ELECTRONICS AND COMMUNICATION PAGE 2
Contributed by Mercy Benyl
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?
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
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.
