bel model questions & answers - infonics · 2016. 2. 26. · ec100: basics of electronics...

1 BEL Model Questions & Answers

Muhammed Riyas A.M,Assistant Professor,Dept. of ECE,MCET Pathanamthitta

Model Questions and Answers

EC100: Basics of Electronics

Module-1

2 Mark Questions

1. Differentiate between active and passive components.

Passive components

Passive components are the components, they themselves are not capable of processing an electrical signal

such as amplification, oscillation, modulation etc. But these components aid the active components in

functioning. Passive components store or maintain Energy in the form of Voltage or Current. The behavior of

passive components is linear.

Examples: resistor, capacitor, inductor etc.

Active components

Active components are those, they actually processing, when signal passes through it. This process may be

amplification, modulation, frequency conversion etc. Active components produces energy in the form of

Voltage or Current. The behavior of active components is nonlinear.

Examples: transistors and diodes.

2. Write any four applications of electronics in the field of defence. Radar systems are used to detect the location of enemies. Control the aiming and firing of guns. Guided missiles are completely controlled by electronic means. Electronic circuits provide a means of secret communication between the head-quarter and

different units.

3. What is a linear resistor?

The resistors which obey Ohm’s law perfectly, are referred as linear resistors. That means a proportionate

amount of current flows through them when certain voltage is applied across them. That means current voltage

relation is linear in these resistors. In other words resistance of these resistors is constant for all applied voltages.

4. What is a non-linear resistor?

The kind of resistors where the resistance value changes with changing applied voltage and hence the current

voltage relation is not linear for these resistors means they do not obey Ohm’s law. This type of resistors is

known as non-linear resistor.

5. Which are the different types of fixed resistors?

Carbon Composition Resistors



Wire Wound Resistors

Thin Film Resistors

Thick Film Resistors

6. What is Wire Wound Resistor?

Wire wound resistors are formed by wrapping a resistive wire around a non-conducting rod. The rod was

usually made of some form of ceramic that had the desired heat properties since the wires could become quite

hot during use. End caps with leads attached were then placed over the ends of the rod making contact to the

resistive wire, usually a nickel chromium alloy.

7. What is carbon film resistor?

Carbon film resistor is made by depositing a carbon film of suitable thickness on an insulator. Pure Carbon is

generally used for this purpose. And the insulator is made of glass or ceramic.

8. What is variable resistor? Mention any two types.

When a resistor is constructed so its value can be adjusted, it is called a variable resistor. First a resistive

material is deposited on a non-conducting base. Next, stationary contacts are connected to each end of the

resistive material. Finally, a moving contact or wiper is constructed to move along the resistive material and tap

off the desired resistance.

Rheostat and potentiometer are the two types of variable resistors.

9. What is Carbon Composition Resistor?

These types of resistor are very commonly used low cost resistor. The construction of carbon composition

resistor is very simple. It is also commonly referred as carbon resistor. It is mainly made of carbon clay

composition covered with a plastic case. The lead of the resistor is made of tinned copper.

10. What are the advantages and disadvantages of Wire wound Resistors?

Wire wound resistors make lower noise than carbon composition resistors. Their performance is

well in overload conditions. They are reliable and flexible and can be used with DC and Audio

frequency range. Disadvantage of wire wound resistor is that they are costly and can’t be used in high

frequency equipments.

11. What are the applications of Wire Wound Resistors?

Wire wound resistors used where high sensitivity, accurate measurement and balanced current

control is required meter. Moreover, Wire wound resistors are generally used in high power rating

devices and equipments, Testing and measuring devices, industries, and control equipments. 12. What is the function of a fusible resistor?

A Fusible Resistor is a wire-wound resistor that is designed to burn open easily when the power rating of the

resistor is exceeded. In this way, a fusible resistor serves dual functions. When the power isn't exceeded, it



serves as a resistor limiting current. When the power rating is exceeded, it functions as a fuse, burning up, and

becoming an open in the circuit to protect components in the circuit from excess current.

13. What are tha applications of a fusible resistor?

They used widely in TV Sets, Amplifiers, and other expensive electronic circuits.

14. Which are the different types of non-linear resistors?

a).Thermisters

b).Varisters(VDR)

c). Photo Resistor or Photo Conductive Cell or LDR

15. Give the working principle and applications of a thermistor.

A thermistor is a thermally sensitive resistor whose resistance value changes with changes in operating

temperature. Thermistors exhibit either a positive temperature coefficient (PTC) or a negative temperature

coefficient (NTC). If a thermistor has a positive temperature coefficient, its resistance increases as the operating

temperature increases. Conversely, if a thermistor has a negative temperature coefficient, its resistance decreases

as the operating temperature increases.

Thermistors are used as electrical circuit components, for temperature compensation, voltage regulation, circuit protection, time delay, and volume control.

16. What is meant by a photo resistor or photo conductive cell or light dependant resistor ?

Give it’s applications.

Photoresistors are resistors whose resistance values change according to the light striking the surface of the

resistor. The material which is used to make these kinds of resistors is called photo conductors, e.g. cadmium

sulfide, lead sulfide etc.

These types of resistors are used in burglar alarm, Door Openers, Flame detectors, Smock detectors, light

meters, light activated relay control circuits, industrial, and commercial automatic street light control and

photographic devices and equipments.

17. What is the value of the electrical resistance of the resistor with colour rings as follows:

a. Yellow, grey, red, and gold

b. orange, white, brown, and gold

c. green, blue, yellow, and silver

(a) yellow = 4

grey = 7

red = 2

gold = ± 5%



write '4 'and '7', then follow these two numbers with 2 digits '0 '. The results obtained are 4700 Ω or 4.7

kΩ with a tolerance ± 5%

(b) orange = 3

white = 9

brown = 1

gold = ± 5%

Results obtained is 390 Ω with a tolerance ± 5%

(c) Green = 5

blue = 6

yellow = 4

Silver = ± 10%

Results obtained are 560,000 Ω or 560 kΩ with a tolerance ± 10%

18. What colour rings on the body of the resistor, the value of resistance mentioned below.

(a) 1K Ω ,(b) 2.2 KΩ (c) 1MΩ

(a) Brown = 1

Black = 0

Red = 102

gold = ± 5%

Results obtained is 1000 Ω or 1 kΩ

(b) red = 2

red = 2

red = 102

gold = ± 5%

Results obtained is 2200 Ω or 2.2 kΩ

(c) brown = 1

black = 0

Green = 5

colorless = ± 20%

Results obtained are 1000000 Ω or 1 MΩ with tolerance ± 20%.

19. What is the role of a capacitor in an electronic circuit?

A capacitor is a physical device which is capable of storing energy by virtue of a voltage existing across it. The

voltage applied across the capacitor sets up an electric field within it and the energy is stored in the electric field.

A capacitor is basically meant to store electrons (or electrical energy), and release them when required. A

capacitor passes AC current and blocks DC current.



15. Give the comparison between inductor and capacitor

a. Capacitors b. Inductors

c. Blocks Direct Current d. Blocks Alternating Current

e. Passes Alternating Current f. Passes Direct Current

g. Voltage in Capacitor cannot change

instantly

h. Current in an Inductor cannot change instantly

i. Quick Voltage change produces large

Current

j. Quick Current change produces large Voltage

k. Stores Energy in Electric Field l. Stores Energy in Magnetic Field

16. Discuss the construction, working and application of electrolytic capacitor.

Ans: An electrolytic capacitor is a type of capacitor that uses an electrolyte to achieve a larger

capacitance than other capacitor types. An electrolyte is a liquid or gel containing a high

concentration of ions. Almost all electrolytic capacitors are polarized, which means that the

voltage on the positive terminal must always be greater than the voltage on the negative

terminal.

An electrolytic capacitor consists of an aluminium-foil electrode which has an

aluminium-oxide film covering on one side. The aluminium plate serves as the positive plate

and the oxide as the dielectric. The oxide is in contact with a paper or gauze saturated with an

electrolyte. The electrolyte forms the second plate (negative) of the capacitor. Another layer

of aluminium without the oxide coating is also provided for making electrical contact between

one of the terminals and the electrolyte. In most cases, the negative plate is directly connected

to the metallic container of the capacitor. The container then serves as the negative terminal

for external connections.



