . n A
• Both forms say the same thing. For this to make
any sense, we must be talking about an area
where the direction of A or n is constant.
• For a curved surface, that will not be the case. For
that case, we can apply this definition of the
electric flux over a small area & δA or A or δAn.

Cont..
• Electrical flux has SI units of volt metres (V m),
or, equivalently, newton metres squared
per coulomb (N m2 C−1). Thus, the SI base
units of electric flux arekg·m3·s−3·A−1.
• Its dimensional formula is [L3MT–3I–1].

CAPACITOR
• A capacitor (originally known as a condenser) is
a passive two-terminal electrical component used to
storeenergy electrostatically in an electric field. The
forms of practical capacitors vary widely, but all
contain at least two electrical conductors (plates)
separated by a dielectric (i.e., insulator). The
conductors can be thin films of metal, aluminum foil
or disks, etc. The 'nonconducting' dielectric acts to
increase the capacitor's charge capacity. A dielectric
can be glass, ceramic, plastic film, air, paper, mica, etc.
Capacitors are widely used as parts of electrical
circuits in many common electrical devices. Unlike
a resistor, a capacitor does not dissipate energy.
Instead, a capacitor stores energy in the form of
an electrostatic field between its plates.

Capacitance
• Capacitor plates • A capacitor consists of
two conductors separated by
a non-conductive region.The
non-conductive region is
called the dielectric. In simpler
terms, the dielectric is just an
electrical insulator. Examples
of dielectric media are glass,
air, paper, vacuum, and even
a semiconductor depletion
region chemically identical to
the conductors.Fig 3

Cont
• The conductors thus hold equal and opposite charges on
their facing surfaces, and the dielectric develops an electric
field. In SI units, a capacitance of one farad means that
one coulomb of charge on each conductor causes a voltage
of one volt across the device.
• An ideal capacitor is wholly characterized by a
constant capacitance C, defined as the ratio of charge
±Q on each conductor to the voltage V between them:

Cont..
• Because the conductors (or plates) are close together, the
opposite charges on the conductors attract one another
due to their electric fields, allowing the capacitor to store
more charge for a given voltage than if the conductors were
separated, giving the capacitor a large capacitance.
• Sometimes charge build-up affects the capacitor
mechanically, causing its capacitance to vary. In this case,
capacitance is defined in terms of incremental changes:

DC charging circuit for capacitor.(just
for information)
• A simple resistor-capacitor
circuit demonstrates charging of
a capacitor.
• A series circuit containing only
a resistor, a capacitor, a switch
and a constant DC source of
voltage V0 is known as a
charging circuit. If the capacitor
is initially uncharged while the
switch is open, and the switch is
closed at t0, it follows from
Kirchhoff‘s voltage law that
Fig 4

Cont..
we can get following equation by kirchoff’s law
• Taking the derivative and multiplying by C, gives a first-
order differential equation
• At t = 0, the voltage across the capacitor is zero and the
voltage across the resistor is V0. The initial current is
then I(0) =V0/R. With this assumption, solving the
differential equation yields

Cont…
• where τ0 = RC is the time constant of the system.
As the capacitor reaches equilibrium with the
source voltage, the voltages across the resistor
and the current through the entire circuit decay
exponentially. The case of discharging a charged
capacitor likewise demonstrates exponential
decay, but with the initial capacitor voltage
replacing V0 and the final voltage being zero.

Cont…
• taking the derivative and multiplying by C, gives
a first-order differential equation:
At t = 0, the voltage across the capacitor is zero
and the voltage across the resistor is V0. The initial
current is then I(0) =V0/R. With this assumption,
solving the differential equation yields
• where τ0 = RC is the time constantof the system.
As the capacitor reaches equilibrium with the source
voltage, the voltages across the resistor and the
current through the entire circuit decay exponentially.
The case of discharging a charged capacitor likewise
demonstrates exponential decay, but with the initial
capacitor voltage replacing V0 and the final voltage
being zero.

