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DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

TWO MARKS QUESTIONS & ANSWERS

EC2151 -- ELECTRIC CIRCUITS AND ELECTRON DEVICES

1

DHIRAJ LAL GANDHI COLLEGE OF TECHNOLOGY


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4 0 0 100

SYLLABUSEC2151- ELECTRIC CIRCUITS AND ELECTRON DEVICES

(For ECE, CSE, IT and Biomedical Engg. Branches)

UNIT I CIRCUIT ANALYSIS TECHNIQUES 12

Kirchoffs current and voltage laws series and parallel connection of independent sources R, L and C

Network Theorems Thevenin, Superposition, Norton, Maximum power transfer and duality Star-deltaconversion.

UNIT II TRANSIENT RESONANCE IN RLC CIRCUITS 12

Basic RL, RC and RLC circuits and their responses to pulse and sinusoidal inputs frequency response

Parallel and series resonances Q factor single tuned and double tuned circuits.

UNIT III SEMICONDUCTOR DIODES 12

Review of intrinsic & extrinsic semiconductors Theory of PN junction diode Energy band structure

current equation space charge and diffusion capacitances effect of temperature and breakdown mechanism

Zener diode and its characteristics.

UNIT IV TRANSISTORS 12

Principle of operation of PNP and NPN transistors study of CE, CB and CC configurations and comparison

of their characteristics Breakdown in transistors operation and comparison of N-Channel and P-Channel

JFET drain current equation MOSFET Enhancement and depletion types structure and operation

comparison of BJT with MOSFET thermal effect on MOSFET.

UNIT V SPECIAL SEMICONDUCTOR DEVICES

(Qualitative Treatment only) 12

Tunnel diodes PIN diode, varactor diode SCR characteristics and two transistor equivalent model UJT

Diac and Triac Laser, CCD, Photodiode, Phototransistor, Photoconductive and Photovoltaic cells LED,

LCD.

TOTAL: 60 PERIODS

TEXT BOOKS:

1. Joseph A. Edminister, Mahmood, Nahri, Electric Circuits Shaum series,Tata McGraw Hill

(2001)

2. S. Salivahanan, N. Suresh kumar and A. Vallavanraj, Electronic Devices and Circuits,Tata McGrawHill, 2nd Edition, (2008).

3. David A. Bell, Electronic Devices and Circuits, Oxford University Press, 5th Edition, (2008).

REFERENCES:

1. Robert T. Paynter, Introducing Electronics Devices and Circuits, Pearson Education, 7th Education(2006).

2. William H. Hayt, J.V. Jack, E. Kemmebly and steven M. Durbin, Engineering Circuit Analysis,TataMcGraw Hill, 6th Edition, 2002.

3. J. Millman & Halkins, Satyebranta Jit, Electronic Devices & Circuits,Tata McGraw Hill, 2n

Edition, 2008.

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UNIT I

ELECTRIC CIRCUITS AND ELECTRON DEVICES

1. What is charge?

The charge is an electrical property of the atomic particles of which matter consists. The

unit of charge is the coulomb.

2. Define current?

The flow of free electrons in a metal is called electric current. The unit of current is theampere. Current (I) = Q/t, Where Q is total charge transferred & T is time required

for transfer of charge.

3. What is voltage?

The potential difference between two points in an electric circuit called voltage. The unit

of voltage is volt. It is represented by V OR v.

Voltage = W/Q = workdone/Charge

4. Define power.

The rate of doing work of electrical energy or energy supplied per unit time is called thepower. The power denoted by either P of p. It is measured in Watts. (W).

Power = work done in electric circuit/Time

P = dw/dt = dw/dq.dq/dtP = VI

5. What is network?

Interconnection of two or more simple circuit elements is called an electric network.

6. Distinguish between a branch and a node of a circuit.

A part of the network which connects the various points of the network with one anotheris called a branch. A point at which two or more elements are jointed together is called

node.

7. Distinguish between a mesh and a Loop of a circuit.

A mesh is a loop that does not contain other loops. All meshed are loops. But all loops

are not meshes. A loop is any closed path of branches.

8. Define active and passive elements.

The sources of energy are called active element.

Example: voltage source, current source.The element which stores or dissipates energy is called passive element.

Example: Resistor, Inductor, Capacitor.

9. Define unilateral and bilateral elements.

In unilateral element, voltage current relation is not same for both the direction.

Example: Diode, Transistors.In bilateral element, voltage current relation is same for both the direction.

