MCB

Miniature Circuit Breaker

Maximum Power Transfer Theorem

Millman'sTheorem

Youtube link

https://youtu.be/15m3tC5fPYM

Superposition Theorem

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#Superposition_Theorem
It states that for a bilateral linear system having more than a independent sources, voltage/current in any branch (when all independent source are working together) equals the algebric sum of the voltages/ currents by each independent source acting alone, where all other sources are replaced by their internal impedance.
:
Eliminating voltage source with their internal impedance where Z = zero for ideal case , short circuit
Eliminating current source with their internal impedance where Z= infinity for ideal case, open circuit.

Youtube link https://youtu.be/MTuRjxqvHgI

KCL and KVL

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Gustav Robert Kirchhoff (
12 March 1824 – 17 October 1887) was a
German physicist who contributed to the
fundamental understanding of electrical
circuits by his two laws , spectroscopy, and the emission of
black-body radiation by heated objects.

Independent Source and Dependent Source

Today we discuss about Sources, Electrical Sources.

Electrical Source: who provides enrgy to do some workdone.
There are two type of sources.
¡) Independent Source
¡¡) dependent source

Independent Source:  Those Voltage or current source, which do not depend on any other quantity in the circuit.

Dependent Source: a dependent voltage or current source is one which depends on some other quantity in the circuit which may be either a current or voltage source. It is represented by diamond-shaped symbol to avoid confusion with independent source.
4 possible dependent sources are-
   A) Voltage dependent Voltage source/ Voltage controlled Voltage source[ VCVS]
   B) Voltage controlled Current source
   C) Current controlled Voltage source
   D) Current controlled Current source

Independent sources exist as a battery, a dc generator and an alternator etc. And you know little or more about that.
But dependent sources are parts of models that are used to represent electrical properties of electronic devices such as operational amplifiers and transistors etc.
example of dependent sources are operational amplifiers, BJT ,MOSFETs, Voltage and Current regulator , Piezoelectric device etc.

VCVS- A dependent source depends on an input to determine output. For example, A vcvs's input tells it what the output should be.
Gain is Vout/Vin. If gain=1
Vout= Vin

VCCS- here gain= I(out)/ V(in).
vcvs has a constant of propotionality called transconductance(gm).
Unit is Siemens.

CCVS- here gain= V(out)/ I(in)
Unit is Ohn. ccvs has a constant of propotionality called trans resistance.

CCCS- has a constant of propotionality called Current gain.
gain = I(out)/ I(in).

Circuit's Word

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Circuit's Word

Circuit-
     A circuit is a closed conducting path through which current flows or tends to flow when a potential is applied.

Parameters-
               Resistance, Capacitance, Inductance etc.
These parameters may be lumped or distributed.

Lumped- The elements building a lumped system are thought of being concentrated at singular points. e.g. currents and voltage (those are functions of time only)

Distributed- The elements in distriuted system are thought of being distributed in space, so that physical quantities depends on both time and space. e.g. electrical line where L,C, R are not constant and function of time and length both.

Linear Circuit- The parameters of linear circuit is constant with time, Voltage and Current and circuit obeys ohm's law.

Non-linear Circuit- Its parameters change with voltage and current.

Bilateral Network- It behaves same in both direction. The transmission line is bilateral in nature. It can perform it's function equally well in both direction. A network consisting only resistances is good example of bilateral network.

Unilateral Network- A circuit whose operation, behavior is dependent on the direction of the current through elements is called unilateral network.

Passive network and Active Network-
     An active network is a network that contains an active source- voltage source or current source. A passive network is a network that does not contain an active source.

Node & Junction -
                   Node is refers to any point on a circuit where two or more circuits elements are connected together. Whereas Junction is that point where electrical conductors are joined electrically. For two nodes to be different, their voltages must be different. A conductor with a sustantially zero resistance is considered to be a node for the purpose of analysis. Whereas junction is a collection of conductor at the same emf.

