ELECTRONICS AND COMMUNICATION PAGE 1
Contributed by Mercy Benyl
1) Define engineering
The application of science to the needs of humanity and a profession in which a knowledge of the mathematical and natural sciences gained by study, experience, and practice is applied with judgment to develop ways to use economically the materials and forces of nature for the benefit of mankind.
2) Define Electronic
The study and use of electrical devices that operate by controlling the flow of electrons or other electrically charged particles.
3) Define Communication
Communication means transferring a signal from the transmitter which passes through a medium then the output is obtained at the receiver (or) The transferring of message from one place to another place is called as communication.
4) What is interbase resistance of UJT?
The resistance between the two bases (B1and B2) of UJT is called as interbase resistance.
Interbase resistance = RB1 + RB2
RB1- resistance of silicon bar between B1 and emitter junction.
RB2 - resistance of silicon bar between B2 and emitter junction
5) Give the expression for peak point voltage for UJT?
VP = ή . VBB + VD
Where VP - peak point voltage, ή - intrinsic stand -off ratio, VBB - voltage applied between the bases and VD – barrier potential of UJT
6) How does a mobile work?
When you talk into a mobile telephone it converts the sound of your voice to radiofrequency energy (radio waves). The radio waves are transmitted through the air to a nearby base station. The base station then sends the call through the telephone network until it reaches the person you are calling. When you receive a call on your mobile phone the message travels through the telephone network until it reaches a base station near to you. The base station sends out radio waves, which are detected by your telephone and converted back to speech. Depending on the equipment and the operator, the frequency that each operator utilises is 900MHz, 1800MHz or 2100MHz. The mobile phone network operates on the basis of a series of cells. Each cell requires a radio base station to enable it to function. There are three types of base station and each has a particular purpose: 1. The Macrocell is the largest type and provides the main coverage for mobile phone networks. 2. The Microcell is used to improve capacity in areas where demand to make calls is high, such as shopping centres. 3. The Picocell only has a range of a few hundred metres and may be used to boost weak signals within large buildings. Each base station can only cope with a certain number of calls at any one time. So if demand exceeds the capacity of a base station an additional base station is needed.
7) What is a SCR?
A silicon controller rectifier (SCR) is a three terminal, three junction semiconductor device that acts as a true electronic switch. It is a unidirectional device. It converts alternating current into direct current and controls the amount of power fed to the load.
8) Define break over voltage of SCR.
Break over voltage is defined as the minimum forward voltage with gate open at which the SCR starts conducting heavily.
9) Why SCR cannot be used as a bidirectional switch?
SCR can do conduction only when anode is positive with respect to cathode with proper gate current. Therefore, SCR operates only in one direction and cannot be used as bidirectional switch.
10) Define demodulation-
Demodulation is the act of removing the modulation from an analog signal to get the original baseband signal back. Demodulating is necessary because the receiver system receives a modulated signal with specific characteristics and it needs to turn it to base-band.
11) What do you mean by ASCII, EBCDIC?
ASCII (American Standard Code for Information Interchange), is a character encoding based on the English alphabet. EBCDIC (Extended Binary Coded Decimal Interchange Code) is an 8-bit character encoding used on IBM mainframe operating systems
12) What do you mean by 3 dB cutoff frequency? Why is it 3 dB, not 1 dB?
3db implies 70%(o.7o7) of the power, i'e we r interested to consider the bandwidth range from peak to 70% because upto 70% its reliable. Hence 3db is called as half power freq. 3db value is the mean square value which is 70% of the maximum value.
13) What is a Ohmic contact?
An ohmic contact is a low resistance junction providing conduction in both direction between metal and the semiconductor. Ohmic contact acts as contact between any semiconductor device and outside world.
14) Give the types of ohmic contact.
(a). Non rectifying barrier (b). Tunneling barrier
15) What does UJT stands for? Justify the name UJT.
UJT stands for unijunction transistor. The UJT is a three terminal semiconductor device having two doped regions. It has one emitter terminal (E) and two base terminals (B1and B2). It has only one junction, moreover from the out look, it resembles to a transistor hence the name unijunction transistor.
16) What is a repeater?
A repeater is an electronic device that receives a signal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances without degradation.
17) What is attenuation? Attenuation is the reduction in amplitude and intensity of a signal. Signals may attenuate exponentially by transmission through a medium, or by increments calculated in electronic circuitry or set by variable controls. Attenuation is an important property in telecommunications and ultrasound applications because of its importance in determining signal strength as a function of distance. Attenuation is usually measured in units of decibels per unit length of medium (dB/cm, dB/km, etc) and is represented by the attenuation coefficient of the medium in question.
18) How do microwave oven works?
Heart of microwave oven is magnatron which generates frequency of appox. 2.4 GHz.
19) Define holding current in a SCR.
Holding current is defined as the minimum value of anode current to keep the SCR ON.
20) List the advantages of SCR.
(a). SCR can handle and control large currents.
(b). Its switching speed is very high
(c). It has no moving parts, therefore it gives noiseless operation.
(d). Its operating efficiency is high.
21) List the application of SCR.
a. It can be used as a speed controller in DC and AC motors.
b. It can be used as an inverter.
c. It can be used as a converter
d. It is used in battery chargers.
e. It is used for phase control and heater control.
f. It is used in light dimming control circuits.
22) What is CMRR?
CMRR stands for common mode rejection ratio. It is a measure of the ability of a test instrument to reject interference that is common to both of its measurement input terminals. It is expressed in decibels and it is the ratio of the actual or common signal level appearing on the two input terminals together to the measured level.
23) What is meant by D-FF?
D Flip Flop
The D flip-flop is the most common flip-flop in use today. It is better known as delay flip-flop or data latch.