Applications of electrolytic capacitors They are commonly used as filtering devices in various power supplies to reduce the voltage ripple. When used in switching power supplies, they are often the critical component limiting the usable life of the power supply, so high quality capacitors are used in this application. They may also be used in input and output smoothing as a low pass filter if the signal is a DC signal with a weak AC component.

17. What is an inductor?

An inductor has been defined as a physical device which is capable of storing energy by virtue of a current

flowing through it. In case of an inductor current does not change instantaneously. It offers high impedance to

ac but very low impedance to dc. It blocks ac signal but passes dc signal.

18. What are the factors Affecting Inductance?

a. The amount of inductance in an inductor is dependent on:

b. The number of turns of wire in the inductor.

c. The material of the core.

d. The shape and size of the core.

e. The shape, size and arrangement of the wire making up the coils.

19. A number 104 is written on the body of a ceramic capacitor.What is the value of capacitance?

Ans: 10,0000 pf = 100nf = o.1 µF

20. Mention the difference between core and shell type transformers.

In core type , the windings surround the core considerably and in shell type the core surround the winding.

21. Give the emf equation of a transformer and define each term.

Emf induced in primary coil E1 = 4.44 fΦ mN1 volt.

Emf induced in secondary coil E2 = 4.44fΦ mN2 volt.

Where f is the frequency of AC input Φ m is the maximum value of flux in the core N1, N2 are the number of

primary and secondary turns.

22. Distinguish between power transformer and distribution transformer.

Power transformers have very high power ratings in the order of MVA. They are used in generating and

receiving stations. Sophisticated controls are required. Voltage ranges will be very high. Distribution

transformers are used in consumer side. Voltage levels will be medium. Power ranging will be small in order of

kVA. Complicated controls are not needed.

23. What are the applications of a step-up and step-down transformers ?

Step-up transformers are used in generating stations. Normally the generated voltage will be either 11

kV . This voltage(11 KV) is stepped up to 110 kV or 220 kV or 400 kV and transmitted through

transmission lines. (In short it may Be called as sending end).



Step-down transformers are used in receiving stations. The voltage are again stepped down to 11 kV

or 22 kV and transmitted through feeders.(In short it may be called as receiving end). Further these 11

kV or 22kV are stepped down to 3 phase 400 V by means of a distribution transformer and made

available at consumer premises. The transformers used at generating stations and receiving stations

are called power transformers.

24. What is meant by an audio transformer? What are its applications?

Audio transformers are those specifically designed for use in audio circuits to carry audio signal. They can be used to block radio frequency interference or the DC component of an audio signal, to split or combine audio signals, or to provide impedance matching between high and low impedance circuits. Audio Frequency Transformers are used in audio amplifier circuits, they were essential in valve (tube) designs for matching the high impedance outputs of theses amplifiers to low impedance loudspeakers.

25. What is meant by auto transformer? What are its applications?

An autotransformer is a transformer having part of its winding included in both the input and output circuit. There is one common winding which forms both primary and secondary winding in which voltage is varied by changing the position of secondary tapping on the body of the coil.

Applications of autotransformer

Used in both Synchronous motors and induction motors. Used in electrical apparatus testing labs since the voltage can be smoothly and continuously varied.Used as boosters in AC feeders to increase the voltage levels. 26. What is meant by a pulse transformer? What are its applications?

Pulse transformer is a type of transformer designed for transmission of voltage pulses between its windings and into the load. Pulse transformers can be used for signal transmission, low-power control circuits, as well as the main components in high-power switched-mode power supplies.

27. What are the applications of distribution transformer?

Distribution transformers are widely used in various fields. Some of its common applications include:

Telecommunications Data processing equipment Transmission lines Radar systems Photocopying machines

28. What is the copper loss in a transformer?

Copper loss is the term often given to heat produced by electrical currents in the conductors of transformer windings, or other electrical devices. Copper losses is due to the resistance of the windings and is given by I2R. Loss can be minimized using thicker gauge of wire.

29. What is an electromagnetic relay?



Electromechanical relays are electrically operated switches that rely on mechanical contacts as the switch

mechanism. These are also known as armature relays. They are made of coils and contacts. When the coil is

energized, the induced magnetic field moves the armature, which opens or closes the contact.

30. What are the advantages of relay?

a. Contacts can switch AC or DC

b. Low initial cost

c. Very low contact voltage drop, thus no heat sink is required

d. High resistance to voltage transients

31. What are the applications of relay?

Relays are used to realize logic functions. They play a very important role in providing safety critical logic.

Relays are used to provide time delay functions. They are used to time the delay open and delay close of

contacts. Relays are used to control high voltage circuits with the help of low voltage signals. Similarly they are

used to control high current circuits with the help of low current signals.

They are also used as protective relays. By this function all the faults during transmission and reception can be

detected and isolated.

32. How a contactor is different from relay? Write the application of each. When a relay is used to switch a large amount of electrical power through its contacts, it is designated by a

special name: contactor. Contactors typically have multiple contacts, and those contacts are usually normally-

open, so that power to the load is shut off when the coil is de-energized. Relays are used to realize logic

functions.

Relays are also used to provide time delay functions. They are used to time the delay open and delay

close of contacts. Relays are used to control high voltage circuits with the help of low voltage signals.

Contactors are used for controlling integral horse power motors.

5Mark Questions

1. Explain different types of fixed resistors.

2. Explain the construction of carbon composition resistor.

3. Explain the working principle of a capacitor.

4. Explain the working of electrolytic capacitor.

5. Explain different types of capacitors.

6. Write short note on the effect of electronics in industry an in society.

7. Explain the construction of electromagnetic relay.

8. Explain the working Principle of a transformer:

The basic principle of a transformer is electromagnetic induction. It consists of two separate windings

placed over the laminated silicon steel core. The winding to which input ac supply is connected is

called primary winding and the winding to which load is connected is called a secondary winding.

When ac supply of voltage v1 is connected to primary winding, an alternating flux is set up in the core.

This alternating flux when links with secondary winding, an emf is induced in it and is called mutually



induced emf. Although there is no electrical connection between primary and secondary winding, but

electrical power is transferred from primary circuit to the secondary circuit through mutual flux. The

induced emf in the primary and secondary winding depends upon the rate of change of flux linkages

(i.e. N dφ/dt). The rate of change of flux (dφ/dt) is same for both primary and secondary. In case N2 >

N1 the transformer is step up and in case N2 < N1 the transformer is step down.

Module-2

2 Mark Questions

1. what are Semiconductors? Give examples?

The materials whose electrical property lies between those of conductors and insulators are known as Semiconductors. Eg: germanium, silicon.

2. What are the types of Semiconductor?

Intrinsic semiconductor 2. Extrinsic semiconductor.

3. Define a hole in a semiconductor.

When an energy is supplied to a semiconductor a valence electron is lifted to a higher energy level. The departing electron leaves a vacancy in the valence band. The vacancy is called a hole. Thus, a vacancy left in the valence band because of lifting of an electron from the valence band to conduction band is known as a hole.

4. Why is silicon preferred over germanium in the manufacture of semiconductor devices?

The silicon semiconductor devices have, in general, higher PIV and current ratings and wider temperature range than germanium semiconductor devices, that’s why silicon is preferred over germanium in the manufacture of semiconductor devices.

5. What is intrinsic semiconductor ?

An intrinsic semiconductor is one which is made of the semiconductor material in the extremely pure form (impurity content not exceeding one part in 100 million parts of semiconductors).

6. Differentiate between intrinsic semiconductors and intrinsic semiconductors?

An intrinsic semiconductor is one which is made of the semiconductor material in its extremely pure form.

When a small amount of impurity is added to a pure semiconductor crystal during the crystal growth in order to increase its conductivity, the resulting crystal is called extrinsic semiconductor.



7. Explain the term doping and its need.

The electrical conductivity of intrinsic semiconductor, which has little current conducting capability at room temperature and so is of little use, can be increased many times by adding very small amount of impurity (of the order of one atom per million atoms of pure semiconductor) to it in the process of crystallization. This process is called doping.

8. Why doping is done in semiconductors?

Intrinsic (or pure ) semiconductor by itself is of little significance as it has little current conduction capability at ordinary room temperature. However, if very small amount of impurity (of the order of one atom per million atoms of pure semiconductor) is added to it in the process of crystallization, the electrical conductivity is increased many times.

