EMTL QUESTIONS

UNIT –I
 
1.       Write the Poisson’s and Laplace equations?
2.       Differentiate conductors and Insulators.
3.       Explain about Gauss law?
4.       Explain about Maxwell tow equation for the electrostatic filed?
 UNIT II
 
1.       Define Biot-Savart law? How it will useful to derive H? Explain?
2.       State and explain the boundary conditions of the electric and magnetic fields.
3.       State Ampere’s circuit law?
  UNIT III
 
1.       What are the wave equations for a lossless medium and a conducting medium
2.       Explain oblique incidence wave propagation with perpendicular polarization.
3.       Prove that E&H reflected waves are standing waves when uniform plane wave
4.       incident normal to the free space and conductor boundary surface?
5.       Explain about types of polarizations and tis applications?
6.       Explain about Skin depth ?
 UNIT   IV
 
1.       What is pointing theorem? Derive the expression for pointing vector.?
2.       Explain about  the electric field boundary conditions between dielectric and conductor?
 
  UNIT V
Derive the primary & secondary constants for a low loss transmission line?
3.       Explain about the parameters of Transmission line ?
4.       Explain about Transmission line equation and its parameters?
5.       Explain about transmission characteristic impedance?
 UNIT VI
 
1.       Explain Quarter wave and Half wave Transmission Line.?
2.       Expain about Low loss radio frequency lines and UHF Transmission lines?
3.       List out applications of smith’s chart. How to measure them?
 
 
 
 

RANDOM VARIABLE

Introduction: The basic to the study of probability is the idea of a Physical experiment. A single performance of the experiment is called a trial for which there is an outcome. Probability can be defined in three ways. The First one is Classical Definition. Second one is Definition from the knowledge of Sets Theory and Axioms. And the last one is from the concept of relative frequency.

Experiment:

Any physical action can be considered as an experiment. Tossing a coin, Throwing or rolling a die or dice and drawing a card from a deck of 52 cards are Examples for the Experiments.

Sample Space: The set of all possible outcomes in any Experiment is called the sample space. And it is represented by the letter s. The sample space is a universal set for the experiment. The sample space can be of 4 types.

 They are: 1. Discrete and finite sample space.

2. Discrete and infinite sample space.

3. Continuous and finite sample space.

4. Continuous and infinite sample space.

Tossing

a coin, throwing a dice are the examples of discrete finite sample space. Choosing randomly a positive integer is an example of discrete infinite sample space. Obtaining a number on a spinning pointer is an example for continuous finite sample space. Prediction or analysis of a random signal is an example for continuous infinite sample space.

Event:

An event is defined as a subset of the sample space. The events can be represented with capital letters

like A, B, C etc… All the definitions and operations applicable to sets will apply to events also. As with sample space events may be of either discrete or continuous. Again the in discrete and continuous they may be either finite or infinite. If there are N numbers of elements in the sample space of an experiment then there exists 2N number of events.

The event will give the specific characteristic of the experiment whereas the sample space gives all the characteristics of the experiment.

OSCILLATOR

It is a electronic circuit which produces oscillations. Essential requirements of an oscillator  A resonant circuit or a crystal which decides oscillatory frequency of an oscillator circuit is called tank circuit. Damped oscillations  Oscillations whose amplitude goes on reducing continuously are called damped oscillations. This type of oscillations are produced by sparking.

Types of Oscillator Circuits

 Ticker feedback, oscillator oscillator

 1.Hartley series fed and Hartley parallel fed oscillator

2.Colpitts :     It is an oscillator, which employs a crystal in place of LC lank circuit. It is renowned as a stable frequency oscillator. Employs capacitive feedback oscillator

•  Tuned Plate Tuned Grid (TPTG) oscillator
•  Electron coupled oscillator
•  Master oscillator power amplifier (MOPA) oscillator
•  Crystal oscillator
•  Multivibrator oscillator
•  Wein bridge oscillator
•  Neon lamp oscillator
•  Thyratron sweep oscillator
•  Phase shift RC oscillator
•  Beat frequency (BFO) oscillator
•  Klystron oscillator
•  Magnetron oscillator.