24) What is the basic difference between Latches and Flip flops?
flip flops are edge-triggered devices whereas latches are level triggered devices.
• latch does not have clock signal whereas flip flop does.
• Flip flop has two values while latch has only one value.
• (Latches do not store information, here, a bit)
25) What is a multiplexer?
A multiplexer, sometimes referred to as a "multiplexor" or simply "mux", is a device that selects between a number of input signals. In its simplest form, a multiplexer will have two signal inputs, one control input, and one output.
An everyday example of an analog multiplexer is the source selection control on a home stereo unit. Multiplexers are used in building digital semiconductors such as CPUs and graphics controllers. In these applications, the number of inputs is generally a multiple of 2 (2, 4, 8, 16, etc.), the number of outputs is either 1 or relatively small multiple of 2, and the number of control signals is related to the combined number of inputs and outputs.
26) Difference between CDMA and GSM.
The basic difference lies in the Multiplexing method used in the aerial communication i.e. from Mobile Tower to your mobile and vice versa. CDMA uses Code Division Multiple Access as the name itself indicates, for example you are in a hall occupied with number of people speaking different language. You will find that the one language you know will be heard by you and the others will be treated like noise. In the same manner each CDMA mobile communication takes place with a "code" communicating between them and the other end if one is knowing that code then only it can listen to the data being transmitted i.e. the communication is in the coded form. On the other hand GSM (Global System for Mobile Communications) uses narrowband TDMA, which allows eight simultaneous calls on the same radio frequency. TDMA works by dividing a radio frequency into time slots and then allocating slots to multiple calls. In this way, a single frequency can support multiple, simultaneous data channels.
27) Types of communications?
Analog and digital communication. As a technology, analog is the process of taking an audio or video signal (the human voice) and translating it into electronic pulses. Digital on the other hand is breaking the signal into a binary format where the audio or video data is represented by a series of "1"s and "0"s. Digital signals are immune to noise, quality of transmission and reception is good, components used in digital communication can be produced with high precision and power consumption is also very less when compared with analog signals.
28) Difference between electronic and electrical.
Electronics work on DC and with a voltage range of -48vDC to +48vDC. If the electronic device is plugged into a standard wall outlet, there will be a transformer inside which will convert the AC voltage you are supplying to the required DC voltage needed by the device. Examples: Computer, radio, T.V, etc... Electric devices use line voltage (120vAC, 240vAC, etc...). Electric devices can also be designed to operate on DC sources, but will be at DC voltages above 48v. Examples: are incandescent lights, heaters, fridge, stove, etc...
29) What is sampling?
The process of obtaining a set of samples from a continuous function of time x(t) is referred to as sampling.
30) What is cut-off frequency?
The frequency at which the response is -3dB with respect to the maximum response.
31) What is pass band?
Passband is the range of frequencies or wavelengths that can pass through a filter without being attenuated.
32) What do you mean by half-duplex and full-duplex communication? Explain briefly.
half duplex - both sender & receiver can communicate with each other, but not simultaneously...full duplex - same but simultaneous communication possible.
33) What are the flags in 8086?
Carry flag, Parity flag, Auxiliary carry flag, Zero flag, Overflow flag, Trace flag, Interrupt flag, Direction flag, and Sign flag.
34) Why crystal is a preferred clock source?
Because of high stability, large Q (Quality Factor) & the frequency that doesn’t drift with aging. Crystal is used as a clock source most of the times.
35) What does Quality factor mean?
The Quality factor is also defined, as Q. So it is a number, which reflects the lossness of a circuit. Higher the Q, the lower are the losses.
36) What are the regions in the VI characteristics of UJT?
(a). Cut-off region (b). Negative resistance region. (c). Saturation region
37) What is meant by negative resistance region of UJT?
In a UJT when the emitter voltage reaches the peak point voltage, emitter current starts flowing. After the peak point any effort to increase in emitter voltage further leads to sudden increase in the emitter current with corresponding decrease in emitter voltage, exhibiting negative resistance. This takes place until the valley point is reached. This region between the peak point and valley point is called negative resistance region.
38) Difference between mobile and a cell phone.
There is no difference, just language use, which differs from country to country, so in Britain it is called a mobile, and in USA and South Africa and other places a cell phone. Even in Europe the name differs. The Germans call it a "handy", which in English has completely another meaning as an adjective, meaning useful. In Italy it is called a telofonino or "little phone". This difference in British and American English is also evident in many other things we use every day, like lifts and elevators, nappies and diapers, pickups and trucks. The list goes on and on, any student of English has to decide which he or she will use, as the default setting.
39) What is a base station?
Base station is a radio receiver/transmitter that serves as the hub of the local wireless network, and may also be the gateway between a wired network and the wireless network.
40) How many satellites are required to cover the earth?
3 satellites are required to cover the entire earth, which is placed at 120 degree to each other. The life span of the satellite is about 15 years.
41) What is a thyristor?
Thyristor is a semiconductor device having three or more junctions .Such a device acts as a switch without any bias and can be fabricated to have voltage ratings of several hundred volts and current ratings from a few amperes to almost thousand amperes.
42) What are the types of thyristors?
· Unidirectional thyristors
· Bidirectional thyristors
· Low-power thyristors
43) Give the various triggering devices for thyristors.
· SCR
· UJT
· DIAC
· TRIAC
44) What is multiplexing?
Multiplexing (known as muxing) is a term used to refer to a process where multiple analog message signals or digital data streams are combined into one signal over a shared medium. The aim is to share an expensive resource. For example, in telecommunications, several phone calls may be transferred using one wire.
45) 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.
46) Give the other names of depletion region?
· i. space charge region
· ii. Transition region
47) What is the total current at the junction of pn junction diode?