Series and parellel connection of capacitor
• Capacitors are one of the standard components
in electronic circuits. Moreover, complicated
combinations of capacitors often occur in
practical circuits. It is, therefore, useful to have a
set of rules for finding the equivalent capacitance
of some general arrangement of capacitors. It
turns out that we can always find the equivalent
capacitance by repeated application
of two simple rules. These rules related to
capacitors connected in series and in parallel.

Parellel connection
• Consider two capacitors connected
in parallel: i.e., with the positively charged plates
connected to a common ``input'' wire, and the
negatively charged plates attached to a common
``output'' wire--see Fig. 15. What is the
equivalent capacitance between the input and
output wires? In this case, the potential
difference across the two capacitors is the same,
and is equal to the potential difference between
the input and output wires. The total charge

Cont..
• however, stored in the two capacitors is
divided between the capacitors, since it must
distribute itself such that the voltage across
the two is the same. Since the capacitors may
have different capacitances, and the
charges and may also be different. The
equivalent capacitance of the pair of
capacitors is simply the ratio .
Where is total charge. It follows that

Cont..
• Here, we have made use of the fact that the
voltage is common to all three capacitors. Thus, the
rule is:
• The equivalent capacitance of two capacitors
connected in parallel is the sum of the individual
capacitances.
• For capacitors connected in parallel, above
Eq. generalizes to

Series connection
• Consider two capacitors connected in series: i.e.,
in a line such that the positive plate of one is
attached to the negative plate of the other--see
Fig. 16. In fact, let us suppose that the positive
plate of capacitor 1 is connected to the ``input''
wire, the negative plate of capacitor 1 is
connected to the positive plate of capacitor 2,
and the negative plate of capacitor 2 is connected
to the ``output'' wire. What is the equivalent
capacitance between the input and output wires?
In this case, it is important to realize that the
charge Q

Cont..
• stored in the two capacitors is the same. This is most
easily seen by considering the ``internal'' plates: i.e.,
the negative plate of capacitor 1, and the positive plate
of capacitor 2. These plates are physically disconnected
from the rest of the circuit, so the total charge on them
must remain constant. Assuming, as seems reasonable,
that these plates carry zero charge when zero potential
difference is applied across the two capacitors, it
follows that in the presence of a non-zero potential
difference the charge +Q on the positive plate of
capacitor 2 must be balanced by an equal and opposite
charge -Q on the negative plate of capacitor 1. Since
the negative plate of capacitor 1 carries a charge -Q the
positive plate must carry a charge +Q .

• The potential drops, V1 and V2 , across the two
capacitors are, in general, different. However,
the sum of these drops equals the total
potential drop V applied across the input and
output wires: i.e.,V= V1 + V2. The equivalent
capacitance of the pair of capacitors is again .
Thus,
Cont..

What is electricity?
• Electricity is the set of physical phenomena
associated with the presence and flow of electric
charge. Electricity gives a wide variety of well-
known effects, such as lightning, static
electricity, electromagnetic
induction and electrical current. In addition,
electricity permits the creation and reception
of electromagnetic radiation such as radio waves.
• In electricity, charges produce electromagnetic
fields which act on other charges.

What is electric current?
• An electric current is a flow of electric charge. In
electric circuits this charge is often carried by
moving electrons in a wire. It can also be carried
by ions in an electrolyte, or by both ions and
electrons such as in a plasma.
• The SI unit for measuring an electric current is
the ampere, which is the flow of electric charges
through a surface at the rate of one coulomb per
second. Electric current can be measured using
an ammeter

Ohm’s law
• Ohm's law
• Ohm's law states that the current through a
conductor between two points is
directly proportional to the potential
difference across the two points. Introducing
the constant of proportionality,
the resistance,one arrives at the usual
mathematical equation that describes this
relationship:

Cont..
• where I is the current through the conductor
in units of amperes, V is the potential
difference measured across the conductor in
units of volts, and R is the resistance of the
conductor in units of ohms. More specifically,
Ohm's law states that the R in this relation is
constant, independent of the current

What is AC and DC?
• Direct current
• Direct current (DC) is the unidirectional flow
of electric charge. Direct current is produced by
sources such as batteries, thermocouples, solar cells,
and commutator-type electric machines of
the dynamo type. Direct current may flow in
a conductor such as a wire, but can also flow
through semiconductors, insulators, or even through
a vacuum as in electron or ion beams. The electric
charge flows in a constant direction, distinguishing it
from alternating current (AC). A term formerly used
for direct current was galvanic current.