9. Describe the difference between P-type and N-type semiconductor materials.

When a small amount of trivalent impurity (such as boron, gallium, indium or aluminium) is added to a pure semiconductor crystal during crystal growth, the resulting crystal is called a P-type semiconductor.

When a small amount of pentavalent impurity (such as arsenic, antimony, bismuth or phosphrous) is added to a pure semiconductor crystal during crystal growth, the resulting crystal is called the N-type semiconductor.

10. What do you mean by donor and acceptor impurities?

Donor impurities (such as arsenic, antimony, bismuth or phosphorous) when added to a pure semiconductor lattice , form N-type extrinsic semiconductor. The pentavalent impurities are called donor impurities as such impurities donate electrons to the lattice.

Acceptor impurities (such as boron, gallium, indium or aluminium) when added to a semiconductor lattice form P-type extrinsic semiconductor. The trivalent impurities are called acceptor impurities because such impurities accept electrons from the lattice.

11. What is depletion region in PN junction?

The region around the junction from which the mobile charge carriers ( electrons and holes) are depleted is called as depletion region.since this region has immobile ions, which are electrically charged , the depletion region is also known as space charge region.

12. What is barrier potential?

Because of the oppositely charged ions present on both sides of PN junction an electric potential is established across the junction even without any external voltage source which is termed as barrier potential.

13. What is forward bias and reverse bias in a PN junction?

When positive terminal of the external supply is connected to P region and negative terminal to N region ,the PN junction is said to be forward biased. under forward biased condition the PN region offers a very low resistance and a large amount of current flows through it.

14. What is the effect of temperature on extrinsic semiconductor?

With the increase in temperature of an extrinsic semiconductor, the number of thermally generated carriers is increased resulting in increase in concentration of minority carriers. At temperature exceeding critical temperature the extrinsic semiconductor behaves like an intrinsic semiconductor but with higher conductivity.



15. Why does a pure semiconductor behave like an insulator at absolute zero temperature?

For a pure semiconductor at a temperature of absolute zero (-273.15oC)the valence band is usually full and there are may be no electron in the conduction band and it is difficult to provide additional energy required for lifting electron from valence band to conduction band by applying electric field. Hence the conductivity of a pure semiconductor at absolute zero temperature is zero and it behaves like an insulator.

16. Why silicon and germanium are the two widely used semiconductor materials?

Because the energy required to release an electron from their valence band (i.e. to break their covalent bonds ) is very small (1.12eV for Si and 0.72eV for Ge).

17. What is an ideal diode?

An ideal diode is a two terminal polarity sensitive device that has zero resistance when it is forward biased and infinite resistance when reverse biased.

18. What is break down? What are its types? When the reverse voltage across the pn junction is increased rapidly at a voltage the junction breaks down leading to a current flow across the device. This phenomenon is called as break down and the voltage is break down voltage. The types of break down are i) zener break down ii)Avalanche breakdown

19. What is zener breakdown? Zener break down takes place when both sides of the junction are very heavily doped and

Consequently the depletion layer is thin and consequently the depletion layer is tin. When a small value of reverse bias voltage is applied , a very strong electric field is set up across the thin depletion layer. This electric field is enough to break the covalent bonds. Now extremely large number of free charge carriers are produced which constitute the zener current. This process is known as zener break down.

20. What is avalanche break down? When bias is applied , thermally generated carriers which are already present in the diode

acquire sufficient energy from the applied potential to produce new carriers by removing valence electron from their bonds. These newly generated additional carriers acquire more energy from the potential and they strike the lattice and create more number of free electrons and holes. This process goes on as long as bias is increased and the number of free carriers get multiplied. This process is termed as avalanche multiplication. Thus the break down which occur in the junction resulting in heavy flow of current is termed as avalanche break down.

21. What is Reverse saturation current?

The current due to the minority carriers in reverse bias is said to be reverse saturation current. This current is independent of the value of the reverse bias voltage.

22. Differentiate between breakdown voltage and PIV of a PN diode.

The breakdown voltage of a PN diode is the reverse voltage applied to it at which the PN junction breaks down with sudden rise in reverse current. Whereas, the peak inverse voltage (PIV) is the maximum reverse voltage that can be applied to the PN junction without damage to the junction.

23. What is a zener diode?

Zener diode is a p-n junction diode specially designed for operation in the breakdown region in reverse bias condition.



24. What is zener voltage?

The voltage at which the zener diode breaks down is called the zener voltage.

25. What is a photo diode?

The photo diode is a diode in which the current sensitivity to radiation can be made much larger by the use of the reverse biased PN junction. Thus this diode conducts heavily in the reverse bias when there is some radiaton allowed to fall on the PN junction.

26. What is a LED?

A PN junction diode which emits light when forward biased is known as Light emitting diode (LED).

27. State any four advantages of LED.

They are small in size. Light in weight. Low operating temperature. Switch on time is very small. Available in different colours. They have longer life compared to lamps. Linearity is better.

28. Photodiode is a photovoltaic device or a photoconductive device or both?

Photodiode is a photovoltaic device as well as a photoconductive device. When it is operated with a reverse bias, it is photoconductive device and when operated without the reverse bias, it is a photovoltaic device.

29. What is the working principle of solar cell?

A solar cell is a p-n junction device that converts the energy of light directly into electricity (DC) using the photovoltaic effect. The process of conversion first requires a material which absorbs the solar energy (photon), and then raises an electron to a higher energy state, and then the flow of this high-energy electron to an external circuit. Silicon is one such material that uses such process.

30. Explain why an ordinary junction transistor is called bipolar? Because the transistor operation is carried out by two types of charge carriers (majority and minority carriers), an ordinary transistor is called bipolar.

31. Why transistor is called current controlled device?

The output voltage, current or power is controlled by the input current in a transistor. So it is called the current controlled device.

32. Discuss the need for biasing the transistor.

For normal operation, base-emitter junction should be forward biased and the collector-base junction reverse biased. The amount of bias required is significant for the establishment of the operating or the Q-point which is dictated by the mode of operation desired. In case the transistor is not biased properly, it would :

work inefficiently produce distortion in the output signal with the change in transistor parameters or temperature rise, the operating point may shift and

the amplifier output will be unstable.



33. Why silicon type transistors are more often used than germanium type?

Because silicon transistor has smaller cut-off current ICBO, small variations in ICBO due to variations in temperature and high operating temperature as compared to those in case of germanium type.

34. Why collector is made larger than emitter and base?

Collector is made physically larger than emitter and base because collector is to dissipate much power.

35. Define early effect.

Because of reverse bias at collector junction, the depletion layer is wide and it penetrates both in to the

base region and collector region. But the doping of the base region is much smaller than that of

collector region. Hence the penetration of the depletion layer into the base region is much greater than

the penetration into the collector region. Therefore the effective width of the base gets reduced. As the

magnitude of the reverse bias at the junction increases, the effective base width decreases. This

phenomenon is known as early effect or Base width modulation.

36. Define thermal run away.

The collector current for a CE configuration is given by : IC = β IB +ICEO.

The collector leakage current ICEO is strongly dependent on temperature. The flow of collector current

produces heat within the transistor. This raises the transistor temperature and therefore the collector

leakage current ICEO also increases. It is clear from the above equation that if ICEO increases, the

collector current IC will also increases. The increased IC will raise the temperature of the transistor,

which in turn will cause ICEO to again increase. This effect is cumulative and in a matter of seconds, the

collector current may become very large, causing the transistor to burn out. The self-destruction of

transistor is known as thermal runaway.

37. Draw a sketch to show all the current components of an NPN transistor and derive the relation between currents.

Ans:



The current that flows across the emitter-base junction is known as emitter current IE, which is the sum of electron current and hole current. The direction of IE is out of the emitter lead, which is in the direction of hole current and opposite to the direction of the electron current.However,the electron component is much larger than the hole component, the emitter current is dominated by the electron component. Thus,

퐼 = 퐼 + 퐼 푒푞(1)

A few electrons, which are unable to reach the collector-base junction, will recombine with holes, which are majority carriers in the base. It accounts for a small base current (IB) that is supplied from the base contact.

Most of the diffusing electrons will reach the boundary of the collector-base depletion region. Because the collector is more positive than base, the diffused electrons will swept across the collector-base depletion region into the collector. They will be collected to constitute the collector current(Ic).