Classification of Amplifiers

1. Class ‘A’ amplifier : The amplifier circuit in which control-grid/base bias and signal voltages are adjusted in such a way that current in the output circuit flows for the entire duration of the input signal. This type of circuit has best fidelity, minimum distortion but low output power.
2. ‘B’ amplifier : It is the amplifier circuit in which control-grid/base sias and signal voltages are adjusted in such a way that current in the output circuit flows for less than half time of the input signal. This type of circuit has, minimum fidelity, maximum distortion but maximum output power .  These are used in push-pull audio stages . 
3. Class ‘AB’ amplifier : It is the amplifier circuit in which control-grid/base bias and signal voltages are adjusted in such a way that current in the output circuit flows for less than full but more than half time of the input signal.This type of circuits are utilized in ordinary type of equipments. Their efficiency is 35-50%. :
4. Class ‘C’ amplifier : It is the amplifier in which control-grid/base bias and signal voltages are adjusted in such a way that current in the output circuit remains for less than half time of the input signal. This type of circuit has, minimum fidelity, maximum distortion but maximum output power too. These are used for RF amplification in transmitters.
 

Coupled amplifiers

 Coupling methods
Used for inter stage coupling of two amplifier stages are: 1. RC coupling method : Coupling employing two resistors mid a capacitor as coupling elements is called RC coupling. One resistor acts as a load resistor of first stage and a capacitor feeds the signal to the following stage. Second resistor is used to provide u-discharging, path for the DC charge stored in the capacitor. This type of circuit remains Tree from ‘direct pickups of radio waves defect.
2. Impedance coupling method : It is a modified form of RC coupling in which an inductive load is used in place of resistive load. The overall gain of an impedance coupled amplifier is higher than that of a RC coupled amplifier.
3. Transformer coupling method : It is a coupling employing a transformer as a coupling element. The primary of the transformer acts as an inductive load of the first stage and secondary acts as a signal source for the following stage. In this method, two amplifier stages remain isolated with each oilier to the DC source.
4. Direct coupling method : It is a coupling without using any coupling element. This method of coupling is distortionless and gives a uniform response over wide frequency range.

Direct coupling amplifier

FEED BACK AMPLIFIER

If the feedback signal is of opposite polarity to the input signal, then the negative feedback results. While
negative feedback results in reduced overall voltage gain, following improvements are obtained, :
(a)Higher input impedance
(b) Better stabilized voltage gain
(c) Improved frequency response
(d) Lower output impedance
(e) Reduced noise
(f) More linear operation
Types of Feedback Connections.
(i) Voltage -series feedback
(ii) Voltage - shunt feedback °
(iii) Current - series feedback
(iv)Current - shunt feedback.

AMPLIFIER CLASSES

One method generally employed to categorize amplifier is by class which basically represent the mount of output signal varies over one cycle of "operation for a full cycle of input signal.

1.Class A : The amplifier circuits which falls into this category are linear as these operate in a small

region in the middle of the load line.

2. Class B : This amplifier circuit provides an output signal varying over one-half the input signal cycle.

Class ration creates a very distorted output Bee ton of the input takes place for only _ 180° of the output signal swing. Power efficiency ‘of class-B is more than that of Class-A.

Classification of Amplifiers

 According to frequency range.

1. DC(Direct coupled ) amplifiers: From zero frequency dc on wards.

2.Audio frequency amplifiers : 20Hz to 20kHz

3.Video Frequency amplifiers : up to few MHz

4.Radio frequency (RF) amplifiers : From a few kHz to hundreds of MHz.

5. Ultra high frequency (UHF) and Microwave amplifiers: Upto hundred or thousands of MHz,

According to Method of operation.

The position of the zero signal (quiescent) operating point and the extent of characteristic curves being used determine the category of operation. Thus amplifiers (using either BJT or FET) may be  classified as class A, class AB, class B or class C  amplifiers as per following definition.

(1).Class A amplifiers.: In these operating point and the input signal magnitude are so selected that the output circuit current (collector current or drain current) flows all the time (for full cycle of the a.c. signal). A class A amplifier operates essentially over the linear portion of characteristic curves of the device.

(ii) Class B amplifier. In-these operating point is placed at an extreme end of its characteristic curve with the result that zero signal current (or zero signal voltage) is almost zero. Hence zero signal output power is very small. Witha sinusoidal input signal voltage, amplification takes place for only half the cycle. Thus if output circuit quiescent current is zero, on application of signal, the output current remains zero for half the cycle and flows for the remaining half cycle.