Alternating current
• In alternating current (AC, also ac), the movement
of electric charge periodically reverses direction.
In direct current (DC, also dc), the flow of electric
charge is only in one direction.
• AC is the form in which electric power is delivered to
businesses and residences. The usual waveform of
an AC power circuit is a sine wave. In certain
applications, different waveforms are used, such
as triangular or square
waves. Audio and radio signals carried on electrical
wires are also examples of alternating current. In
these applications, an important goal is often the
recovery of information encoded (or modulated)
onto the AC signal.

What is resistor?
• Resistor
• A resistor is a passive two-terminal electrical
component that implements electrical resistance as a
circuit element. Resistors act to reduce current flow,
and, at the same time, act to lower voltage levels
within circuits. Resistors may have fixed resistances or
variable resistances, such as those found
in thermistors, varistors, trimmers, photoresistors,hu
mistors, piezoresistors and potentiometers.
• The current through a resistor is in direct
proportion to the voltage across the resistor's
terminals. This relationship is represented by Ohm's
law:

Resistivity
• The resistance of a given object depends primarily
on two factors: What material it is made of, and its
shape. For a given material, the resistance is
inversely proportional to the cross-sectional area;
for example, a thick copper wire has lower
resistance than an otherwise-identical thin copper
wire. Also, for a given material, the resistance is
proportional to the length; for example, a long
copper wire has higher resistance than an
otherwise-identical short copper wire. The
resistance R and conductance G of a conductor of
uniform cross section, therefore, can be computed
as

Cont..
• where L is the length of the conductor, measured
in meters, A is the cross-section area of the conductor
measured in square meters [m²], σ (sigma) is
the electrical conductivity measured in Siemens per
meter (S·m−1), and ρ (rho) is the electrical
resistivity (also called specific electrical resistance) of
the material, measured in ohm-metres (Ω·m). The
resistivity and conductivity are proportionality
constants, and therefore depend only on the material
the wire is made of, not the geometry of the wire.
Resistivity and conductivity are reciprocals:
• Resistivity is a measure of the material's ability to
oppose electric current.

Cont..
• The total resistance of resistors in series is
equal to the sum of their individual
resistances:

cont..
• The current in each individual resistor is found
by Ohm's law. Factoring out the voltage gives
• To find the total resistance of all components,
add the reciprocals of the resistances of each
component and take the reciprocal of the sum.
Total resistance will always be less than the
value of the smallest resistance

Cont..
• In electronics, a shunt is a device which
allows electric current to pass around another
point in the circuit by creating a low resistance
path.
• Use in current measuring. 50 A shunt resistor

Cont..
• An ammeter shunt allows the measurement
of current values too large to be directly
measured by a particular ammeter. In this
case the shunt, a manganin resistor of
accurately known resistance, is placed
in series with the load so that all of the
current to be measured will flow through it.

Cont..
• In order not to disrupt the circuit, the
resistance of the shunt is normally very small.
The voltage drop across the shunt is
proportional to the current flowing through it
and since its resistance is known,
a voltmeter connected across the shunt can
be scaled to directly display the current value.

Wheatstone bridge.
A Wheatstone bridge is an
electrical circuit used to measure
an unknown electrical resistance by
balancing two legs of a bridge
circuit, one leg of which includes
the unknown component. Its
operation is similar to the
original potentiometer.
Fig 6

Cont..
• In the figure, is the unknown resistance to be
measured; , and are resistors of known resistance
and the resistance of is adjustable. If the ratio of
the two resistances in the known leg is equal to the
ratio of the two in the unknown leg , then
the voltage between the two midpoints (B and D)
will be zero and no current will flow through
the galvanometer . If the bridge is unbalanced, the
direction of the current indicates whether is too
high or too low. is varied until there is no current
through the galvanometer, which then reads zero.