Example: Resistor

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10. Define linear and non-linear elements.

If the element obeys superposition principle, then it is said to be linear elements.

Example: Resistor.If the given network is not obeying superposition principle then it is said to be non linear

elements.

Example: Transistor, Diode.

11. Define Lumped and distributed elements.

Physically separable elements are called Lumped element.Example : Resistor, Capacitor, Inductor.

A distributed element is one which is not separable for electrical purpose.

Example : Transmission line has distributor resistance, capacitance and inductance.

12. How are the electrical energy sources classified?

The electrical energy sources are classified into:

1. Ideal voltage source 2. Ideal current source.

13. Define an ideal voltage source.

The voltage generated by the source does not vary with any circuit quantity. It is only afunction of time. Such a source is called an ideal voltage source.

14. Define an ideal current source.

The current generated by the source does not vary with any circuit quantity.

It is only a function of time. Such a source is called as an ideal current source.

15. What are independent source?

Independent sources are those in which, voltage and current are independent and are not

affected by other part of the circuit.

16. What are dependent sources?

Dependent sources are those in which source voltage or current is not fixed, but is

dependent on the voltage or current existing at some other location in the circuit.

17. What are the different types of dependent or controlled sources?

1. Voltage Controlled Voltage Sources (VCVS)2. Current Controlled Voltage Sources (CCVS)

3. Voltage Controlled Current Sources (VCCS)

4. Current Controlled Current Sources (CCCS)

18. What is resistance?

It is the property of a substance which opposes the flow of current through it. The

resistance of element is denoted by the symbol R. It is measured in Ohms.R = PL / A

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19. Write down the V-I relationship of circuit elements.

Circuit

Element

Voltage Current Power

Resistance V = iR i = V / R P = vi

Inductance V = L di /dt i = 1/L vdt P = Li di / dt

Capacitance V = 1/c idt i = C dv / dt P = CV dv / dt

20. What is average value?

It is defined as area under one complete cycle to period.

The average value of the sine wave is the total area under the half-cycle curve divided bythe distance of the curve.Area under one complete cycle

Average value = _____________________________Period

21. Define R.M.S. value.

The r.m.s value may be determined by taking the mean of the squares of theinstantaneous value of current over one complete cycle.

(Area under hatched line)

RMS = ______________________ Period

22. Define form factor.

The ratio of RMS value to the average value is called the Form factor.

RMS valueForm factor (Kf) = ______________

Average Value

23. Define peak factor.

Peak factor is defined as the ratio of the maximum value to the rms value.Maximum value

Peak Factor (Kp) = ________________RMS value

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24. Define Ohms law.

The current flowing through the electric circuit is directly proportional to the potential

difference across the circuit and inversely proportional to the resistance of the circuit,provided the temperature remains constant.

25. Define Kirchoffs current law.Kirchhoffs current law states that in a node, sum of entering current is equal sum of

leaving current.

I at junction point = 0

26. Define Kirchoffs voltage law.

Kirchhoffs Voltage Law (KVL) states that the algebraic sum of the voltages around anyclosed path is zero.

Around a closed path V = 0.

27. Two resistances with equal value of R are connected in series and parallel. What

is the equivalent resistance?Resistance in series R eq = R1+R2

R1R2

Resistance in parallel R eq = __________

R1+R2

28. Two inductors with equal value of L are connected in series and parallel what is

the equivalent inductance?

Inductance in series L eq = L1 + L2

L1L2

Inductance in parallel L eq = _______ L1+L2

29. Two capacitors with equal value of C are connected in series and parallel. What

is the equivalent capacitance?

C1C2Capacitance in series C eq = ____________

C1+C2

Capacitance in parallel C eq = C1 + C2

30. Write down the formula for a star connected network is converted into a delta

network?R R + R R + R R

A B B C C A

R = ____________________________AB R

C

R R + R R + R R

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A B B C C A

R = ____________________________

BC RA

R R + R R + R R

A B B C C AR = ____________________________

CA R

B

31. Write down the formula for a delta connected network is converted into a star

network?

R * R

AB CA

R = ____________________________

AB

R + R + RAB BC CA

R * R

AB BCR = _____________________________

B

R

AB

R * RBC CA

R = _____________________________

BR

AB

Where R = R + R + R

AB AB BC CA

32. Write few advantages of sinusoid waveform?

1. The response of the sinusoidal input for second order system is sinusoidal.

2. The wave form can be written in terms of sinusoidal function according to fourier

theorem.3. The derivatives and integral also sinusoidal.