Therefore,

퐼 = 퐼 푒푞(4)

The emitter current is the sum of the collector and the base current. Hence,

퐼 = 퐼 + 퐼 푒푞(5)

38. Give the relation between α and β.

훼 = 퐼 퐼⁄ We know that 퐼 = 퐼 + 퐼

훼 =퐼

퐼 + 퐼

Dividing numerator and denominator by 퐼 Therefore,

훼 =퐼 퐼⁄퐼퐼 + 퐼

퐼

휶 =휷

ퟏ + 휷

39. Give the comparison between three transistor configurations.

Properties Common Base Common Emitter Common Collector

Input Impedance Low Medium High

Output Impedance Very High High Low

Voltage Gain High Medium Low

Current Gain Low Medium High

Power Gain Low Very High Medium



40. Write the type number of the following: a) Low frequency low power transistor b) High frequency low power transistor c) Power transistor d) Rectifier diode. C-Low frequency low power transistor F-High frequency low power transistor BD-Series of high power transistors The most common rectifier diodes are identified by the model numbers 1N4001 through 1N4007.

41. A bipolar NPN transistor has a DC current gain, (Beta) value of 200,IC= 4mA. Calculate the base current Ib.

IB = = × = 20

42. Calculate the collector current of a transistor having β=120 when the base current measures 15μA.

Given,

We know that, C/

Therefore C×

IC = 120 ××A

IC =1.8×10-3 A= 1.8 mA

43. Which are the two main numbering systems for semiconductor diodes and transistors? One numbering or code system is used more widely in Europe and the other in the USA. The European based system is known as the Pro-electron system, sometimes also written as Pro-Electron system, and the one used more widely in North America is the JEDEC coding system.

44. What is meant by JEDEC numbering system.

These part numbers take the form: digit, letter, sequential number, [suffix]

The letter is always 'N', and the first digit is 1 for diodes, 2 for transistors, 3 for four-leaded devices,

and so forth. But 4N and 5N are reserved for opto-couplers. The sequential numbers run from 100 to

9999 and indicate the approximate time the device was first made. If present, a suffix could indicate

various things. For example, a 2N2222A is an enhanced version of a 2N2222. It has higher gain,

frequency, and voltage ratings. Always check the data sheet.

Examples: 1N914 (diode), 2N2222, 2N2222A, 2N904 (transistors).

45. What is meant by Pro-Electron numbering system.

These part numbers take the form: two letters, [letter], sequential number, [suffix]

The first letter indicates the material:



A = Ge

B = Si

C = GaAs

R = compound materials.

The second letter indicates the device type and intended application:

A: diode, RF

C: transistor, AF, small signal

D: transistor, AF, power

F: transistor, HF, small signal

L: Transistor, HF, power

U: Transistor, power, switching

Z: Zener, or voltage regulator diode

The third letter indicates if the device is intended for industrial or commercial applications. It's usually a

W, X, Y, or Z. The sequential numbers run from 100-9999.

Examples: BC108A, BAW68, BF239, BFY51.

5Mark Questions

1. Explain the V-I characteristics of a junction diode.

2. Give any four diode specifications.

3. Explain the zener diode characteristics.

4. Explain break down mechanism in a PN junction diode.

5. Explain the working principle of LED.

6. Explain the working principle of Photo diode.

7. Explain the working principle of sollar cell.

8. Explain the input characteristics of CE configuration.

9. Expalain the output characteristics of CE configuration.

10. Explain any four transistor parameters.

Module-3

2 Mark Questions

1. What is the need of filter in power supply circuit.

The output after being processed by full wave rectifier is not a pure DC. The output is a pulsating DC.

The output contains large fluctuations in voltages. The power supply that we intend to design must not

have any variation in output voltage. The voltage that we get from full wave rectifier fluctuates

between 0 V and Vpeak, and hence it contains AC components. These AC components needs to

be filtered out so as to obtain DC voltage.

2. Define rectifier. Mention the types.



Rectifier: A rectifier is a circuit that converts AC into pulsing DC. It uses unidirectional conducting

devices like PN diodes.

Rectifiers are classified into two types based on the conduction of AC input. They are: (a) Half wave

rectifier (HWR). (b) Full wave rectifier (FWR).

3. What are the advantages and disadvantages of full wave rectifier?

Advantages of Full wave rectifier

Rectifier efficiency is 81.2%.

Ripple frequency is two times the input frequency.

Ripple factor of full wave is 0.48.

Disadvantages of Full wave Rectifier

It is difficult to locate the centre tap on the secondary winding.

The diodes used have high peak inverse voltage.

4. Define ripple factor of a rectifier.

The purpose of a rectifier is to convert AC into DC. But the pulsating output of a rectifier contains a

DC component and an AC component, called ripple. The ratio of RMS value of AC components to the

DC component in the rectifier output is called ‘ripple factor’. The ripple factor is very important in

deciding the effectiveness of a rectifier. It indicates the purity of the DC power output. The smaller the

ripple factor, the lesser the effective AC component and hence more effective is the rectifier.

5. Why is the ripple of HWR higher than that of FWR?

In the half wave rectifier, the output current in the load contains, in addition to dc component,

ac components of basic frequency equal to that of the input voltage frequency. The residual ac

ripples is very low in the output of a bridge rectifier. Therefore the ripple factor is high in the

half wave rectifier than in the full wave rectifier.

6. What is the need for a filter in rectifier?

The output of a rectifier is pulsating and contains a steady DC component with undesirable ripples. If

such pulsating DC is given to the electronic circuits, it produces disturbances and other interferences.

Hence ripples have to be kept far from the load. This is achieved by use of a filter circuit in between

the rectifier and load.

7. What is PIV of a diode in a rectifier circuit? What is the importance of it?

Peak Inverse Voltage (PIV) is the maximum possible voltage that occurs across a diode when it is

reverse biased. If the applied voltage in reverse biased condition exceeds peak inverse voltage (PIV)

rating of the diode, then the diode may get damaged.

8. What is voltage regulator?



A voltage regulator is a circuit which makes the rectifier-filter output voltage constant regardless of the

variations in the input voltage or load.

9. Why is zener diode used as a voltage regulator?

Zener diode has the property of behaving like a dc battery in ‘on’ state (i.e. when the voltage across the

zener diode exceeds its zener voltage rating VZ) . In ‘on’ state , the voltage across zener diode remains

constant until the voltage across it deops less than VZ . This property of zener diode makes its use as a

voltage regulator.

10. Which are the two parameters used to measure the performance of voltage regulator?

11. OR

Define line regulation and load regulation.

Two parameters used to measure the performance of voltage regulator are line regulation and load

regulation.

Line regulation is the ratio of change in output voltage to the change in source voltage.

퐿푖푛푒푟푒푔푢푙푎푡푖표푛 =∆푉∆푉

Load regulation is defined as the ratio of change in output voltage to the change in load current.

퐿표푎푑푟푒푔푢푙푎푡푖표푛 =∆푉∆퐼

12. Explain how zener diode maintains constant voltage across the load?

Zener diode has the property of behaving like a dc battery in ‘on’ state. If the zener diode is shunted

across the load RL and the voltage across zener diode is more than the zener voltage VZ then zener

diode is on ‘on’ state , and any variation in voltage across the zener diode due to variations either in

supply voltage or in load resistance is not able to change the output voltage. Thus zener diode

maintains voltage constant across the load.

13. What are the limitations of a zener voltage regulator?

A basic zener voltage regulator has the following draw backs :

It has low efficiency for heavy load currents. It is because if the load current is large, there

will be considerable power loss in the series limiting resistance.

The output voltage slightly changes due to zener impedance as Vout = VZ + IZ ZZ. Changes in

load current produce changes in zener current. Consequently, the output voltage also changes.

Therefore, the use of this circuit is limited to only such applications where variations in load

current and input voltage are small.

14. What are the Advantages of SMPS?

High efficiency: The switching action means the series regulator element is either on or off

and therefore little energy is dissipated as heat and very high efficiency levels can be

achieved.



Compact: As a result of the high efficiency and low levels of heat dissipation, the switch

mode power supplies can be made more compact.

Flexible technology: Switch mode power supply technology can be sued to provide high

efficiency voltage conversions in voltage step up or "Boost" applications or step down "Buck"

applications.