Cont..
• Detecting zero current with
a galvanometer can be done to extremely high
accuracy. Therefore, if , and are known to
high precision, then can be measured to high
precision. Very small changes in disrupt the
balance and are readily detected.

Derivation
• First, Kirchhoff's first rule is used to find the
currents in junctions B and D:
• Then, Kirchhoff's second rule is used for
finding the voltage in the loops ABD and BCD:

• When the bridge is balanced, then IG = 0, so
the second set of equations can be rewritten
as:
• Then, the equations are divided and
rearranged, giving:

Cont…
• From the first rule, I3 = Ix and I1 = I2. The desired value
of Rx is now known to be given as:
• If all four resistor values and the supply voltage (VS)
are known, and the resistance of the galvanometer is
high enough that IG is negligible, the voltage across
the bridge (VG) can be found by working out the
voltage from each potential divider and subtracting
one from the other. The equation for this is:

Cont..
where VG is the voltage
of node B relative to
node D.

Cont..
• The value of a resistor changes with changing
temperature, but this is not as we might expect, mainly
due to a change in the dimensions of the component as
it expands or contracts. It is due mainly to a change in
the resistivity of the material caused by the changing
activity of the atoms that make up the resistor.
• Materials which are classed as CONDUCTORS tend to
INCREASE their resistivity with an increase in
temperature. INSULATORS however are liable to
DECREASE their resistivity with an increase in
temperature. Materials used for practical insulators
(glass, plastic etc) only exhibit a marked drop in their
resistivity at very high temperatures. They remain good
insulators over all temperatures they are likely to
encounter in use.

Cont..
• The reasons for these changes in resistivity can be
explained by considering the flow of current through
the material. The flow of current is actually the
movement of electrons from one atom to another
under the influence of an electric field. Electrons are
very small negatively charged particles and will be
repelled by a negative electric charge and attracted by
a positive electric charge. Therefore if an electric
potential is applied across a conductor (positive at one
end, negative at the other) electrons will "migrate"
from atom to atom towards the positive terminal.

Cont..
• Only some electrons are free to migrate however.
Others within each atom are held so tightly to their
particular atom that even an electric field will not
dislodge them. The current flowing in the material
is therefore due to the movement of "free
electrons" and the number of free electrons within
any material compared with those tightly bound to
their atoms is what governs whether a material is a
good conductor (many free electrons) or a good
insulator (hardly any free electrons).

Cont..
• The effect of heat on the atomic structure of a material
is to make the atoms vibrate, and the higher the
temperature the more violently the atoms vibrate.
• In a conductor, which already has a large number of
free electrons flowing through it, the vibration of the
atoms causes many collisions between the free
electrons and the captive electrons. Each collision uses
up some energy from the free electron and is the basic
cause of resistance. The more the atoms jostle around
in the material the more collisions are caused and
hence the greater the resistance to current flow.
• In an insulator however, there is a slightly different
situation. There are so few free electrons that hardly
any current can flow. Almost all the electrons are
tightly bound within their particular atom.

Cont..
• In A material where the resistance increases with temperature
it is said that the material has A positive temperature
coefficient.
• When resistance falls with an increase in temperature the
material is said to have a negative temperature coefficient.
• In general, conductors have a positive temperature coefficient
• Whilst (at high temperatures) insulators have A negative
temperature coefficient.
• Different materials within either group have different
temperature coefficients. Materials chosen for the construction
of resistors therefore are most likely to be carefully selected
conductors that have A very low positive temperature
coefficient. In use, resistors made from such materials will
have only very slight increases in resistivity, and therefore
resistance, as temperature rises.