4. Easy for analyses.

5. Easy to generate.6. More useful in power industry.

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33. Distinguish between a cycle, time periods and frequency.

One complete set of positive and negative instantaneous values of the voltageor current is called cycle.

The time taken by an alternating quantity to complete one cycle is called timeperiod (T).2

Time period (T) = _________ W

The number of cycle that a alternating quantity completed per second is known asfrequency. It is measured in HZ.

1Frequency (f) = ________

T

34. What is instantaneous value?The value of an alternating current, at any particular moment is called itsinstantaneous value.

35. What are peak value and peak to peak value?

The peak value of the sine wave during positive or negative half only.The sum of positive and negative value is called a peak to peak value. The

peak to peak value of a sinusoidal alternating voltage is equal to two times the peak value.

36. What is average value?

The average value of the sine wave is the total area under the half-cycle curvedivided by the distance of the curve.

1 TV = ___ V (t) dtav T 0

37. Define effective value or RMS value of a sinusoidal voltage.

The R.M.S value may be determined by taking the mean of the squares of theInstantaneous value of current over one complete cycle. This is often known

as the effective value.V = ____________

rms 1/T T 2 [V (t) dt0

38. Define phasor.

Graphical representation of phasors V = Vm


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It is denoted as Z and it is measured in Ohms.

VImpedance (Z) = ____

I

41. Obtain the equivalent impedance and reactances for series and parallel connections.

Impedance in series Z = Z + Z

eq 1 2

Impedance in parallel Z = Z Zeq 1 2

_________

Z1 + Z2

Reactances in series j X = j (X + X)eq 1 2

X X

1 2Reactances in parallel j X = j ____________

eq X + X

1 2

41. Define admittance.

The reciprocal of impedance is called admittance. It is denoted as Y and it is measured

in Siemens (S).

1 1

Admittance (Y) = ___ = ___ Z V

42. Obtain the equivalent admittance for series and parallel connections.

Y Y

1 2

Admittance in series Y = ____________eq Y Y

1 2

Admittance in parallel Y = Y Y

Eq 1 2

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43. Obtain the equivalent conductance and susceptance for series and parallel

connections.

G G

Conductance in series G = 1 2

eq _________ G + G

1 2

Conductance in parallel G = G + GEq 1 2

B B

Susceptance in series jB 1 2

eq = __________

G + G

1 2

j(B B )Susceptance in parallel jB 1 2

eq =

44. Define phasor diagram.

The phasor diagram is a name given to a sketch in the complex plane showing the

relationships of the phasor voltages and phasor currents throughout a specific circuit.

45. What is instantaneous power?

The power at any instant of time is known as instantaneous power.

P (t) = v(t) . I (t)

46. What is average power?

The average of the instantaneous power over one period is called average power. Averagepower is also defined as the product of voltage and current.

47. What is apparent power?

The product of V and I is known as the apparent power (s).

rms rms

Apparent power (S) = V I VA

Eff eff

48. Define power factor.

The ratio of the average power to the apparent power is called the power factor.

Average power

Power Factor = _________________Apparent Power

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49. What is power triangle ?

A commonly employed graphical representation of complex power is known as the

power triangle.

50. Define complex power

The product of the rms voltage phasor and the complex conjugate of the rms current

phasor is known as complex power. It is denoted as S and it is measured in volt-amperes (VA)

1

The complex power is S = ___ vi*

2

51. What is reactive power?

It is defined as product of the applied voltage and the reactive component of the current.

It is also called as imaginary component of the apparent power. It is represented by Q and it is

measured in unit volt- ampere reactive (VAR).Q = V I sin VAR

Eff eff

52 What is the equation for determining the number of independent loops in mesh

current method?

L = b-n +1

Where L = number of loops

B = number of branches

N = number of nodes.

52. On which law is the mesh analysis based?

Mesh analysis is based on Kirchoffs voltage law.

53. On which law is the nodal analysis based?

Nodal analysis is based on Kirchoffs current law and Ohms law.

54. What is mesh analysis?

Mesh analysis is one of the basic techniques used for finding current flowing through theloop in a network.

Mesh analysis is applicable if the given network contains voltage sources. If therer exist

current sources in a circuit, then it should be converted into equivalent voltage sources.

55. What is nodal analysis?

Nodal analysis is one of the basic techniques used to finding solution for voltage drop

across the nodes in a given circuit.Nodal analysis is applicable if the given network contains current sources. If there exists

voltage sources in the given circuit, then it can to be converted into equivalent current sources.