The total in the junction is due to the hole current entering the n material and the electron current entering the p material. Total current is given by
I = Ipn(0) + Inp(0)
Where, I – Total current, Ipn(0) - hole current entering the n material, Inp(0) - electron current entering the p material.
48) State sampling theorem.
It states that, while taking the samples of a continuous signal, it has to be taken care that the sampling rate is equal to or greater than twice the cut off frequency and the minimum sampling rate is known as the Nyquist rate.
49) Explain Full duplex and half duplex.
Full duplex refers to the transmission of data in two directions simultaneously. For example, a telephone is a full-duplex device because both parties can talk at once. In contrast, a walkie-talkie is ahalf-duplex device because only one party can transmit at a time. Most modems have a switch that lets you choose between full-duplex and half-duplex modes. The choice depends on which communications program you are running. In full-duplex mode, data you transmit does not appear on your screen until it has been received and sent back by the other party. This enables you to validate that the data has been accurately transmitted. If your display screen shows two of each character, it probably means that your modem is set to half-duplex mode when it should be in full-duplex mode.
50) Give the law of electrical neutrality?
Law of electrical neutrality states Since the semiconductor is always electrically neutral, the magnitude of positive charge density must equal that of the negative charge density.
ND + p = NA + n
The application of science to the needs of humanity and a profession in which a knowledge of the mathematical and natural sciences gained by study, experience, and practice is applied with judgment to develop ways to use economically the materials and forces of nature for the benefit of mankind.
2) Define Electronic
The study and use of electrical devices that operate by controlling the flow of electrons or other electrically charged particles.
3) Define Communication
Communication means transferring a signal from the transmitter which passes through a medium then the output is obtained at the receiver (or) The transferring of message from one place to another place is called as communication.
4) What is interbase resistance of UJT?
The resistance between the two bases (B1and B2) of UJT is called as interbase resistance.
Interbase resistance = RB1 + RB2
RB1- resistance of silicon bar between B1 and emitter junction.
RB2 - resistance of silicon bar between B2 and emitter junction
5) Give the expression for peak point voltage for UJT?
VP = ή . VBB + VD
Where VP - peak point voltage, ή - intrinsic stand -off ratio, VBB - voltage applied between the bases and VD – barrier potential of UJT
6) How does a mobile work?
When you talk into a mobile telephone it converts the sound of your voice to radiofrequency energy (radio waves). The radio waves are transmitted through the air to a nearby base station. The base station then sends the call through the telephone network until it reaches the person you are calling. When you receive a call on your mobile phone the message travels through the telephone network until it reaches a base station near to you. The base station sends out radio waves, which are detected by your telephone and converted back to speech. Depending on the equipment and the operator, the frequency that each operator utilises is 900MHz, 1800MHz or 2100MHz. The mobile phone network operates on the basis of a series of cells. Each cell requires a radio base station to enable it to function. There are three types of base station and each has a particular purpose: 1. The Macrocell is the largest type and provides the main coverage for mobile phone networks. 2. The Microcell is used to improve capacity in areas where demand to make calls is high, such as shopping centres. 3. The Picocell only has a range of a few hundred metres and may be used to boost weak signals within large buildings. Each base station can only cope with a certain number of calls at any one time. So if demand exceeds the capacity of a base station an additional base station is needed.
7) What is a SCR?
A silicon controller rectifier (SCR) is a three terminal, three junction semiconductor device that acts as a true electronic switch. It is a unidirectional device. It converts alternating current into direct current and controls the amount of power fed to the load.
8) Define break over voltage of SCR.
Break over voltage is defined as the minimum forward voltage with gate open at which the SCR starts conducting heavily.
9) Why SCR cannot be used as a bidirectional switch?
SCR can do conduction only when anode is positive with respect to cathode with proper gate current. Therefore, SCR operates only in one direction and cannot be used as bidirectional switch.
10) Define demodulation-
Demodulation is the act of removing the modulation from an analog signal to get the original baseband signal back. Demodulating is necessary because the receiver system receives a modulated signal with specific characteristics and it needs to turn it to base-band.
11) What do you mean by ASCII, EBCDIC?
ASCII (American Standard Code for Information Interchange), is a character encoding based on the English alphabet. EBCDIC (Extended Binary Coded Decimal Interchange Code) is an 8-bit character encoding used on IBM mainframe operating systems
12) What do you mean by 3 dB cutoff frequency? Why is it 3 dB, not 1 dB?
3db implies 70%(o.7o7) of the power, i'e we r interested to consider the bandwidth range from peak to 70% because upto 70% its reliable. Hence 3db is called as half power freq. 3db value is the mean square value which is 70% of the maximum value.
13) What is a Ohmic contact?
An ohmic contact is a low resistance junction providing conduction in both direction between metal and the semiconductor. Ohmic contact acts as contact between any semiconductor device and outside world.
14) Give the types of ohmic contact.
(a). Non rectifying barrier (b). Tunneling barrier
15) What does UJT stands for? Justify the name UJT.
UJT stands for unijunction transistor. The UJT is a three terminal semiconductor device having two doped regions. It has one emitter terminal (E) and two base terminals (B1and B2). It has only one junction, moreover from the out look, it resembles to a transistor hence the name unijunction transistor.
16) What is a repeater?
A repeater is an electronic device that receives a signal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances without degradation.
17) What is attenuation? Attenuation is the reduction in amplitude and intensity of a signal. Signals may attenuate exponentially by transmission through a medium, or by increments calculated in electronic circuitry or set by variable controls. Attenuation is an important property in telecommunications and ultrasound applications because of its importance in determining signal strength as a function of distance. Attenuation is usually measured in units of decibels per unit length of medium (dB/cm, dB/km, etc) and is represented by the attenuation coefficient of the medium in question.