(iii) Class AB amplifier. In these operation lies in between class A and class B operations. Thus in a class AB amplifier, output current flows for more than half but less than the complete cycle of input sinusoidal signal.

(iv) Class C amplifier. In these operating point is so chosen that the output current flows for less than one-half of the input sinusoidal signal cycle.

FIELD EFFECT TRANSISTORS (FET)

Field effect transistor. Operation depends on the flow of majority carriers only. So , itis a unipolar device. No minority carrier current.  In N channel FET : Width of space between P regions is controlled by varying gate voltage (Controlled by gate-to- source potential),

Advantages :

1. Easy / Simpler to make

2. High input impedance (Mega Q)

3. High power gain

4.Less noisy

5.No offset voltage at zero drain current

RECTIFIERS

It is conversion of an Alternating current into Unidirectional current,

Types of rectifiers are :

1.Haf wave Rectifier

2. Full wave Rectifier

3. Bridge Rectifier

Half-wave rectifier circuit :

It provides DC output for positive half cycles only: Maximum rectification efficiency of a half  wave

Full-wave rectifier;

It provides DC output  for both half cycles of Ac.

Advantages:

1. High efficiency.

2.Ordinary filter circuit is sufficient 

3.Provides more output current

Bridge Rectifier

It is a transformer less full wave rectifier. it requires 4 diodes.

Advantages:

Full-wave rectifier (two diodes type) requires a transformer with centre-tapped secondary, whereas, bridge rectifier does not require such transformer. 

1, Diode valve rectifier

Diode valve is a two electrode vacuum tube which consists of a cathode and an anode. When cathode is heated up by passing a current through it filament, it starts to emit electrons. Anode emitted electrons if it is made positive with re to cathode. If AC is applied to anode, then a current will flow for each positive half cycle only. In this way, AC will be converted into DC. Silicon diode is better tor the rectification of AC.

2. Metal rectifier:

similarly 

So, electric current can flow easily from a sharp edged point towards a flat surface even across a thin layer of an insulation.

Type of Metal rectifiers:

(1) Selenium rectifier

(2) Copper oxide rectifier

Zener Diodes

These diodes are designed to operate in the break down region without damage. It is specified by its break down voltage and maximum power dissipation.

ANODE | ‘ CATHODE

                     Circuit symbol of a zener diode 

Zener Breakdown!

It is a type of breakdown observed in a reverse biased p- n junction that has very high doping concentration on both-sides of the junction. The build-in-field is high and the depletion layer narrow as a result of high level of doping.

Transistor Characteristics

These are studied by plotting IE-VE and IC-VC curves,

(1) IE-VE curves : It show that emitter current,depends on the emitter yoltage and the collector. voltage

 has a very little effect on the emitter current and hence transistor has a low input impedance,

2)IC-VC curves : It show that a transistor attains a high collector current at a low collector voltage and 

 hence the transistor has a high output impedance.

Current gain Alpha ()

 It is ratio of the collector current variations to the emitter current variations on no-load and constant

 voltages

where, IC = collector current variations

IC = emitter current variations

Note : Both current variations should be measured in

the same units.

(2) Beta (B)

It is ratio of the collector current variations to the base current variations on no load and constant voltages.

where, I, = base current variations. Relation between a and B

   Alpha cut-off frequency

The frequency at which gain of a transistor is reduced to 10.1% of its gain at low frequency is called alpha cut-off frequency of the transistor.

Voltage gain of a transistor It is ratio of the output voltage to the input voltage

V, _ Output voltage

VG.= + = Tnput voltage

Power gain of a transistor é It is ratio of the output power to the input power

Output power _ Py

PG-= Toput power P,

Three Basic configurations of Transistors 

There are three basic configurations of transistors.

1. Common base (CB) configuration :

It is the transistor circuit in which base is kept common to the input and output circuits.

Characteristics

() Low input impedance (50 to 500 ohms).

(i) High output impedance (1 to 10 mega ohms)

(iii) Current gain alpha = Jess than unity.

 2.Common emitter (CE) configuration

It is the transistor circuit is which emitter is kept common to the input and output circuits.

Characteristics of CE

() High input impedance (500 to 5000 ohms)

(i) Low output impedance (50 to 500 kilo ohms)

(ii) Currem gain, fis = upto 98

(iv) Power gain uplo 5000 or 37 dB.