56. When do we go for supermesh analysis.

If the branches in the network has a current source, then it is slightly difficult to apply mesh

analysis.

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One way to over come this difficulty is by applying the supermesh technique.

In this case we have to choose supermesh.

A supermesh is constituted by two adjacent loops that have common current source.

57. When do we, go for supernode analysis.

If the branches in the network has a voltage source, then it is slightly difficult to apply nodal

analysis.

One way to overcome this difficulty is by applying the supernode technique.

In this case, we have to choose super node.

A supernode is constituted by two adjacent node that have common voltage source.

58. State superposition theorem.

Any electric circuit (linear, lumped, bilateral), is energeied by two or more sources,

the response in any element in the network is equal to the algebraic sum of the responses caused by

individual sources acting separately.

59. State Thevenins Theorem.

A complex network having linear, bilateral, lumped elements with open circuited

output terminals can be reduced by a simple circuit consisting of a single voltage source in series

with a impedance.

60. State Nortons theorem.

Any electrical network (linear, lumped, bilateral) with short circuited terminals can be

reduced by a simple circuit consisting of a single current source in parallel with a Theveninsequivalent resistance.

61. State Maximum power transfer theorem.

Power transferred from source to load will be maximum, when source resistance is

equal to load resistance looking back from its load terminals.

62. Define duality.

Two electrical network which are governed by the same type of equations are called

duality.

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UNIT II

TRANSIENT RESONANCE IN RLC CIRCUITS

1. What is transient state?If a network contains energy storage elements, with change in excitation, the currentand voltages change from one state to other state. The behaviour of the voltage or current when it ischanged from one state to another state is called transient state.

2. What is transient time?

The time taken for the circuit to change from one steady state to another steady stateis called transient time.

3. What is natural response?If we consider a circuit containing storage elements which are independent of

sources, the response depends upon the nature of the circuit, it is called natural response.4. What is transient response?

The storage elements deliver their energy to the resistances, hence the responsechanges with time, gets saturated after sometime, and is referred to the transient response.

5. Define Laplace transform function.

The laplace transform of any time dependent functionf (t) is given by F (s).Where SA complex frequency given by S = + jw

-stF (S) = L [F (T) ] = F (t) e dt

06. What is inverse Laplace transform?

Inverse Laplace Transform permits going back in the reverse direction i.e. from sdomain to time domain.

-1 1 1 + j stL [F(s)] = f (t) = _________ F (s) e ds

2j 1 - j

7. Define time constant or RL Circuit.

The time taken to reach 63.2% of final value in a RL Circuit is called the timeconstant of RL circuit.Time constant (t) = L / R

8. Define time constant of RC Circuit.

The time taken to reach 36.8% of initial current in an RC circuit is called the timeconstant of RC circuit.

Time constant (t) = RC.

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9. What is meant by natural frequency?

If the damping is made zero then the response oscillates with natural frequency without anyopposition, such a frequency is called natural frequency of oscillations, denoted as

n.10. Define damping ratio.

It is the ratio of actual resistance (R) in the circuit to the critical resistance (R cr). It isdenoted by greek letter Zeta ().R R

= ____ = _____ C / LRcr 2

11. Define initial value theorem.

The initial value theorem states that if f (t) and f (t) both are laplace transformable,Then

Lim f (t) = lim s F (s)

T

0 s

12. Define final value theorem.

The final value theorem states that, if f (t) and f (t) both are laplace transformable,then

Lim f (t) = lim s F (s)T s 0

13. What is driving point impedence ?

The ratio of the Laplace transform of the voltage at the point to the laplace transform of thecurrent at the same port is called driving point impedance.

The driving point impedance of the network is define asV(s)Z (S) = _____________

I (s)

14. What is transfer point impedance?It is defined as the ratio of voltage transform at one port to the current transform at the

other port. It is defined byV (s)

Z (s) = ___2_________ 21 I (s)

1andV (s)

Z (s) = ___1_________ 12 I (s)

2

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15. Define network function.

A network function N (S) is defined as the ratio of the complex amplitude of anexcponential output P (S) to the complex amplitude of an exponential input Q (S).

16. Define pole and zero.

The network function N (S) will become infinite. Hence the roots of denominatorpolynomial P1, P2, P3,Pm are called poles of network function.The network function N(S) will become zero. Hence the roots of numerator

polynomial Z1, Z2, Z3..Zn. are called zeros of network function.