18) How do microwave oven works?
Heart of microwave oven is magnatron which generates frequency of appox. 2.4 GHz.
19) Define holding current in a SCR.
Holding current is defined as the minimum value of anode current to keep the SCR ON.
20) List the advantages of SCR.
(a). SCR can handle and control large currents.
(b). Its switching speed is very high
(c). It has no moving parts, therefore it gives noiseless operation.
(d). Its operating efficiency is high.
21) List the application of SCR.
a. It can be used as a speed controller in DC and AC motors.
b. It can be used as an inverter.
c. It can be used as a converter
d. It is used in battery chargers.
e. It is used for phase control and heater control.
f. It is used in light dimming control circuits.
22) What is CMRR?
CMRR stands for common mode rejection ratio. It is a measure of the ability of a test instrument to reject interference that is common to both of its measurement input terminals. It is expressed in decibels and it is the ratio of the actual or common signal level appearing on the two input terminals together to the measured level.
23) What is meant by D-FF?
D Flip Flop
The D flip-flop is the most common flip-flop in use today. It is better known as delay flip-flop or data latch.
24) What is the basic difference between Latches and Flip flops?
flip flops are edge-triggered devices whereas latches are level triggered devices.
• latch does not have clock signal whereas flip flop does.
• Flip flop has two values while latch has only one value.
• (Latches do not store information, here, a bit)
25) What is a multiplexer?
A multiplexer, sometimes referred to as a "multiplexor" or simply "mux", is a device that selects between a number of input signals. In its simplest form, a multiplexer will have two signal inputs, one control input, and one output.
An everyday example of an analog multiplexer is the source selection control on a home stereo unit. Multiplexers are used in building digital semiconductors such as CPUs and graphics controllers. In these applications, the number of inputs is generally a multiple of 2 (2, 4, 8, 16, etc.), the number of outputs is either 1 or relatively small multiple of 2, and the number of control signals is related to the combined number of inputs and outputs.
26) Difference between CDMA and GSM.
The basic difference lies in the Multiplexing method used in the aerial communication i.e. from Mobile Tower to your mobile and vice versa. CDMA uses Code Division Multiple Access as the name itself indicates, for example you are in a hall occupied with number of people speaking different language. You will find that the one language you know will be heard by you and the others will be treated like noise. In the same manner each CDMA mobile communication takes place with a "code" communicating between them and the other end if one is knowing that code then only it can listen to the data being transmitted i.e. the communication is in the coded form. On the other hand GSM (Global System for Mobile Communications) uses narrowband TDMA, which allows eight simultaneous calls on the same radio frequency. TDMA works by dividing a radio frequency into time slots and then allocating slots to multiple calls. In this way, a single frequency can support multiple, simultaneous data channels.
27) Types of communications?
Analog and digital communication. As a technology, analog is the process of taking an audio or video signal (the human voice) and translating it into electronic pulses. Digital on the other hand is breaking the signal into a binary format where the audio or video data is represented by a series of "1"s and "0"s. Digital signals are immune to noise, quality of transmission and reception is good, components used in digital communication can be produced with high precision and power consumption is also very less when compared with analog signals.
28) Difference between electronic and electrical.
Electronics work on DC and with a voltage range of -48vDC to +48vDC. If the electronic device is plugged into a standard wall outlet, there will be a transformer inside which will convert the AC voltage you are supplying to the required DC voltage needed by the device. Examples: Computer, radio, T.V, etc... Electric devices use line voltage (120vAC, 240vAC, etc...). Electric devices can also be designed to operate on DC sources, but will be at DC voltages above 48v. Examples: are incandescent lights, heaters, fridge, stove, etc...
29) What is sampling?
The process of obtaining a set of samples from a continuous function of time x(t) is referred to as sampling.
30) What is cut-off frequency?
The frequency at which the response is -3dB with respect to the maximum response.
31) What is pass band?
Passband is the range of frequencies or wavelengths that can pass through a filter without being attenuated.
32) What do you mean by half-duplex and full-duplex communication? Explain briefly.
half duplex - both sender & receiver can communicate with each other, but not simultaneously...full duplex - same but simultaneous communication possible.
33) What are the flags in 8086?
Carry flag, Parity flag, Auxiliary carry flag, Zero flag, Overflow flag, Trace flag, Interrupt flag, Direction flag, and Sign flag.
34) Why crystal is a preferred clock source?
Because of high stability, large Q (Quality Factor) & the frequency that doesn’t drift with aging. Crystal is used as a clock source most of the times.
35) What does Quality factor mean?
The Quality factor is also defined, as Q. So it is a number, which reflects the lossness of a circuit. Higher the Q, the lower are the losses.
36) What are the regions in the VI characteristics of UJT?
(a). Cut-off region (b). Negative resistance region. (c). Saturation region
37) What is meant by negative resistance region of UJT?
In a UJT when the emitter voltage reaches the peak point voltage, emitter current starts flowing. After the peak point any effort to increase in emitter voltage further leads to sudden increase in the emitter current with corresponding decrease in emitter voltage, exhibiting negative resistance. This takes place until the valley point is reached. This region between the peak point and valley point is called negative resistance region.
38) Difference between mobile and a cell phone.
There is no difference, just language use, which differs from country to country, so in Britain it is called a mobile, and in USA and South Africa and other places a cell phone. Even in Europe the name differs. The Germans call it a "handy", which in English has completely another meaning as an adjective, meaning useful. In Italy it is called a telofonino or "little phone". This difference in British and American English is also evident in many other things we use every day, like lifts and elevators, nappies and diapers, pickups and trucks. The list goes on and on, any student of English has to decide which he or she will use, as the default setting.
39) What is a base station?