15. Why CE configuration is most popular in amplifier circuits?

CE configuration is mainly used because its current, voltage and power gains are quite high and the

ratio of output impedance and input impedance are quite moderate.

16. What are the advantages and disadvantages of RC coupled amplifier.

Advantages of R-C Coupled Amplifier:

Excellent frequency response.

Cheaper in cost.

Very compact circuit.

Disadvantages of R-C Coupled Amplifier:

Low voltage and power gain.

Tendency of becoming noisy with age.

Poor impedence matching.

17. What is meant by operating point?

Quiescent point is a point on the dc load line which represents VCE and IC in the absence of ac signal

and variations in VCE and IC take place around this point when ac signal is applied.

18. Describe the role of different capacitors in RC coupled amplifier? Ans: The input capacitor Cin couples a.c signal voltage to base of the transistor.In the absence of Cin the signal source will be in parallel with resistor R2 and the bias will be affected.Thus the function of Cin is to allow only the alternating current from the signal source to flow in to the input circuit.The emitter bypass capacitor CE,offers low reactance path to the signal.If it is not present ,the the voltage drop across RE will reduce the effective voltage available across the base-emitter terminals (the input voltage) and thus reduces the gain.The coupling capacitor Cout transmits a.c signal but blocks the d.c voltage of the first stage from reaching the base of the second stage in the case of multistage amplifiers.

19. Discuss the role of bypass capacitor in a single stage RC coupled amplifier.

The emitter bypass capacitor CE,offers low reactance path to the signal.If it is not present ,the the

voltage drop across RE will reduce the effective voltage available across the base-emitter terminals (the

input voltage) and thus reduces the gain.

20. Define (i) feedback (ii) positive feedback and (iii) negative feedback.

Feedback: The process of combining a fraction of the output (of a Device-amplifier) back to its input

is called feedback.



Positive Feedback: If the feedback is in phase to the input, it is called positive feedback.

Negative Feedback: When the feedback is in opposition (out of phase) to the input, it is called

negative feedback.

21. What are the advantages of a negative feedback?

The advantages of negative feedback are: reduction in distortion, stability in gain, increased bandwidth

and improved input and output impedances. It is due to these advantages that negative feedback is

frequently employed in amplifiers.

22. What is meant by oscillator?

An oscillator is a circuit which produces an output signal without providing any input signal.

22. Write down the general applications of oscillators.

a) As a local oscillator in radio receivers.

b) In T.V receivers.

c) In signal generators.

d) As clock generation for logic circuits.

e) AM and FM transmitters. 23. What is Barkhausen criterion?

An amplifier with positive feedback results in oscillations if the following conditions are satisfied:

o The loop gain ( product of the gain of the amplifier and the gain of the feedback network) is

unity.

i.e, Aβ = 1

o The total phase shift in the loop is 00.

This is known as the Barkhausen criterion for oscillation.

24. What are the essential parts of an Oscillator?

Tank circuit (or) Oscillatory circuit. b) Amplifier (Transistor amplifier) c) Feedback Circuit.

25. List the advantages and applications of RC phase shift Oscillator.

Advantages

It is best suited for generating fixed frequency signals in the audio frequency range.

Simple Circuit.

Pure sine wave output is possible.

Applications

RC phase shift oscillators are used for musical instruments, oscillators, voice synthesis, and

GPS units. They work at all audio frequencies. 26. Why RC phase shift is needed in a RC phase shift Oscillator?

The amplifier used causes a phase shift of 180o than the feedback network should create phase shift of

180o , to satisfy the Barkhausen Criterion. Hence in a phase shift oscillators, three sections of RC

circuit are connected in cascade, each introducing a shift of 60o , thus introducing a total phase shift of

180o , due to feedback network.

5Mark Questions



1. Draw and explain the block diagram of regulated power supply.

2. With neat diagrams,explain the working of half wave rectifier.

3. With a neat single circuit diagram and waveforms, explain the working of a full wave bridge rectifier

with a capacitor filter.

4. Explain how zener diode is used as a voltage regulator.

5. Draw and explain the block diagram of SMPS.

6. With neat circuit diagram,explain the working of RC coupled amplifier.

7. Explain the frequency response of RC coupled amplifier.

8. Explain public address system.

9. Explain the working principle of oscillator.

10. Explain the working of RC phase shift oscillator.

Module-4

2 Mark Questions

1. What is an IC?

An integrated circuit (IC) is a miniaturised electronic circuit in which all active and passive

components such as transistor, diodes, resistors, capacitors etc. are fabricated on the surface of a

semiconductor substrate.

2. What are the advantages of ICs over discrete component circuits?

The advantages of IC’s over discrete component circuits are extremely small size, very small weight,

very low cost, lower power consumption, more reliability, easy replacement, increased operating speed,

close matching, improved functional performance, suitability for small signal operation etc.

3. Differentiate between analog and digital integrated circuits. Write at any two application specific integrated circuits from each group.

Ans:

In analog ICs, the input and output signals are continuous. The output signal level depends upon

the input signal level and the output signal level is a linear function of input signal level. Linear

ICs or analog ICs are most commonly used as audio frequency amplifier and radio frequency

amplifier. Op amps, voltage regulators, comparators and timers are also well-known examples of

linear ICs or analog ICs.

Examples for analog ICs

IC741 - operational amplifier and

NE 555 – timer IC



The digital ICs operate with binary data such as either 0 or 1. Normally in digital circuit, 0

indicates 0 V and one indicate +5 V. The logic Gates, such as AND gate, OR gate, NAND gate,

XOR gate, flip flops, counters; microprocessors are some well-known examples of digital ICs.

Examples for analog ICs

IC 7400 – NAND gate operation

IC 7402 – NOR gate operation

4. What is monolithic IC?

A monolithic IC is one in which all circuit components and their interconnections are formed on a

single thin wafer, called the substrate.

5. What are the basic logic elements?

Basic logic elements are NOT gate, AND gate, OR gate and the flip-flop.

6. What is a truth table?

Truth table is a table that gives outputs for all possible combinations of inputs to a logic circuit.

7. What are the universal logic gates?

Universal gate is a gate that can perform all the basic logical operations such as NAND and NOR gates.

8. Draw the symbols and truth tables of NAND gate and NOR gate.

NAND Gate



NOR Gate

9. What is an operational amplifier?

An operational amplifier is a high gain, direct-coupled amplifier consisting of one or more differential

amplifier stages.It can be use to perform different mathematical operations like addition,substraction

etc.

10. What are the ideal characteristics of an operational amplifier?

Infinite open-loop gain

Infinite input impedance

Zero output impedance

Infinite frequency bandwidth

Infinite slew rate

Infinite common-mode rejection ratio

11. Define CMRR.

CMRR is defined as the ration of differential voltage gain to common-mode voltage gain and it is given

as CMRR = Ad/Acm

12. Define slew rate.

Slew rate of an op-amp is defined as the maximum rate of change of output voltage per unit time and is

expresses in V/µs.

13. What is an inverting amplifier?

In an inverting amplifier, the input is connected to the minus or inverting terminal of op-amp.

14. What is a comparator?



A comparator is a circuit which compares a signal voltage applied at one input of an op-amp with a

known reference voltage at the other input. It is an open loop op - amp with output + Vsat .

15. What are the applications of comparator?

Zero crossing detector

Window detector

Time marker generator

Phase detector

16. What is a multimeter?

A multimeter is an electronic instrument which can measure resistances, currents and voltages. It is an

indispensable instrument and can be used for measuring d.c. as well as a.c. voltages and currents. Multimeter is

the most inexpensive equipment and can make various electrical measurements with reasonable accuracy.

17. What are the advantages of digital multimeter?

They are more accurate than analog multimeters.

They reduce reading and interpolation errors.

Digital multimeter displays have no moving parts. This makes them free from wear and shock failures.

Digital output is suitable for further processing or recording .

DMMs can be used in testing continuity, capacitors, diodes and transistors. More advanced digital

multimeters can also measure frequency.

18. What is the principle of DSO?

The DSO converts the signals into a digital format using an analogue to digital converter (ADC), then it stores

the digital data in the memory, and then processes the signals digitally, finally it converts the resulting signal in

a picture format to be displayed on the screen of the scope. Since the waveform is stored in a digital format, the

data can be processed either within the oscilloscope itself, or even by a PC connected to it. One advantage of

using the DSO is that the stored data can be used to visualize or process the signal at any time. The analogue

scopes do not have memory therefore the signal can be displayed only instantaneously.