17. Define resonant circuit.

The circuit that treat a narrow range of frequencies very differently than all otherfrequencies. These are referred to as resonant circuit. The gain of a highly resonant circuit attains asharp maximum or minimum as its resonant frequency.

18. When the circuit is said to be in resonance?

1. A network is in resonance when the voltage and current at the network input terminals arein phase.2. If inductive reactance of a network equals capacitive reactance then the network is said to

be resonance

19. What is resonant frequency ?The frequency at which resonance occurs is called resonance frequency.

1f = ________ r 2LC

20. Define bandwidth.

The bandwidth (BW) is defined as the frequency difference between upper cut-offfrequency (f2) and lower cut-off frequency (f1)

Bandwidth = f2-f1Where f2 upper cut-off frequency

F1 lower cut-off frequency

21. Define selectivity.

Selectivity is defined as the ratio of bandwidth to the resonant frequency of resonantcircuit.

Bandwidth

Selectivity = _______________________ Resonant frequency

22. Define quality factor.

The quality factor is defined as the ratio of maximum energy stored to the energydissipated per cycle.

Maximum energy stored per cycleQuality factor (Q) = 2 * ______________________________

Energy dissipated per cycle

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23. Define half power frequencies ?

The frequencies at which the power is half the maximum power are called half powerfrequencies.

RLower half power frequency, f1 = f r - ____

4 LR

Upper half power frequency, f2 = f r + ____4 L

24. Write down the formula for inductive reactance and capacitive reactance?

Inductive reactance is given by X = 2 flL

1Capacitive reactance is given by X = _________C 2 fc

WhereF supply frequencyL Inductance of the coilC Capacitance of the capacitor.

25. Give the expression for quality factor of series RLC Circuit.

Quality factor is Q = 1 / R L /C

26. Give the expression for quality factor of parallel RLC Circuit.Quality factor is Q = R C / L

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UNIT III

SEMICONDUCTOR DIODES

1. Give the value of Charge, Mass of an electron.

Charge of an electron 1.6 x 10 -19 coloumbs & Mass of an electron - 9.11 x 10 -31 Kgs2. Define Potential.

Apotential of V volts at point B with respect to point A, is defined as the work

done in taking unit positive charge from A to B , against the electric field.

3. Define Current density.

It is defined as the current per unit area of the conducting medium. J = I / A

4. Define Electron volts.

If an electron falls through a potential of one volt then its energy is 1 electron volt.

1 eV = 1.6 x 10 -19 joules

5. What is Electrostatic deflection sensitivity?

Electrostatic deflection sensitivity of a pair of deflecting plates of a cathode ray

oscilloscope ( CRO) is defined as the amount of deflection of electron spotproduced when a voltage of 1 Volt DC is applied between the corresponding plates.

6. What is the relation for the maximum number of electrons in each shell?

Ans: 2n2

7. What are valence electrons?

Electron in the outermost shell of an atom is called valence electron.

8. What is forbidden energy gap?

The space between the valence and conduction band is said to be forbidden energy gap.

9. What are conductors? Give examples?

Conductors are materials in which the valence and conduction band overlap each other so there is aswift movement of electrons which leads to conduction. Ex. Copper, silver.

10. What are insulators? Give examples?

Insulators are materials in which the valence and conduction band are far awayfrom each other. So no movement of free electrons and thus no conduction.

Ex glass, plastic.

11. Give the energy band structure of Insulator.

In Insulators there is a wide forbidden energy gap. So movement of valence

electron from valence to conduction band is not possible.

12. Give the energy band structure of Semi conductor.

In Semiconductors there is a small forbidden energy gap. So movement of

valence electron from valence to conduction band is possible if the valence

electrons are supplied with some energy.

13. Give the energy band structure of conductor.

In conductors there is no forbidden energy gap, valence band and conduction

and over lap each other. so there is a heavy movement of valence electrons.

14. what are Semiconductors? Give examples?

The materials whose electrical property lies between those of conductors and

insulators are known as Semiconductors. Ex germanium, silicon.

15. What are the types of Semiconductor?

1. Intrinsic semiconductor 2. Extrinsic semiconductor.

16. What is Intrinsic Semiconductor?

Pure form of semiconductors are said to be intrinsic semiconductor.

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Ex: germanium, silicon.

17. Define Mass action law.

Under thermal equilibrium the product of free electron concentration (n) and holeconcentration (p) is constant regardless of the individual magnitude.

n.p = ni2

18. What is Extrinsic Semiconductor?If certain amount of impurity atom is added to intrinsic semiconductor the

resulting semiconductor is Extrinsic or impure Semiconductor.