Base station is a radio receiver/transmitter that serves as the hub of the local wireless network, and may also be the gateway between a wired network and the wireless network.
40) How many satellites are required to cover the earth?
3 satellites are required to cover the entire earth, which is placed at 120 degree to each other. The life span of the satellite is about 15 years.
41) What is a thyristor?
Thyristor is a semiconductor device having three or more junctions .Such a device acts as a switch without any bias and can be fabricated to have voltage ratings of several hundred volts and current ratings from a few amperes to almost thousand amperes.
42) What are the types of thyristors?
· Unidirectional thyristors
· Bidirectional thyristors
· Low-power thyristors
43) Give the various triggering devices for thyristors.
· SCR
· UJT
· DIAC
· TRIAC
44) What is multiplexing?
Multiplexing (known as muxing) is a term used to refer to a process where multiple analog message signals or digital data streams are combined into one signal over a shared medium. The aim is to share an expensive resource. For example, in telecommunications, several phone calls may be transferred using one wire.
45) 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.
46) Give the other names of depletion region?
· i. space charge region
· ii. Transition region
47) What is the total current at the junction of pn junction diode?
The total in the junction is due to the hole current entering the n material and the electron current entering the p material. Total current is given by
I = Ipn(0) + Inp(0)
Where, I – Total current, Ipn(0) - hole current entering the n material, Inp(0) - electron current entering the p material.
48) State sampling theorem.
It states that, while taking the samples of a continuous signal, it has to be taken care that the sampling rate is equal to or greater than twice the cut off frequency and the minimum sampling rate is known as the Nyquist rate.
49) Explain Full duplex and half duplex.
Full duplex refers to the transmission of data in two directions simultaneously. For example, a telephone is a full-duplex device because both parties can talk at once. In contrast, a walkie-talkie is ahalf-duplex device because only one party can transmit at a time. Most modems have a switch that lets you choose between full-duplex and half-duplex modes. The choice depends on which communications program you are running. In full-duplex mode, data you transmit does not appear on your screen until it has been received and sent back by the other party. This enables you to validate that the data has been accurately transmitted. If your display screen shows two of each character, it probably means that your modem is set to half-duplex mode when it should be in full-duplex mode.
50) Give the law of electrical neutrality?
Law of electrical neutrality states Since the semiconductor is always electrically neutral, the magnitude of positive charge density must equal that of the negative charge density.
ND + p = NA + n
51) What is Magnetic deflection sensitivity?
Magnetic deflection sensitivity of a cathode ray oscilloscope (CRO) is defined as the amount of deflection of electron spot produced when a magnetic flux density of 1 Wb/m2 is applied.
SM = (e / m )1\2 x 1\ (2V0) 1\2 x l x L
52) Why n - type or penta valent impurities are called as Donor impurities?
n- type impurities will donate the excess negative charge carriers ( Electrons) and therefore they are reffered to as donor impurities.
53) Why P – type or trivalent impurities are called as acceptor impurity?
p- type impurities make available positive carriers because they create holes which can accept electron, so these impurities are said to be as acceptor impurity.
54) Hall Effect-
If a metal or semiconductor carrying current I is placed in a transverse magnetic field B , an electric field E is induced in the direction perpendicular to both I and B , This phenomenon is known as Hall effect.
55) Give the expression for Hall voltage.
VH = BI / ρ w
Where VH – Hall voltage, w – width of the semiconductor, B - transverse magnetic field and I – Current across the specimen
56) Give some application of Hall Effect.
a. to measure the strength of a magnetic field in terms of electrical voltage.
b. it is used to determine whether the semiconductor is p – type or n- type material
c. it is used to determine the carrier concentration
d. it is used to determine the mobility.
57) Give the expression for the Fermi level energy in n – type semiconductor.
EF = EC – kT ln NC/ ND Where,
EF - Fermi level energy
EC – Conduction band energy
K – Boltzmann constant
T– Temperature
NC – dimension of concentration in n - type
ND - concentration of donor atoms
58) Give the expression for the Fermi level energy in n – type semiconductor.
EF = EV – kT ln NV/ NA
Where,
EF - Fermi level energy
EV – valence band energy
K – Boltzmann constant
T – Temperature
NV - dimension of concentration in p - type
NA - concentration of acceptor atoms
59) What is atomic number?
The number of protons or electrons in an atom is atomic number.
60) What is the relation for the maximum number of electrons in each shell?
2n2
61) How turning on of SCR is done?
a. By increasing the voltage across SCR above forward break over voltage.
b. By applying a small positive voltage at gate.
c. By rapidly increasing the anode to cathode voltage.
d. By irradiating SCR with light.
62) What is Shockley diode (PNPN diode)?
Shockley diode is a four layered PNPN silicon diode. It is a low- current SCR without a gate. This device is switched ON when the anode to cathode voltage is increased to forward switching voltageVS which is equivalent to SCR forward break over voltage.
63) What are valence electrons?
Electron in the outermost shell of an atom is called valence electron.
64) Which charge carriers is majority and minority carrier in N-type Semiconductor?
majority carrier: electron and minority carrier: holes.
65) What are the other names of schottky diode?
Rectifying metal semiconductor diode, Surface barrier diodes, Hot carrier diodes
66) What are hot carriers?
The injected carrier from the semiconductor to the metal is termed as hot carriers. They are so called because they possess high kinetic energy.
67) which charge carriers is majority and minority carrier in P-type Semiconductor?
Majority carrier: holes and minority carrier: electron
68) What is Barkhausen criteria?
Barkhausen criteria, without which you will not know which conditions, are to be satisfied for oscillations. “Oscillations will not be sustained if, at the oscillator frequency, the magnitude of the product of the transfer gain of the amplifier and the magnitude of the feedback factor of the feedback network (the magnitude of the loop gain ) are less than unity”. The condition of unity loop gain -Aβ = 1 is called the Barkhausencriterion. This condition implies that | Aβ|= 1and that the phase of - Aβ is zero.