19. What is a function generator?

A function generator is a signal source that has the capability of producing different types of waveforms as its

output signal. The most common output waveforms are sine-waves, triangular waves, square waves, and saw

tooth waves. The frequencies of such waveforms may be adjusted from a fraction of a hertz to several hundred

kHz.

5 Mark Questions

1. Draw and explain the block diagram showing the various circuit units in an operational

amplifier.



2. Draw a non-inverting operational amplifier circuit and derive the expression for its voltage

gain. 3. Draw an inverting operational amplifier circuit and design it for a voltage gain of 10.

The source Vs in series with a resistance R1 is at inverting input terminal of the op-amp.another resistor Rf is connected across the output and the inverting input terminal.This circuit connection provides a negative feedback because any increase in output signal results in a feedback signal into the inverting input,causing a decrerase in the output signal.The non-inverting terminal is connected to ground.The point D is at virtual ground ie.,Id=0 and Vd=0.

Equilent Circuit:

Thus the voltage gain of inverting amplifier is given by

Given Av = 10, Choose R1 = 10 K Av = -Rf/R1 , Therefore Rf = 10 × 10K = 100 K

4. Explain comparator circuit.

5. Draw the symbol and truth table of OR gate and NAND gate.

6. With a block diagram, explain the working of a digital multimeter.

7. Draw and explain the block diagram of DSO.

8. Draw and explain the block diagram of function generator.



Module-5

2 Mark Questions

1. Define amplitude Modulation.

Amplitude Modulation is the process of changing the amplitude of a high frequency carrier signal in

proportion with the instantaneous value of the modulating signal.

2. Define Modulation index and percent modulation for an AM wave.

Modulation index is a term used to describe the amount of amplitude change present in an AM

waveform .It is the ratio of amplitude of the modulating signal to the amplitude of the carrier signal.

m = Em/Ec

3. What is the importance of modulation index?

The modulation index (or modulation depth) of a modulation scheme describes by how much the

modulated variable of the carrier signal varies around its unmodulated level.

4. Define Heterodyning.

Heterodyne means to mix two signals of different frequencies in a nonlinear device and to produce a

signal of new frequency.

5. What is frequency modulation? Write the frequency bands used for AM and FM broadcast.

Frequency modulation is the process of varying the frequency of the carrier in accordance

with the instantaneous amplitude of the modulating signal.

AM radio ranges from 535 to 1705 KHz (OR) Up to 1200 bits per second.

FM radio ranges in a higher spectrum from 88 to 108 MHz.

6. Define frequency deviation.

Frequency deviation is the change in frequency that occurs in the carrier when it is acted on by a

modulating signal frequency.

7. Give the comparison between AM and FM.

A.M F.M

A.M is used in wide range of frequencies. Range of F.M is restricted.

Narrow bandwidth is required. Large bandwidth is required.

The equipment required for A.M transmission

is less costly.

The equipment required is complex and also

expensive.

Most of power in A.M is in the carrier which

does not carry any information.

All the power transmitted is useful in the F.M

system.



Signal to noise ratio is poor in A.M. Signal to noise ratio is more in F.M.

Interferences are more. Interferences are less.

7. What are the differences between AM Receiver and FM receiver:

The operating frequency of FM receiver is high.i.e,88MHz to 108 MHz.

The intermediate frequency of FM is high.ie.,10.7 MHz.

A limiter circuit is required in FM receivers,whereas no such arrangment is required in AM receiver.

The de-emphasis circuit is required for FM receiver.

The FM receiver circuit is more complicated than AM receiver.

8. Write short notes on different frequency bands used for communication.

The allocation of frequency for satellite communication is a complicated process. This requires

international co-ordination and planning and this is carried out under the auspices of the International

Telecommunication Union (ITU). The allocation of frequency shall be carried out depending upon the

type of service provided by the satellite, for example, Broad casting satellite service is providing land

and aeronautical communication. The ITU has decided the frequency bands for various type of

communication. The band designation, their nominal frequency range and principle use is given in

table.

Band Designation Nominal Freq: Range Principal Uses: HF 3-30 MHz Short-Wave Broad cast

VHF 30-300 MHz FM,TV UHF 300-3000 MHz TV,LAN,Cellular ,GPS

L 1-2 GHz Radar,GSO Satellite S 2-4 GHz -do- C 4-8 GHz Satellite Data Links X 8-12 GHz -do-

Ku 12-18 GHz Radar,Satellite Data Links K 28-27 GHz -do-

Ka 27-40 GHz Radar,Automotive Data mm(millimeter Wave) 40-300 GHz

9. What is a radar?

Radar is an acronym for ‘radio detection and ranging’. Radar is an electromagnetic system for the

detection and location of reflecting objects such as aircraft, ships, spacecraft, vehicles, people, and the

natural environment. It operates by radiating energy into space and detecing the echo signal reflected

from an object or target.

10. What are the applications of radar? ƒ

Military

Remote sensing

Air traffic control (ATC)

Law enforcement and highway safety



Aircraft safety and Navigation

Ship safety

11. What is Satellite?

An artificial body that is projected from earth to orbit either earth (or) another body of solar systems.

Types: Information satellites and Communication Satellites .

12. Define Satellite Communication.

It is defined as the use of orbiting satellites to receive, amplify and retransmit data to earth stations.

13. Which are the different classification of Satellites:

Satellites are generally classified as having a low earth orbit (LEO), medium earth orbit (MEO), or

Geosynchronous earth orbit (GEO).

Most LEO satellites operate in the 1GHz to 2.5 GHz frequency range. The main advantage of LEO

satellites is that the path loss between earth stations and space vehicles is much lower than for satellites

revolving in medium or high altitude orbits. Less path loss equates to low transmit powers, smaller

antennas and less weight.

MEO satellites operate in the 1.2 GHz to 1.66 GHz frequency band and orbit between 6000 miles and

12,000 miles above earth.

Geosynchronous satellites are high altitude earth orbit satellites operating primarily in the 2 GHz to

18GHz frequency spectrum with orbits 22,300 miles above earth’s surface. Most commercial

communication satellites are geosynchronous orbit.

14. What are the geostationary orbit satellites?

The satellites present in the geostationary orbit are called geostationary satellite. The geostationary

orbit is one in which the satellite appears stationary relative to the earth. It lies in equatorial plane and

inclination is ‘0’. The satellite must orbit the earth in the same direction as the earth spin. The orbit is

circular.

15. What are the features of geostationary satellite?

The orbit is circular

The orbit is in equatorial plane i.e. directly above the equator and thus inclination is zero.

The angular velocity of the satellite is equal to angular velocity of earth Period of revolution is

equal to period of rotation of earth.

Finish one revolution around the earth in exactly one day i.e. 23 hours, 56 Minutes and 4.1

seconds

16. What are the advantages of geostationary orbit satellites?

Most communications satellites in use today for commercial purposes are placed in the geostationary

orbit, because one satellite can cover almost 1/3 of Earth’s surface, offering a reach far more extensive

than what any terrestrial network can achieve.

The geosynchronous satellites remain stationary over the same orbital location, users can point their

satellite dishes in the right direction, without costly tracking activities, making communications reliable

and secure



GEO satellites are proven, reliable and secure – with a lifespan of 10-15 years.

GEO systems have significantly greater available bandwidth than the Low Earth Orbit -LEO and

Medium Earth Orbit -MEO systems. This permits them to provide two-way data, voice and broadband

services that may be unpractical for other types of systems.

Because of their capacity and configuration, GEOs are often more cost-effective for carrying high-

volume traffic, especially over long-term contract arrangements. For example, excess capacity on GEO

systems often is reserved in the form of leased circuits for use as a backup to other communications

methods.

17. What are the disadvantages of geostationary orbit satellites?

Long path length, and hence losses when compared to LEO, or MEO.

Satellites more costly to install in GEO in view of greater altitude.

Long path length introduces delays.

18. Give the two segments of basic satellite communication.

Earth segment (or) ground segment

Space segment

19. What is meant by transponder?

In a communication satellite, the equipment which provides the connecting link between the satellite’s

transmit and receive antennas is referred to as the transponder.

20. Define earth segment.

Earth segment of a satellite communication system consists of transmit earth station and receive earth

station.