19. What are the types of Extrinsic Semiconductor?

1. P-type Semiconductor

2. N- Type Semiconductor.

20. What is P-type Semiconductor?

The Semiconductor which are obtained by introducing pentavalent impurity atom

(phosphorous, antimony) are known as P-type Semiconductor.

21. What is N-type Semiconductor?

The Semiconductor which is obtained by introducing trivalent impurity atom (gallium, indium) are

known as N-type Semiconductor.22. What is doping?Process of adding impurity to a intrinsic semiconductor atom is doping. The impurity is calleddopant.

23. Which charge carriers is majority and minority carrier in N-type

Semiconductor?

majority carrier: electron and minority carrier: holes.

24.which charge carriers is majority and minority carrier in P-type

Semiconductor?

Majority carrier: holes and minority carrier: electron

25. 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.

26. 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.

27. Give the relation for concentration of holes in the n- type material?

pn = ni

2 /NDWhere

pn - concentration of holes in the n type semiconductor

ND - concentration of donor atoms in the n type semiconductor

28. Give the relation for concentration of electrons in the p - type material?

np = ni

2 /NA

Wherenp - concentration of electrons in p- type semiconductor

ND - concentration of acceptor atoms in the p type semiconductor

29. Define drift current?

When an electric field is applied across the semiconductor, the holes move towards the negative

terminal of the battery and electron move towards the positive terminal of the battery. This drift

movement of charge carriers will result in a current termed as drift current.

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30. Give the expression for drift current density due to electron.

Jn = q n nE

Where,Jn - drift current density due to electron

q- Charge of electron

n - Mobility of electronE - applied electric field

31. Give the expression for drift current density due to holes.

Jp = q p p EWhere, Jn - drift current density due to holes q - Charge of holes

p - Mobility of holes E - applied electric field

32. Define the term diffusion current?

A concentration gradient exists, if the number of either electrons or holes is greater in one region of a

semiconductor as compared to the rest of the region. The holes and electron tend to move from

region of higher concentration to the region of lower concentration. This process in called diffusion

and the current produced due this movement is diffusion current.

33. Define mean life time of a hole or and electron.The electron hole pair created due to thermal agitation woll disappear as a result of recombination.Thus an average time for which a hole or an electron exist before recombination can be said as themean life time of a hole or electron.

34. What is the other name of continuity equation? What does it indicate?

The other name of continuity equation is equation of conservation of charge.This equation indicates that the rate at which holes are generated thermally just equals the rate at

which holes are lost because of recombination under equilibrium conditions.

35. Define Hall effect?

If a metal or semiconductor carrying current I is placed in a transverse magnetic field B , an electricfield E is induced in the direction perpendicular to both I and B This phenomenon is known as Hall

effect.

36. Give some application of Hall Effect.

i). Hall Effect can be used to measure the strength of a magnetic field in terms of electrical voltage.

ii).It is used to determine whether the semiconductor is p type or n- type material

iii).It is used to determine the carrier concentrationiv).It is used to determine the mobility.

37. Define the term transition capacitance?

When a PN junction is reverse biased, the depletion layer acts like a dielectric material while P andN 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 = A / WWhere

CT - transition capacitance

A - Cross section area of the junctionW Width of the depletion region

38. What is a varactor diode?

A diode which is based on the voltage variable capacitance of the reverse biased p-n junction is saidto be varactor diode. It has other names such as varicaps, voltacaps.

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39. Define the term diffusion capacitance.

The diffusion capacitance of a forward biased diode is defined as the rate of change of injected

charge with voltage.CD = I / VT

Where, Cd time constant

I current across the diodevT threshold voltage

40. what is recovery time? Give its types.

When a diode has its state changed from one type of bias to other a transient accompanies the dioderesponse, i.e., the diode reaches steady state only after an interval of time tr called as recovery

time. The recovery time can be divided in to two types such as

(i) forward recovery time(ii) reverse recovery time

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41. What is meant by forward recovery time?

The forward recovery time may be defined as the time interval from the instant of 10% diode voltage

to the instant this voltage reaches 90% of the final value. It is represented as t f r.

42. What is meant by reverse recovery time?

The reverse recovery time can be defined as the time required for injected or the excess minoritycarrier density reduced to zero , when external voltage is suddenly reversed.