Loop & Mesh -
       A loop is a closed path in a circuit where two nodes are not repeated twice except the initial point. But in a loop other paths can be included inside.
      A mesh is closed path in a circuit with no other paths inside it. In other words, a loop with no other loops inside it.

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Current Divider Rule and Voltage Divider Rule

When Current flows through two parallel circuit, it is divided according to their path resistance. This is the basic funda of current divider rule. Like CDR, Voltage drop in resistance in a series circuit happens according to their resistance, that is voltage divider rule.
Follow Picture.

Nonlinear Resistor

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Before we proceed, We should have clear view about linearity.
What is linearity?
A graph which holds linear graphical picture i.e how current changes due to voltage, Its linearity.
Then what is linear resistor?
When output is propotional to Input, i.e linear condition. When a resistance resists current to flow in presence of a electrical potential force, we call it a kind of electric circuit. Here input is voltage and output is current.
Now, If we get linear graphical picture of V-I curve, then we say, that element is linear resistance.

Those elements whose V-I curves are not straight lines are called nonlinear elements because their resistance are nonlinear resistance e.g. incandescent lamp, varistors , thermistors and diodes etc.

Incandescent lamps :
Let me explain with an example. The cold resistance of a 100 w incandescent lamp is about 9.5 ohms. If that resistance stayed same with 120 V potential applied, according [like us on facebook]to ohm's law, the bulb would draw about 12.5 amp with 1500 watt(power dissipation). But hot resistance of tungsten becomes 144 ohms(15 times the cold resistance). The resulting current is 0.83 amps with 100 watt(power dissipation). So here we come to the conclusion that when tenperature is increased, resistance increases highly.

Varistors :
A varistors is an electronic component with an electrical resistance that varies with the applied voltage. It is a voltage dependent metal-oxide material whose resistance decreases sharply with increasing voltage. There is a corresponding rapid decrease in resistance when the current increases. So it is used to provide over voltage protection.
The zinc-oxide based varistors are primarily used for protecting solid-state power supplies from low and medium surge voltage in the line. And silicon-carbide varistors provide protection against high-voltage surge.

Thermistors:
   A thermistors is a type of resistors whose resistance is dependent on temperature, more so than in standard resistors. Thermistor is made of metallic oxides in a suitable binder and has a large negative coefficient of resistance i.e its resistance decreases with increase in tempt.

Diodes:
    In electronics, a diodes is a two-terminal electronic component that conducts primarily in one direction, It has low resistance to the current in one direction and high resistance in the other. It has also a non-linear graph. When voltage continue increases, current increases high suddenly.
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Basic Idea of Temperature Coefficient and increase/decrease in resistance due to Temperature

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A resistor's  tempt. coefficient of resistance tells you how much its value changes as its temperature changes.
unit = ohm /ohm°C

                   #Check_Fig_here.

R(0) = Resistance of the material at 0°C
R(t) = Resistance of the material at t°C

Increase in Resistance depends upon
¡) initial resistance
¡¡) rise in tempt.
¡¡¡) on thr nature of the material.

#Alpha signs denotes temperature co-efficient of resistance normally.

wiki source :
Alpha (uppercase Α , lowercase α; Ancient Greek :
άλφα, álpha , modern pronunciation álfa ) is the
first letter of the Greek alphabet . In the system
of Greek numerals it has a value of 1. [dont forget to like, follow and support facebook.com/thecurrentblogelectrical for more]

α=[ dR/ R(0) ]x t
where dR = R(t) - R(0)

Theoretically, at -t tempt., the resistance should be vanished, but in actual at-234.5°C (easy to remember,look again), it never meet zero, it departs from a straight line at very low tempt.
see figure.
So The second part now.

Question is, Why does electrical resistance increase as tempt. increases?
- Resistance of the conductor changes with change in size of the conductor as well as temperature.