21. Explain the advantage of GPS over conventional navigation.

Global coverage and assessment

More precise

High integrity and portable simple system

Augments the accuracy of the self contained systems.

5-Mark Questions

1. Why modulation is necessary in an Electronic Communication?

2. With neat waveform sketches,explain AM?Derive expression for an FM wave.

3. With neat waveform sketches,explain FM?Derive expression for an FM wave.

4. With a neat block diagram, describe the working and functions of each block of a super heterodyne

AM radio receiver.

5. With a neat block diagram, describe the working and functions of each block of a super heterodyne FM

radio receiver.

6. What are the advantages of satellite communication.

7. What is a transponder? Explain its working.

8. Explain the various communication frequency bands.



9. Draw and explain the block diagram of pulsed radar system.

10. Explain the working of GPS.

Module-6

2 Mark Questions

1. Give the advantages of mobile communication.

The term mobile communication describes any wireless communication link between two terminals, two

stations or persons of which one or both are in motion. The communication is possible from mobile to mobile or

mobile to fixed or fixed to mobile stations. Very large area of earth is visible from satellite (about 42%) i.e.

communication is possible beyond earth curvature (beyond line of sight).Mobile communication offers

communication with remote communities in sparsely populated area, which are difficult to access by other

means of communication.Mobile communication ignores political boundaries as well as geographical

boundaries.

2. Define a cell.

In mobile communication, the coverage area is divided into smaller areas which are each served by it’s

own base station. These smaller areas are called cells.

3. What is frequency reuse?

Spatially reusing the available spectrum so that the same spectrum can support multiple users separated

by a distance is called frequency reuse.

4. What is hand off?

One of the important features of a cellular system is its ability to transfer calls that are already in

progress from one cell-site controller to another as the mobile unit moves from cell to cell within the

cellular network. The base station transfer includes converting the call to an available channel within

the new cell’s allocated frequency subset. The transfer of a mobile unit from one base station’s control

to another base station’s control is called a Handoff (or Handover).

5. What are the channels used in mobile communication systems?

Forward voice channels (FVC)

Reverse voice channels (RVC)

Forward control channels (FCC)

Reverse Control channels (RCC)

6. What are the basic units of a Cellular system?

Mobile stations

Base stations

Mobile Switching Center (MSC) or Mobile Telephone Switching Office (MTSO).

7. Mention the function of the base station.

The base station serves as a bridge between all mobile users in the cell and connects the simultaneous

mobile calls via telephone lines or microwave links to the mobile switching center(MSC).

8. Define MSC and What are the functions of MSC?



MSC stands for Mobile services switching center (MSC).The MSC performs the telephony switching

functions of the system. It controls calls to and from other telephone and data systems. It also performs

such functions as toll ticketing, network interfacing, common channel signaling, and others.The MSC

coordinates the activities of all the base stations and connects the entire cellular system to the PSTN.

9. What is GSM?

GSM (Global System for Mobile communications: originally from Groupe Spécial Mobile) is the most

popular standard for mobile phones in the world. GSM differs from its predecessors in that both

signaling and speech channels are digital, and thus is considered a second generation (2G) mobile

phone system. This has also meant that data communication was easy to build into the system.

10. What are the different features of GSM?

Short message service (SMS), which is a bidirectional service for sending alphanumeric message

up to 160 bytes in length.

Subscriber identity module (SIM), which is a memory device that stores information such as

subscriber’s identification number, the networks and countries where the subscriber is entitled to

service, privacy keys, and other user specific information.

On-the-air privacy which is provided by the system. The privacy is made possible by encrypting

the digital bit stream sent by a GSM transmitter.

11. List the databases of NSS in GSM?

Home location register

Visitor location register

Authentication center

12. What are the services offered by the GSM?

There are three user services offered by GSM, they are

Bearer or data service

Telephone service

Supplementary ISDN service

13. What is optical fiber?

Optical fiber uses light instead of electricity to carry a signal. It is unique because it can carry high

bandwidth signals over long distances without degradation. Copper can also carry high bandwidth, but

only for a few hundred yards – after which the signal begins to degrade and bandwidth narrows.

14. What is the necessity of cladding for an optical fiber?

To provide proper light guidance inside the core

To avoid leakage of light from the fiber

To avoid mechanical strength for the fiber

To protect the core from scratches and other mechanical damages.

15. What are the uses of optical fibers?

To transmit the information which are in the form of coded signals of the telephone

communication, computer data, etc.

To transmit the optical images (Example : Endoscopy)

To act as a light source at the inaccessible places.



To act as sensors to do mechanical, electrical and magnetic measurements.

16. Define a fiber optic system.

An optical communications system is an electronic communication system that uses light as the carrier

of information. Optical fiber communication systems use glass or plastic fibers to contain light waves

and guide them in a manner similar to the way electromagnetic waves are guided through a waveguide.

17. What are the advantages of Optical Communication System

Optical communication systems have many advantages over copper wire-based communication

systems. These advantages include:

• Enormous potential bandwidth

• Small size and weight

• Electrical Isolation

• Signal security

• Low transmission loss

18. What are the disadvantage of Optical Fiber Communication

It requires a higher initial cost in installation

Although the fiber cost is low, the connector and interfacing between the fiber optic costs a lot.

Fiber optic requires specialized and sophisticated tools for maintenance and repairing.

19. Define refractive index.

The refractive index is defined as the as the ratio of the velocity of propagation of light ray in free

space to the velocity of propagation of a light ray in a given material.

Mathematically, the refractive index is n = c/υ where c = speed of light in free space υ = speed of light

in a given material

20. Define critical angle.

Critical angle is defined as the minimum angle of incidence at which a light ray may strike the interface

of two media and result in an angle of refraction of 90°or greater.

21. Explain the total internal reflection in optical fiber with the help of a diagram.

When the angle of incidence of the light ray is greater than the critical angle then no

refraction takes place. Instead, all the light is reflected back into the denser material. This is

called total internal reflection.



22. What are the conditions fro total internal reflection?

Light should travel from denser medium to rarer medium.

The angle of incidence should be greater than the critical angle of the denser medium.

23. Define numerical aperture.

Numerical aperture is mathematically defined as the sine of the maximum angle a light ray entering the

fiber can have in respect to the axis of the fiber and still propagate down the cable by internal

reflection.

24. what are step index and graded index fibers?

In the case of graded index fiber, the refractive index of a core is a constant and is larger than the

refractive index of the cladding. The light propagation is mainly by meridional rays.

In the case of graded index fiber (GRIN fiber) the refractive index of the core varies parabolically from

the centre of the core having maximum refractive index to the core-cladding interface having constant

minimum refractive index. Here the light propagation is by skew rays.

25. What are meridional rays?

Meridional rays are the rays following Zig Zag path when they travel through fiber and for every

reflection it will cross the fiber axis.

26. What are skew rays?

Skew rays are the rays following the helical path around the fiber axis when they travel through the

fiber and they would not cross the fiber axis at any time.

27. Define acceptance angle.

The maximum angle with which a ray of light can enter through the entrance end of the fiber and still

be totally internally reflected is called acceptance angle of the fiber.

28. Why do we prefer step index single mode fiber for long distance communication?

Step index single mode fiber has a)low attenuation due to smaller core diameter b) higher bandwidth

and c) very low dispersion.

29. What are the advantages of optical communication?

Low transmission loss.

Small size and weight.

No electromagnetic interference.

Electrical isolation.

30. Define aspect ratio?

Aspect ratio can be defined as the ratio of width to height of the picture frame. For television, it is

standardized as 4:3.

31. Why is scanning necessary in television system?

Scanning is the important process carried out in a television system inorder to obtain continuous frames

and provides motion of picture. The scene is scanned both in the horizontal and vertical directions



simultaneously in a rapid rate. As a result sufficient number of complete picture of frames per second is

obtained to give the illusion of continuous motion.

32. What do you understand by flicker?

The result of 24 pictures per second in motion pictures and that of scanning 25 frames per second in

television pictures is enough to make an illusion of continuity. But, they are not rapid enough to permit

the brightness of one picture or frame to blend smoothly in the next through the time when the screen is

blanked between successive frames. This develops in a definite flicker of light that is very irritating to

the observer when the screen is made alternately bright and dark.