43. Define storage time.

The interval time for the stored minority charge to become zero is called storage time. It is

represented as t s.

44. Define transition time.

The time when the diode has normally recovered and the diode reverse current reaches reverse

saturaton current I0 is called as transition time. It is represented as t t

45. What are break down diodes?Diodes which are designed with adequate power dissipation capabilities to operate in the break down

region are called as break down or zener diodes.

46. What is break down? What are its types?

When the reverse voltage across the pn junction is increased rapidly at a voltage the junction breaksdown 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

47. What is zener breakdown?

Zener break down takes place when both sides of the junction are very heavily doped andConsequently 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 freecharge carriers are produced which constitute the zener current. This process is known as zener

break down.

48. 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 potentialand 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 heavyflow of current is termed as avalanche break down.

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49. How does the avalanche breakdown voltage vary with temperature?

In lightly doped diode an increase in temperature increases the probability of collision of electronsand 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.

50. 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

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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.

UNIT IV

TRANSISTORS

51. What is a transistor (BJT)?Transistor is a three terminal device whose output current, voltage and /or power

is controlled by input current.

52. What are the terminals present in a transistor?Three terminals: emitter, base, collector.

53. What is FET?FET is abbreviated for field effect transistor. It is a three terminal device with its output

characteristics controlled by input voltage.

54. Why FET is called voltage controlled device?The output characteristics of FET is controlled by its input voltage thus it is voltage controlled.

55. What are the two main types of FET?1. JFET 2. MOSFET.

56. What are the terminals available in FET?

1). Drain, 2).Source and 3). Gate

57. What is JFET?JFET- Junction Field Effect Transistor.

58. What are the types of JFET?

N- Channel JFET and P- Channel JFET

59. What are the two important characteristics of JFET?

1. Drain characteristics 2. Transfer characteristics.

60. What is transconductance in JFET?It is the ratio of small change in drain current to the corresponding change in drain to source voltage.

61. What is amplification factor in JFET?It is the ratio of small change in drain to source voltage to the corresponding change in Gate tosource voltage.

62. Why do we choose q point at the center of the loadline?

The operating point of a transistor is kept fixed usually at the center of the active region in order thatthe input signal is well amplified. If the point is fixed in the saturation region or the cut off region the

positive and negative half cycle gets clipped off respectively.

63. List out the different types of biasing. ._

Voltage divider bias, Base bias, Emitter feed back bias, Collector feedback bias, Emitter bias.

64. What do you meant by thermal runway?Due to the self heating at the collector junction, the collector current rises. This causes damage to the

device. This phenomenon is called thermal runway.

65. Why is the transistor called a current controlled device?

The output characteristics of the transistor depend on the input current. So thtransistor is called a

current controlled device.

66. Define current amplification factor?

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It is defined as the ratio of change in output current to the change in input current at constant.

67. What are the requirements for biasing circuits?

The q point must be taken at the Centre of the active region of the output characteristics. Stabilize the collector current against the temperature variations.

Make the q point independent of the transistor parameters.

When the transistor is replaced, it must be of same type.68. When does a transistor act as a switch?The transistor acts as a switch when it is operated at either cutoff region or saturation region

69. What is biasing?To use the transistor in any application it is necessary to provide sufficient voltage and current to

operate the transistor. This is called biasing.

70. What is stability factor?

Stability factor is defined as the rate of change of collector current with respect to the rate of change

of reverse saturation current.

71. Explain about the various regions in a transistor?

The three regions are active region saturation region cutoff region.

72. Explain about the characteristics of a transistor?Input characteristics: it is drawn between input voltage & input current while keeping output voltage

as constant. Output characteristics: It is drawn between the output voltage &output current whilekeeping input current as constant.

16 marks-Hints

73. Explain the construction, operation, volt ampere characteristics, and application

of SCR, also explain its two transistor model.

Maximum mark for this question: 16 marks

Construction (2marks)

Equivalent circuit and two transistor model (2marks)Operation (4marks)

Volt ampere characteristics (4marks)

Application (2marks)

74. Explain the construction, operation, equivalent circuit, volt ampere

characteristics, and application of UJT.

Maximum mark for this question: 16 marksConstruction (4marks)

Equivalent circuit (2marks)

Operation (4marks)Volt ampere characteristics (4marks)



characteristics, and application of DIAC.