HEATING EFFECT OF ELECTRIC CURRENT: JOULE'S LAW
• The electric current in a conductor is due to the
motion of electrons. During their motion, electrons
collide with the oscillating positive ions in the conductor
and impart part of their energy to them. Ions oscillate
faster and their increased energy is manifested as heat.
The heat energy released in a conductor on passing an
electric current is called the “Joule heat” and effect is
called the ‘Joule effect”. The potential difference of V
volt applied between two ends of a conductor means
that V joule of electrical energy is utilized and converted
into heat when one coulomb charge passes through the
conductor. If Q coulomb charge passes through the
conductor in t seconds resulting in current I, the heat
energy produced is

Cont..
• W = V Q
= V I t
= I 2 R t ( Q V = I R according to Ohm’s law )
= ( V 2/ R )
The electric power, i. e., the electrical energy supplied per
unit time or converted into heat energy per unit time in a
resistance R, is
P = V I
= I 2 R
= ( V 2/ R
Thus, mechanical unit of energy, joule = watt. second which is
an electrical unit of energy. This being too small, kilowatt-
hour ( kwh ) = 3.6 × 106 joule is used as a practical unit of
electrical energy. R is the Ohmic resistance of the conductor
value of which does not depend upon V or I. Considering R as
a constant, P is proportional to I 2 or P is proportional to V 2.

Cont..
• Joule’s Law: - “The heat produced per unit time,
on passing electric current through a conductor
at a given temperature, is directly proportional to
the square of the electric current”.
To express heat produced in calories, the
following relation given by Joule is used.
W = JH
where W is mechanical energy in joule,
H is heat energy in calorie
and J = 4.2 joule / calorie is Joule’s constant or
mechanical equivalent of heat.

Electric power and energy
• Electric power is the rate at which electric energy is
transferred by an electric circuit. The SI unit
of power is the watt, one joule per second.
• Electric power is usually produced by electric
generators, but can also be supplied by sources such
as electric batteries. Electric power is generally
supplied to businesses and homes by the electric
power industry. Electric power is usually sold by
the kilowatt hour (3.6 MJ) which is the product of
power in kilowatts multiplied by running time in
hours.
• Electric power, like mechanical power, is the rate of
doing work, measured in watts, and represented by
the letter P.

cont..
Q is electric charge in coulombs
t is time in seconds I is electric
current in amperes V is electric
potential or voltage in volts.

Electrical energy
• When loosely used to describe energy absorbed or
delivered by an electrical circuit (for example, one
provided by an electric power utility) "electrical
energy" refers to energy which has been
converted from electrical potential energy. This
energy is supplied by the combination of electric
current and electrical potential that is delivered by
the circuit. At the point that this electrical potential
energy has been converted to another type of
energy, it ceases to be electrical potential energy.
Thus, all electrical energy is potential energy before
it is delivered to the end-use. Once converted from
potential energy, electrical energy can always be
described as another type of energy (heat, light,
motion, etc.).

What is thermocouple?
• A thermocouple is a temperature-measuring device
consisting of two dissimilar conductors that contact each
other at one or more spots. It produces a voltage when the
temperature of one of the spots differs from the reference
temperature at other parts of the circuit. Thermocouples are
a widely used type of temperature sensor for measurement
and control,and can also convert a temperature gradient into
electricity. Commercial thermocouples are
inexpensive,interchangeable, are supplied with standard
connectors, and can measure a wide range of temperatures.
In contrast to most other methods of temperature
measurement, thermocouples are self powered and require
no external form of excitation. The main limitation with
thermocouples is accuracy; system errors of less than one
degree Celsius (°C) can be difficult to achieve.

Cont..
• Any junction of dissimilar metals will produce an electric
potential related to temperature. Thermocouples for
practical measurement of temperature are junctions of
specific alloys which have a predictable and repeatable
relationship between temperature and voltage. Different
alloys are used for different temperature ranges. Properties
such as resistance to corrosion may also be important when
choosing a type of thermocouple. Where the measurement
point is far from the measuring instrument, the intermediate
connection can be made by extension wires which are less
costly than the materials used to make the sensor.
Thermocouples are usually standardized against a reference
temperature of 0 degrees Celsius; practical instruments use
electronic methods of cold-junction compensation to adjust
for varying temperature at the instrument terminals.