33. How will you solve the flickering problem?

The flickering problem is solved in motion pictures by showing each picture twice. Hence 48 views of

the scene are shown per second although they are still the same 24 pictures frames per second. As a

result of the increased blanking rate, flicker is removed. In TV, Interlaced scaning is used to avoid

flicker.

34. What do you mean by interlaced scanning?

When the scanning beam reaches the bottom o f the picture frame, it quickly returns to the top to scan

those lines that were missed in the previous scanning. Hence the total number of lines are divided into

two groups called fields. Each field is scanned alternately. This way of scanning is called interlaced

scanning.

35. Write short notes on CATV.

CATV stands for community antenna television systems. The CATV system is a cable system

distributes good quality television signal to a very large number of receivers throughout an entire

community. Generally this system gives increased TV programmes to subscribers who pay a fee for

this service. A cable system may have many more active VHF and UHF channels than a receiver tuner

can directly select.

36. What do you understand by satellite TV?

Satellite TV is a TV from space. Broadcasters from earth transmit their programmes to specified

satellites. Then, the transmissions are returned to receiving equipment on the ground. Therefore, the

better the receiving equipment ,the higher the quality of the reception.

37. What are the applications of CCTV?

There are numerous applications of CCTV and a few are briefly described here.



Education. One instructor may lecture to a large number of students sitting at different locations.

Similarly close-ups of demonstration experiments and other aids can be shown on monitors during

these lectures.

Medicine. Several monitors and camera units can be installed to observe seriously ill patients in

intensive care units. In medical institutions, operations when performed can be shown to medical

students without their actually gathering around the operation table.

Business. Television cameras can be installed at different locations in big departmental stores to keep

an eye over customers and sales personnel.

Surveillance. In banks, railway yards ports, traffic points and several other similar locations, closed

circuit TV can be effectively used for surveillance.

38. What is the working principle of DTH?

Direct to Home is a term used to refer to satellite television broadcasts intended for home reception,

also referred to more broadly as Direct broadcast satellite (DBS) signals. The Direct-To-Home

(DTH) service is a digital satellite service that provides television services direct to subscribers

anywhere in the country. Since it makes use of wireless technology, programs are sent to the

subscriber's television direct from the satellite, eliminating the need for cables and any cable

infrastructure. DTH services also provide the finest of picture and sound quality.

39. What are the main components of DTH?

There are five major components involved in a direct to home (DTH) satellite system: the

programming source, the broadcast centre, the satellite, the satellite dish and the receiver.

40. What are the Advantages of DTH?

Availability of satellite broadcast in rural and semi-urban areas where cable is difficult to

install.

Due to digital compression techniques, many more channels are available than can be

provided by cable operators.

DTH also offers digital quality signals which do not degrade the picture or sound quality.

The DTH system can also provide many value-added services such as the Internet, e-mail,e-

commerce, and interactive multimedia.

41. What is the difference between conventional analog TV and HDTV?

One major difference between conventional analog TV and HDTV is that HDTV can use progressive

line scanning rather than interlaced scanning. In progressive scanning each line is scanned one at a

time from top to bottom. Since this format is compatible with computer video monitors, it is possible to

display HDTV on computer screens. Interlaced scanning can be used on one of the HDTV formats. In

interlaced scanning,the total number of lines are divided into two groups called fields. Each field is



scanned alternately. This way of scanning is called interlaced scanning. Interlaced scanning minimizes

flicker but complicates the video compression process. Progressive scanning is preferred and at a 50-

Hz frame rate, flicker is not a problem.

42. What is the basic principle of HDTV?

HDTV uses the scanning concept to paint a picture on the CRT, so you can continue to think of the

HDTV screen in terms of scan lines, as you would think of the standard NTSC analog screen.

However, you should also view the HDTV screen as being made up of thousands of tiny dots of light,

called pixels. Each pixel can be any of 256 colors. These pixels can be used to create any image. The

greater the number of pixels on the screen, the greater the resolution and the finer the detail that can be

represented. Each horizontal scan line is divided into hundreds of pixels. The format of a HDTV screen

is described in terms of the numbers of pixels per horizontal line by the number of vertical pixels

(which is the same as the number of horizontal scan lines).

43. List some merits of high definition television (HDTV).

Improvement in both vertical and horizontal resolution of the reproduced picyure by

approximately 2:1 over existing standards.

Much improved colour rendition.

Higher aspect ratio of atleast 5:3.

Stereophonic sound.

44. What is the working principle of Plasma TV?

Plasma TVs are basically an array of light emitting gas cells sandwiched between two glass sheets. The

fact that they do not rely on an external light source to power the display, they can give amazing true

black effect. However, a glass panel is a mandate for a plasma TV and that’s the reason they are fairly

bulky and give high glare when viewed in daylight. Each cell emitting light acts as an individual

fluorescent tube making the TV less power efficient, but the images are crisper and more natural when

compared to an LCD TV.

45. What are the characteristics of plasma display?

Ans:

Characteristics of Plasma TV

1. Plasma displays can be made upto large sizes like 150 inches diognal.

2. Very low-luminance “dark-room” black level.

3. Very high contrast.

4. The plasma display panel has a thickness of about 2.5 inches, which makes the total thickness

not more than 4 inches.



5. Has a life-time of almost 100,000 hours. After this period, the brightness of the TV reduces to

half. 46. What are the advantages and disadvantages of Plasma TV ?

Advantage

Produce excellent natural black.

Amazing picture quality and screen refresh rate. Ideal for gaming.

Disadvantage

Bulky and less energy efficient.

The screen glares when used in day light.

47. What is the working principle of LCD TV?

In an LCD TV, an LCD screen is at the front of a fluorescent backlight display. The television displays

the image when the light from behind the screen falls on the LCD screen and a picture is built up with

the combinations of the colors.

48. What are the advantages and disadvantages of LCD TV ?

Advantages

The LCD TVs are relatively inexpensive and is the best bet for anyone looking for a flat screen

television.

Disadvantages

One of the biggest disadvantages of the LCD display is that it cannot give a true black color

experience.

Not suitable for high frame rate gaming due to motion delays and higher latency.

49. What is the working principle of LED TV?

LED (Light Emitting Diodes) TVs are basically LCDs only. The difference is that the lamp behind the

screen that was used to illuminate the fluorescent display in LCD is replaced by small LEDs. The

working of the TV remains the same, but due to the use of LEDs the screen is much slimmer in

size, power efficient and can yield a true black effect to a much greater extent.

50. What are the advantages and disadvantages of LED TV ?

Advantages

LED TVs are incredibly slim when compared to the other kinds and come in variety of sizes.

Due to the use of smaller LEDs to illuminate the display they consume less power.

They have high response time and thus one can enjoy high frame console gaming without any

motion delay and lags.

Provide a richer, true black experience experience than the LCD TVs.

LED television has a wider viewing angle around 175 degrees, which gives a better picture

quality even when you are viewing it from the corners.

Disadvantage

They are expensive when compared to LCDs and Plasma TVs.



5Mark Questions

1. Draw and explain the architecture of GSM.

2. What is the importance of total internal reflection in fiber optic communication?

Total internal reflection is a phenomenon that happens when a propagating wave strikes

a medium boundary at an angle larger than a particular critical angle with respect to the normal to the

surface . If the refractive index is lower on the other side of the boundary and the incident angle is

greater than the critical angle, the wave cannot pass through and is entirely reflected. The critical angle

is the angle of incidence above which the total internal reflectance occurs.

Total internal reflection is a powerful tool since it can be used to confine light. One of the most

common applications of total internal reflection is in fibre optics. An optical fibre is a thin, transparent

fibre, usually made of glass or plastic, for transmitting light.

The basic functional structure of an optical fiber consists of an outer protective cladding and an inner

core through which light pulses travel. The difference in refractive index of the cladding and the core

allows total internal reflection in the same way as happens.

If light is incident on a cable end with an angle of incidence greater than the critical angle then the

light will remain trapped inside the glass strand. In this way, light travels very quickly down

the length of the cable over a very long distance (tens of kilometers).

3. Explain the working principle of plasma TV.

4. Explain the working principle of HDTV.

5. Explain the working of CATV.

6. Explain the working of CCTV.

7. Draw and explain the block diagram of a fiber optic communication system.

8. Explain the different components and their functions of the DTH system.

bel model questions & answers - infonics · 2016. 2. 26. · ec100: basics of electronics...

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