69) How turning off of SCR is done?
· By reversing the polarity of anode to cathode voltage.
· By reducing the current through the SCR below holding current.
· By interrupting anode current by means of momentarily series or parallel switching
70) How does the avalanche breakdown voltage vary with temperature?
In lightly doped diode an increase in temperature increases the probability of collision of electrons and thus increases the depletion width. Thus the electrons and holes needs a high voltage to cross the junction. Thus the avalanche voltage is increased with increased temperature.
71) How does the zener breakdown voltage vary with temperature?
In heavily doped diodes, an increase in temperature increases the energies of valence electrons, and hence makes it easier for these electrons to escape from covalent bonds. Thus less voltage is sufficient to knock or pull these electrons from their position in the crystal and convert them in to conduction electrons. Thus zener break down voltage decreases with temperature.
72) Define the term transition capacitance?
When a PN junction is reverse biased, the depletion layer acts like a dielectric material while P and N –type regions on either side which has low resistance act as the plates. In this way a reverse biased PN junction may be regarded as parallel plate capacitor and thus the capacitance across this set up is called as the transition capacitance.
CT = εA / W, Where
CT - transition capacitance
ε - Permittivity of material
A - Cross section area of the junction
W – Width of the depletion region
73) What is 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.
74) Define Alloy junction.
A junction formed experimentally in which there is an abrupt change from acceptor ions on one side to donor ions on the other side is called as an alloy or fusion junction.
75) Give the expression for drift current density due to electron.
Jn = q n µnE Where,
Jn - drift current density due to electron
q- Charge of electron
µn - Mobility of electron
E - applied electric field
76) Give the expression for drift current density due to holes.
Jp = q p µp E Where,
Jn - drift current density due to holes
q - Charge of holes
µp - Mobility of holes
E - applied electric field
77) What is LED?
A PN junction diode which emits light when forward biased is known as Light emitting diode (LED).
78) Define Latching?
The ability of SCR to remain conducting even when the gate signal is removed is called as latching.
79) Define forward current rating of a SCR.
Forward current rating of a SCR is the maximum anode current that it can handle without destruction.
80) List the important ratings of SCR.
o Forward break over voltage
o Holding current
o Gate trigger current
o Average forward current
o Reverse break down voltage.
81) What is a TRIAC?
TRIAC is a three terminal bidirectional semiconductor switching device. It can conduct in both the directions for any desired period. In operation it is equivalent to two SCR’s connected in antiparallel.
82) Give the application of TRIAC.
(a) Heater control (b). Motor speed control (c). Phase control (d). Static switches
83)What are the different operating modes of TRIAC?
Keeping MT2 and G positive
Keeping MT2 and G negative.
Keeping MT2 positive and G negative.
Keeping MT2 negative and G positive.
84) What is stop band?
A stopband is a band of frequencies, between specified limits, in which a circuit, such as a filter or telephone circuit, does not let signals through, or the attenuation is above the required stopband attenuation level.
85) Explain AM and FM.
AM-Amplitude modulation is a type of modulation where the amplitude of the carrier signal is varied in accordance with the information bearing signal. FM-Frequency modulation is a type of modulation where the frequency of the carrier signal is varied in accordance with the information bearing signal.
86) Where do we use AM and FM?
AM is used for video signals for example TV. Ranges from 535 to 1705 kHz.
FM is used for audio signals for example Radio. Ranges from 88 to 108 MHz.
87) Advantages of negative feedback over positive feedback?
Much attention has been given by researchers to negative feedback processes, because negative feedback processes lead systems towards equilibrium states. Positive feedback reinforces a given tendency of a system and can lead a system away from equilibrium states, possibly causing quite unexpected results.
88) Example for negative feedback and positive feedback.
Example for –ve feedback is ---Amplifiers and for +ve feedback is – Oscillators
89) What is resistor?
A resistor is a two-terminal electronic component that opposes anelectric current by producing a voltage drop between its terminals in proportion to the current, that is, in accordance with Ohm's law: V= IR.
90) What is conductor?
A substance, body, or device that readily conducts heat, electricity, sound, etc. Copper is a good conductor of electricity.
91) Mention the applications of UJT
It is used in timing circuits
It is used in switching circuits
It is used in phase control circuits
It can be used as trigger device for SCR and triac.
It is used in saw tooth generator.
It is used for pulse generation.
92) What is an Amplifier?
An electronic device or electrical circuit that is used to boost (amplify) the power, voltage or current of an applied signal.
93) 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.
94) What is a semi conductor?
A semiconductor is a solid material that has electrical conductivity in between that of a conductor and that of an insulator (An Insulator is a material that resists the flow of electric current. It is an object intended to support or separate electrical conductors without passing current through itself); it can vary over that wide range either permanently or dynamically.
95) What is diode?
In electronics, a diode is a two-terminal device. Diodes have two active electrodes between which the signal of interest may flow, and most are used for their unidirectional current property.
96) What is transistor?
In electronics, a transistor is a semiconductor device commonly used to amplify or switch electronic signals. The transistor is the fundamental building block of computers, and all other modern electronic devices. Some transistors are packaged individually but most are found in integrated circuits.
97) What is intrinsic stand- off ratio of an UJT?
If a voltage VBB is applied between the bases with emitter open the circuit will behave as
a potential divider. Thus the voltage VBB will be divided across RB1 and RB2
Voltage across resistance RB1,
V1 = RB1 * VBB = RB1 * VBB = ή * VBB
RB1 + RB2 RBB
The resistance ratio ή = RB1 / RBB is known as intrinsic stand -off ratio.