See back effect
• The conversion of temperature difference to electric current
and vice-versa is termed as thermoelectric effect. In 1981,
Thomas Johann See beck found that a circuit with two
dissimilar metals with different temperature junctions would
deflect a compass magnet. He realised that there was an
induced electric current, which by Ampere's law deflect the
magnet. Also electric potential or voltage due to the
temperature difference can drive the electric current in the
closed circuit.
• To measure this voltage, one must use a second conductor
material which generates a different voltage under the same
temperature gradient.

Cont..
• V- Voltage difference between two dissimilar metals
• a- Seebeck coefficient
• Th - Tc - Temperature
difference between hot and cold junctions
•
• There are three major effects involved in a thermocouple
circuit: the Seebeck, Peltier, and Thomson effects.
• The Seebeck effect describes the voltage or electromotive
force (EMF) induced by the temperature difference (gradient)
along the wire. The change in material EMF with respect to a
change in temperature is called the Seebeck coefficient or
thermoelectric sensitivity. This coefficient is usually a
nonlinear function of temperature.
•

References-Images
• https://www.google.co.in/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=
0CAcQjRw&url=http%3A%2F%2Fphysics.bu.edu%2F~duffy%2FPY106%2FElectricfield.html&ei=-
JSjVMS9PIzhuQSvkIHACQ&bvm=bv.82001339,d.c2E&psig=AFQjCNHRlFXJqrWpUJ1EGD9TstY_M64J
Mw&ust=1420092690355196
0CAcQjRw&url=http%3A%2F%2Fimgarcade.com%2F1%2Fcapacitor-
symbol%2F&ei=kJWjVMXXC4vmuQSl-
IKIBQ&bvm=bv.82001339,d.c2E&psig=AFQjCNFmUEosk32DchE1jsUeATwfj95qeA&ust=142009317
3981775
0CAcQjRw&url=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FDielectric&ei=UZajVOurG4KzuATIiYL
QAw&bvm=bv.82001339,d.c2E&psig=AFQjCNFOooTuOPV7WixunoloNKLyWUr3aQ&ust=14200933
78519694
0CAcQjRw&url=%2Furl%3Fsa%3Di%26rct%3Dj%26q%3D%26esrc%3Ds%26source%3Dimages%26c
d%3D%26cad%3Drja%26uact%3D8%26ved%3D0CAcQjRw%26url%3Dhttp%253A%252F%252Fww
w.learningaboutelectronics.com%252FArticles%252FCapacitor-charge-
calculator.php%26ei%3D6ZijVJWrNtGiugSIh4HwCQ%26bvm%3Dbv.82001339%2Cd.c2E%26psig%3
DAFQjCNEtOhL5sGu3jt8ymQ0TtsGHSLj7Nw%26ust%3D1420093963260726&ei=6ZijVJWrNtGiugSI
h4HwCQ&bvm=bv.82001339,d.c2E&psig=AFQjCNEtOhL5sGu3jt8ymQ0TtsGHSLj7Nw&ust=1420093
963260726

• https://www.google.co.in/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rj
a&uact=8&ved=0CAcQjRw&url=http%3A%2F%2Fmysite.avemaria.edu%2Fjcdaly%2
Fphys223%2Flab%2FLab3RCcircuits%2FRCcircuitsPart2.html&ei=4JqjVNP_F4qTuAS
7joDQCQ&bvm=bv.82001339,d.c2E&psig=AFQjCNH_d4ctxGgOxBBVkbxNwvcFqgp8
bg&ust=1420094487687656
• https://www.google.co.in/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rj
a&uact=8&ved=0CAcQjRw&url=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FWhe
atstone_bridge&ei=4KWjVP-
nIcSTuASQ_YKABw&bvm=bv.82001339,d.c2E&psig=AFQjCNGWzdd4-i7-
cXKGXerrwUNxt_iW3A&ust=1420097380016548

REFERENCE
• B.L.Theraja, “Electrical Technology Vol.1”, S.Chand
Publication.
• D.P.Kothari, “Basic Electrical Engineering”, Tata
McGraw-Hill publication.
• U.A.Patel “Circuits and Networks”.

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