(vy) 180° out of phase output.

3, Common collector circuits (CC) configuration

Itis the transistor circuit in which collector is kept common to the input and output circuits.

It is also called emitter follower

Characteristics

() High input impedance (150 to 600 kilo ohms)

(i). Low output impedance (100 to 1000 ohms)

(ii) Current gain, pi = 99

(iv) Voltage and power gain is equal to or less than unity.

FET (Field Effect Transistor)

It is a solid state device in which conduction of: is controlled by an electrostatic field. Its

are called source, drain and gate.

Transistor Data

It is a reference book which contains information regarding characteristics of tr:

(I) Maximum collector-emitter voltage

(i) Maximum collector current

(iii), Leakage current

(iv) Input output impedances

(v) Current gain and power gain

(vi) Alpha cut off frequency

(vii) Power dissipation

(viii) Working temperature

(ix) Collector-base voltage and cap

(x) Base current ete,

Transistor Manufacture

Many transistors or other elements, their interconnecting links, are made ¢ to turn it into an IC, I usual

 method of of monolithic ICs (mono=single, case silicon) has many similarities

SWITCHES

A switch is used in an electric circuit as a device for making or breaking the electric circuit. switches may be classified as 

1. Oil switches: These are usually use  voltage heavy current circuits,

2. Air switches : These are further classified into

(a) Air-break switches

(d) Isolators

(o) Disconnected switches

BUS- BAR ARRANGEMENTS

Bus-bars are arranged to achieve

(a)dequate operating flexibility

(b) sufficient reliability

(c) minimum cost.

The cost can be minimised by reducing the number of  circuit breakers to a minimum but complication

 of  the protective gear are increased.  Some bus-bar arrangements.  

(1) Single bus-bar arrangement. In this arrangement a set of bus-bars is used for complete power station and to this bus-bar are connected all generators, transformers and feeders through circuit breakers and isolating switches. Such a bus-bar arrangement is cheaper in initial as well as in maintenance cost  and simple in operation and relaying.

(2) Single bus- bar system with sectionalization . With increased number of generators and outgoing

feeders connected to the bus-bars, it becomes essential to provide arrangement for sectionalizing the bus-bars so that a fault on any one section of the bus-bars may not cause a complete shutdown. ‘This is achieved by providing a circuit breaker and isolating switches between the sections.

(3) Ring bus-bar system. In this arrangement each feeder is supplied from two paths, so that in case of failure of a section, supply is not interrupted.  

(4) Duplicate bus-bars system. Duplicate bus-bar system with sectionalization is usually adopted in order to maintain continuity of supply. Such a system consists of two-bus-bar couplers and sectionalizing breaker converts the duplicate bus- bars into a ring system having greater flexibility.

TYPES OF DIODES

 

1. Zener diodes 

In zener region, the characteristic d™ potential almost vertical manner at a reverse : conduction denoted V , For Zener diode ,direction of co de. Si is of current is reversed to that of simple it a. Ss preferred in manufacturing of Zener diode higher temperature and current capability.

2. Light emitting diode (L.E.D) : When a junction diode is forward biased, energy is released at junction in the form of light due to recombination of electrons and holes. In case of Si or Ge diodes, the energy ereleased in the infra-red region.  In the junction diode made of GaAs, InP etc energy is released in visible region such  a junction diode is a light emitting diode (LED). Its symbol

Solar cell : Solar cell is a device for converting solar energy into electrical energy. Ajunction diode in which one of the P or N sections is made very thin (so that the light energy falling on diode is not greatly absorbed before reaching the junction can be used to convert light energy into electric energy such diode is called as sola cell. Its symbol is

3.Tunnel diode.

An pn junction diode has an impurity concentration of about 1 part in 10°. With this amount of doping the width of the depletion region which constitutes a potential barrier at the junction, is of the order of a micron. This potential barrier restrains the flow of carriers from the side of the function where they constitute majority carriers to the side where they constitute minority carriers. If the concentration of impurity atoms is greatly increased say to 1 part in 10° the device  characteristics are completely changed.

SOME SPECIAL DIODES

Photodiode : A kimctopm diode made from “light or photo sensitive semiconductor’ is called photo  diode.