98) What is a feedback? explain different types of feedback.
Feedback is a process whereby some proportion of the output signal of a system is passed (fed back) to the input. This is often used to control the dynamic behaviour of the system. Types of feedback:
(a) Negative feedback: This tends to reduce output (but in amplifiers, stabilizes and linearizes operation). Negative feedback feeds part of a system's output, inverted, into the system's input; generally with the result that fluctuations are attenuated.
(b) Positive feedback: This tends to increase output. Positive feedback, sometimes referred to as "cumulative causation", is a feedback loop system in which the system responds to perturbation (Aperturbation means a system, is an alteration of function, induced by external or internal mechanisms) in the same direction as the perturbation. In contrast, a system that responds to the perturbation in the opposite direction is called a negative feedback system. Bipolar feedback: which can either increase or decrease output.
99) What is Oscillator?
An oscillator is a circuit that creates a waveform output from a direct current input. The two main types of oscillator are harmonic and relaxation. The harmonic oscillators have smooth curved waveforms, while relaxation oscillators have waveforms with sharp changes.
100) What is forbidden energy gap?
The space between the valence and conduction band is said to be forbidden energy gap.
Magnetic deflection sensitivity of a cathode ray oscilloscope (CRO) is defined as the amount of deflection of electron spot produced when a magnetic flux density of 1 Wb/m2 is applied.
SM = (e / m )1\2 x 1\ (2V0) 1\2 x l x L
52) Why n - type or penta valent impurities are called as Donor impurities?
n- type impurities will donate the excess negative charge carriers ( Electrons) and therefore they are reffered to as donor impurities.
53) Why P – type or trivalent impurities are called as acceptor impurity?
p- type impurities make available positive carriers because they create holes which can accept electron, so these impurities are said to be as acceptor impurity.
54) Hall Effect-
If a metal or semiconductor carrying current I is placed in a transverse magnetic field B , an electric field E is induced in the direction perpendicular to both I and B , This phenomenon is known as Hall effect.
55) Give the expression for Hall voltage.
VH = BI / ρ w
Where VH – Hall voltage, w – width of the semiconductor, B - transverse magnetic field and I – Current across the specimen
56) Give some application of Hall Effect.
a. to measure the strength of a magnetic field in terms of electrical voltage.
b. it is used to determine whether the semiconductor is p – type or n- type material
c. it is used to determine the carrier concentration
d. it is used to determine the mobility.
57) Give the expression for the Fermi level energy in n – type semiconductor.
EF = EC – kT ln NC/ ND Where,
EF - Fermi level energy
EC – Conduction band energy
K – Boltzmann constant
T– Temperature
NC – dimension of concentration in n - type
ND - concentration of donor atoms
58) Give the expression for the Fermi level energy in n – type semiconductor.
EF = EV – kT ln NV/ NA
Where,
EF - Fermi level energy
EV – valence band energy
K – Boltzmann constant
T – Temperature
NV - dimension of concentration in p - type
NA - concentration of acceptor atoms
59) What is atomic number?
The number of protons or electrons in an atom is atomic number.
60) What is the relation for the maximum number of electrons in each shell?
2n2
61) How turning on of SCR is done?
a. By increasing the voltage across SCR above forward break over voltage.
b. By applying a small positive voltage at gate.
c. By rapidly increasing the anode to cathode voltage.
d. By irradiating SCR with light.
62) What is Shockley diode (PNPN diode)?
Shockley diode is a four layered PNPN silicon diode. It is a low- current SCR without a gate. This device is switched ON when the anode to cathode voltage is increased to forward switching voltageVS which is equivalent to SCR forward break over voltage.
63) What are valence electrons?
Electron in the outermost shell of an atom is called valence electron.
64) Which charge carriers is majority and minority carrier in N-type Semiconductor?
majority carrier: electron and minority carrier: holes.
65) What are the other names of schottky diode?
Rectifying metal semiconductor diode, Surface barrier diodes, Hot carrier diodes
66) What are hot carriers?
The injected carrier from the semiconductor to the metal is termed as hot carriers. They are so called because they possess high kinetic energy.
67) which charge carriers is majority and minority carrier in P-type Semiconductor?
Majority carrier: holes and minority carrier: electron
68) What is Barkhausen criteria?
Barkhausen criteria, without which you will not know which conditions, are to be satisfied for oscillations. “Oscillations will not be sustained if, at the oscillator frequency, the magnitude of the product of the transfer gain of the amplifier and the magnitude of the feedback factor of the feedback network (the magnitude of the loop gain ) are less than unity”. The condition of unity loop gain -Aβ = 1 is called the Barkhausencriterion. This condition implies that | Aβ|= 1and that the phase of - Aβ is zero.
69) How turning off of SCR is done?
· By reversing the polarity of anode to cathode voltage.
· By reducing the current through the SCR below holding current.
· By interrupting anode current by means of momentarily series or parallel switching
70) How does the avalanche breakdown voltage vary with temperature?
In lightly doped diode an increase in temperature increases the probability of collision of electrons and thus increases the depletion width. Thus the electrons and holes needs a high voltage to cross the junction. Thus the avalanche voltage is increased with increased temperature.
71) How does the zener breakdown voltage vary with temperature?
In heavily doped diodes, an increase in temperature increases the energies of valence electrons, and hence makes it easier for these electrons to escape from covalent bonds. Thus less voltage is sufficient to knock or pull these electrons from their position in the crystal and convert them in to conduction electrons. Thus zener break down voltage decreases with temperature.
72) Define the term transition capacitance?
When a PN junction is reverse biased, the depletion layer acts like a dielectric material while P and N –type regions on either side which has low resistance act as the plates. In this way a reverse biased PN junction may be regarded as parallel plate capacitor and thus the capacitance across this set up is called as the transition capacitance.