Some says, as tempt. increases, the dimension of the conductor will expands or contracts and that is the reason behind change of resistance in material. It is actually misconception.
lets read! Those material,about which, we are talking in this post are classified into two groups
1. Resistance increases with increase in temperature.
2. Resistance decreases with increase in tempt.
Most of the metals are belongs to the the first one and insulators are from second.
The reasons for these changes can be explained by considering the flow of current(actually electron) through that material. Electron are negatively charged particles and will be attracted by positive atoms and repelled by negative charged electrons. So when a electric potential is applied, the free electrons tends to flow into the material and start to flow in time. Now Temperature is increased.
The effect of increase in temperature in material is to make the atoms vibrate and vibrate violently as tempt increases more. In a conductor which already has large amount of electron will make collision between electrons and vibrated atom. As a result, some kinetic energy of electron may fall and that vibration [ dont forget to like and follow and support us facebook.com/thecurrentblogelectrical for more] increases the resistance of that metal body.
Whereas, in insulators free electrons are quietly less than metal. Almost all the electrons are tightly bound within their particular atom. Increase in tempt. sufficiently vibrates the atoms and enough to actually shake some of the their captive electrons free.
So the resistance of Insulator material falls due to increase in tempt.
I have a question for you here.
What happen to electrolyte when tempt. increase? tell us in comment section.
P.S.
In a material where the resistance increases with an increase in tempt., the material is said to have a POSITIVE TEMPERATURE COEFFICIENT( e.g. Copper Cu).
When resistance decreases with an increase in tempt., the material is said to have a NEGATIVE TEMPERATURE COEFFICIENT(e.g. Semi-Conductors).

Important Resistor Materials

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Tungsten
W-wolfram Atomic Number-74

1. Hard Metal

2. It can be drawn into very thin wires.

3. Melting point 3422°C

4. Used as filaments in incandescent lamps, and in electron tubes and also in heater.

Carbon
C atm no 6
Graphite 90% of carbon coal coke charcoal etc

1. High resistivity about 4600 micro ohm.cm

2. Negative tempt. Coefficient of resistance.

3. Pressure sensitive resistance material and has low surface friction.

4. This oxidised at about 300°C and is very weak.

5. Used as brush in electrical machines.

6. As components in electronics and communication equipments.

Nichrome
Nickel 75-78% chromium 20-30% manganese 1.5% and iron(balance)

1. Its resistivity is high.

2. Temperature coefficient of resistance is low.

3. Withstands high tempt for a long time.

4. Used as electric iron coil, furnace and heating elements.

Manganin
Copper 80% manganese17-18% nickel 1.5-2%

1. Resistivity 0.49 to 0.50 micro ohms.m

2. Low tempt. Coefficient of resistance(0.00015)

3. Melting point is 1020°C

4. Specific gravity is 8.19

5. Used for instruments shunts and for standard resistance.

Constantan
Copper 60% nickel 40%

1. It does not rust or corrode due to air , heat and moisture.

2. Resistivity is 49 micro ohm.cm

3. Specific gravity is 1.9

4. Melting point is 1300°C

5. Used for different types of rheostats, resistance wires, resistance boxes, arc lamps, motor starters, supporting wires for electric filaments.

Platinum
Pt atm no 78

1. It is non corroding.

2. Resistant to most chemicals.

3. Can be drawn into thin wires and strips.

4. Melting point 1775°C

5. Resistivity 10.5 micro ohm.cm

6. No oxidation.

7. Used for heating element in laboratory ovens and furnaces.

8. Used for platinum-rhodium thermocouples measurement of upto 1600°C.

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What will happen if DC is provided to primary of transformer?

Basically, transformer windings
are designed with specified value of impedence
that they have, now most part of the impedence
is contributed by inductance. In case of DC we
dont have capacitive and inductive effect in
concern anymore, the only opposition to the flow
is made by resistance which is small. Now high
currents will flow through the primary windings
and windings will burn out. They do so because
they are designed for ac specification in case of
dc they can't handle such high currents due to
less resistance offered.