Its sysmbol is SS When light of energy “hv” falls on the photodiode (here hv > energy gap) more electrons move from valence band to conduction band, and due to this current in circuit of photodiode  in reverse bias, increases. As light intensity is increased, the current goes on increasing so photodiode : photo diode is used, to detect light intensity.

                                                                            Diode symbole.

Types of Generators

 

                                                                 (1) Permanent magnet

                                                                       (2.)Self-excited 

                                                                 (3) Separately excited,

MOTOR

It is a machine which converts mechanical energy, into mechanical energy.

 

    

 

 

 

 

 

   

 

 

 

 

 

   

 

Types of semiconductors.

1) n-type semiconductors

semiconductors are formed elements from Vth group ¢ As and Sb. Addition of a percent of such elements may increase the conductivity by several powers of ten. Ag the impurity increases the ionization  energy decreases.

(2) p-type semiconductor p-type

semiconductors are formed by doping with element from the third group, ie. B, Al, Ba, In. At absolute  zero, the holes remains bound to the impurities, but as the temperature is increased, valence electrons may  be excited into the bound holes with the result that holes are created in the valence band.  At low temperature conductivity results  predominantly from holes produced by excitation  of valence  electrons into acceptor levels.

SEMICONDUCTORS

 SEMICONDUCTORS. :
Now consider materials, which are neither insulators nor conductors. Such materials are called 
semiconductors. The forbidden gap is very narrow about 1 eV. In such materials, the energy provided by the heat  at room  temperature is sufficient to lift the electrons from the valence band to the conduction band.  Therefore at room temperature, semiconductors are capable of conduction, But at 0°K or absolute zero  (-273° C), all the electrons of semiconductor materials find themselves locked in the valence band.  Hence at 0°K, the semiconductor materials behave as perfect insulators. In case of semiconductors,  forbidden gap energy depends on the temperature.

For silicon and germanium, this energy is given by, Eg = 1.21-3.6 x 10+ x T eV (for Silicon)

                                                                                   Eg = 0.785 — 2.23 x 104 x T eV (for Germanium)

where, T = absolute temperature in °K     Assuming room temperature to be 27° C, 

i.e. 300 °K, the forbidden gap energy for Siand Ge can be calculated from the above equations. The

forbidden gap for the germanium is 0.72 eV while for the silicon it is 1.12 eV at room temperature. The 

silicon and germanium are the two widely used semiconductor materials in electronic devices. At room 

temperature, the materials classified as semiconductors have a resistivity between that of a typical metals 

and that of a typical insulators, However resistivity of semiconductors in general depends  strongly on 

temperature. This classification is not satisfactory because at very low temperature, semiconductors may 

behave as insulators,

INSULATORS

In case of such insulating material, there exists a large forbidden gap in between conduction band and the valence band. Practically it is impossible for an electron to jump from the valence band to the conduction band. Hence such materials cannot conduct and called insulators.

 The forbidden gap is very wide, approximately of about 7 eV is present in insulators. For a diamond, which is an insulator, the forbidden gap is about 6 eV. Such materials may conduct only at very high temperatures or if they are subjected to high voltage. Such a conduction is rare and is called breakdown of an insulator. 

The other insulation materials are glass, wood, mica, paper etc. The insulating materials used in electrical engineering may be gases, liquids, solids or vacuum.
Gases that serves as dielectrics are air, nitrogen, hydrogen, sulphur hexafluoride ete. Liquid dielectrics that are commonly used are mineral oils, synthetic hydrocarbons, etc. and they are used not only as  insulating media but also to improve heat conduction property of apparatus.
          Solid insulators are extremely diverse in origin and properties, they may be natural organic substances like paper, cloth, rubber etc. or inorganic materials like mica, glass and ceramic or synthetic materials like plastics.
Dielectric materials provide electrical insulation between conductors and also acts as stores of electrical charges.

What is conductor ?

A). A material having large number of free electrons can conduct very easily.

Example: Copper has 8.5X10 power 28 free electrons per cubic meter which is very large number. Hence copper is called good conductor. In fact  in the materials like copper ,aluminum there is no forbidden gap between valence band and conduction band. the two bands overlap. Hence even at room temperature , a large number of electrons are available for conduction .So without any additional energy , such metals contains a large number of free electrons and hence called good conductor.