CT = εA / W, Where
CT - transition capacitance
ε - Permittivity of material
A - Cross section area of the junction
W – Width of the depletion region
73) What is 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.
74) Define Alloy junction.
A junction formed experimentally in which there is an abrupt change from acceptor ions on one side to donor ions on the other side is called as an alloy or fusion junction.
75) Give the expression for drift current density due to electron.
Jn = q n µnE Where,
Jn - drift current density due to electron
q- Charge of electron
µn - Mobility of electron
E - applied electric field
76) Give the expression for drift current density due to holes.
Jp = q p µp E Where,
Jn - drift current density due to holes
q - Charge of holes
µp - Mobility of holes
E - applied electric field
77) What is LED?
A PN junction diode which emits light when forward biased is known as Light emitting diode (LED).
78) Define Latching?
The ability of SCR to remain conducting even when the gate signal is removed is called as latching.
79) Define forward current rating of a SCR.
Forward current rating of a SCR is the maximum anode current that it can handle without destruction.
80) List the important ratings of SCR.
o Forward break over voltage
o Holding current
o Gate trigger current
o Average forward current
o Reverse break down voltage.
81) What is a TRIAC?
TRIAC is a three terminal bidirectional semiconductor switching device. It can conduct in both the directions for any desired period. In operation it is equivalent to two SCR’s connected in antiparallel.
82) Give the application of TRIAC.
(a) Heater control (b). Motor speed control (c). Phase control (d). Static switches
83)What are the different operating modes of TRIAC?
Keeping MT2 and G positive
Keeping MT2 and G negative.
Keeping MT2 positive and G negative.
Keeping MT2 negative and G positive.
84) What is stop band?
A stopband is a band of frequencies, between specified limits, in which a circuit, such as a filter or telephone circuit, does not let signals through, or the attenuation is above the required stopband attenuation level.
85) Explain AM and FM.
AM-Amplitude modulation is a type of modulation where the amplitude of the carrier signal is varied in accordance with the information bearing signal. FM-Frequency modulation is a type of modulation where the frequency of the carrier signal is varied in accordance with the information bearing signal.
86) Where do we use AM and FM?
AM is used for video signals for example TV. Ranges from 535 to 1705 kHz.
FM is used for audio signals for example Radio. Ranges from 88 to 108 MHz.
87) Advantages of negative feedback over positive feedback?
Much attention has been given by researchers to negative feedback processes, because negative feedback processes lead systems towards equilibrium states. Positive feedback reinforces a given tendency of a system and can lead a system away from equilibrium states, possibly causing quite unexpected results.
88) Example for negative feedback and positive feedback.
Example for –ve feedback is ---Amplifiers and for +ve feedback is – Oscillators
89) What is resistor?
A resistor is a two-terminal electronic component that opposes anelectric current by producing a voltage drop between its terminals in proportion to the current, that is, in accordance with Ohm's law: V= IR.
90) What is conductor?
A substance, body, or device that readily conducts heat, electricity, sound, etc. Copper is a good conductor of electricity.
91) Mention the applications of UJT
It is used in timing circuits
It is used in switching circuits
It is used in phase control circuits
It can be used as trigger device for SCR and triac.
It is used in saw tooth generator.
It is used for pulse generation.
92) What is an Amplifier?
An electronic device or electrical circuit that is used to boost (amplify) the power, voltage or current of an applied signal.
93) 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.
94) What is a semi conductor?
A semiconductor is a solid material that has electrical conductivity in between that of a conductor and that of an insulator (An Insulator is a material that resists the flow of electric current. It is an object intended to support or separate electrical conductors without passing current through itself); it can vary over that wide range either permanently or dynamically.
95) What is diode?
In electronics, a diode is a two-terminal device. Diodes have two active electrodes between which the signal of interest may flow, and most are used for their unidirectional current property.
96) What is transistor?
In electronics, a transistor is a semiconductor device commonly used to amplify or switch electronic signals. The transistor is the fundamental building block of computers, and all other modern electronic devices. Some transistors are packaged individually but most are found in integrated circuits.
97) What is intrinsic stand- off ratio of an UJT?
If a voltage VBB is applied between the bases with emitter open the circuit will behave as
a potential divider. Thus the voltage VBB will be divided across RB1 and RB2
Voltage across resistance RB1,
V1 = RB1 * VBB = RB1 * VBB = ή * VBB
RB1 + RB2 RBB
The resistance ratio ή = RB1 / RBB is known as intrinsic stand -off ratio.
98) What is a feedback? explain different types of feedback.
Feedback is a process whereby some proportion of the output signal of a system is passed (fed back) to the input. This is often used to control the dynamic behaviour of the system. Types of feedback:
(a) Negative feedback: This tends to reduce output (but in amplifiers, stabilizes and linearizes operation). Negative feedback feeds part of a system's output, inverted, into the system's input; generally with the result that fluctuations are attenuated.
(b) Positive feedback: This tends to increase output. Positive feedback, sometimes referred to as "cumulative causation", is a feedback loop system in which the system responds to perturbation (Aperturbation means a system, is an alteration of function, induced by external or internal mechanisms) in the same direction as the perturbation. In contrast, a system that responds to the perturbation in the opposite direction is called a negative feedback system. Bipolar feedback: which can either increase or decrease output.
99) What is Oscillator?
An oscillator is a circuit that creates a waveform output from a direct current input. The two main types of oscillator are harmonic and relaxation. The harmonic oscillators have smooth curved waveforms, while relaxation oscillators have waveforms with sharp changes.
100) What is forbidden energy gap?
The space between the valence and conduction band is said to be forbidden energy gap.