Equivalent circuit (2marks)Operation (4marks)

Volt ampere characteristics (4marks)



characteristics, and application of TRIAC


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Equivalent circuit (2marks)

Operation (4marks)Volt ampere characteristics (4marks)


UNIT V

SPECIAL SEMICONDUCTOR DEVICES

78. 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 SCRs connected in antiparallel

79. Give the application of TRIAC.

1. Heater control2. Motor speed control

3. Phase control

4. Static switches

80. What are the different operating modes of TRIAC?

1. Keeping MT2 and G positive

2. Keeping MT2 and G negative.3. Keeping MT2 positive and G negative.

4. Keeping MT2 negative and G positive.

81. What are the regions in the VI characteristics of UJT?

1. Cut-off region

2. Negative resistance region.

3. Saturation region

82. 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. Thistakes place until the valley point is reached. This region between the peak point and valley point is

called negative resistance region.

83. Mention the applications of UJT.

1. It is used in timing circuits

2. It is used in switching circuits

3. It is used in phase control circuits

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4. It can be used as trigger device for SCR and triac.

5. It is used in saw tooth generator.

6. It is used for pulse generation.

84. What is a DIAC?

DIAC is a two terminal bidirectional semiconductor switching device. . It can conduct in either

direction depending upon the polarity of the voltage applied across its main terminals. In operationDIAC is equivalent to two 4 layer diodes connected in antiparallel.

85. Give some applications of DIAC.

1. To trigger TRIAC2. Motor speed control

3. Heat control

4. Light dimmer circuits

87. 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.

88. 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.

89.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.

90. How turning on of SCR is done?

1. By increasing the voltage across SCR above forward break over voltage.

2. By applying a small positive voltage at gate.

3. By rapidly increasing the anode to cathode voltage.4. By irradiating SCR with light.

91. How turning off of SCR is done?

1. By reversing the polarity of anode to cathode voltage.2. By reducing the current through the SCR below holding current.

3.By interrupting anode current by means of momentarily series or parallel switching

92. Define holding current in a SCR.

Holding current is defined as the minimum value of anode current to keep the SCR ON.

93. List the advantages of SCR.

1. SCR can handle and control large currents.2. Its switching speed is very high

3. It has no moving parts, therefore it gives noiseless operation.

4. Its operating efficiency is high.

94. List the application of SCR.

1. It can be used as a speed controller in DC and AC motors.

2. It can be used as an inverter.

3. It can be used as a converter4. It is used in battery chargers.

5. It is used for phase control and heater control.

6. It is used in light dimming control circuits.

95. What is meant by latching.

The ability of SCR to remain conducting even when the gate signal is removed is called as latching.

96. Define forward current rating of a SCR.

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Forward current rating of a SCR is the maximum anode current that it can handle without

destruction.

97. List the important ratings of SCR.

1. Forward break over voltage

2. Holding current

3. Gate trigger current4. Average forward current

5. Reverse break down voltage.

98. Compare SCR with TRIAC.

SCR TRIAC

1. unidirectional current 1. bidirectional current

2. triggered by positive pulse at gate 2. triggered by pulse of positive or negativeat gate

3. fast turn off time 3,. Longer turn off time

4. large current ratings 4. lower current ratings

99. Differentiate BJT and UJT.

BJT UJT1. It has two PN junctions 1. It has only one PN junctions

2. three terminals present 2. three terminals present are emitter,are emitter, base,collector base1,base2

3. basically a amplifying device 3. basically a switching device

100. 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.

101. What is a thyristor?

Thyristor is a semiconductor device having three or more junctions .Such a device acts as a switchwithout any bias and can be fabricated to have voltage ratings of severalhundred volts and current

ratings from a few amperes to almost thousand amperes.

102. What are the types of thyristors?

1. Unidirectional thyristors2. Bidirectional thyristors

3. Low-power thyristors

103. Give the various triggering devices for thyristors.

1. SCR2. UJT

3. DIAC

4. TRIAC

104. what is backward diode?

The backward diode is a diode in which the doping level is moderate. The forward current in this

case is very small, very much similar to that of the reverse current in the conventional diode.

105. what is a photo diode?

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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.

106. What is a LED?

A PN junction diode which emits light when forward biased is known as Light emitting diode

(LED).107. What is a tunnel diode?The tunnel diode is a pn junction diode in which the impurity concentration is greatly increased

about 1000 times higher than a conventional PN junction diode thus yielding a very thin depletionlayer. This diode utilizes a phenomenon called tunneling and hence the diode is referred as tunnel

diode.

108. What is tunneling phenomenon?

The phenomenon of penetration of the charge carriers directly though the potential barrier instead of

climbing over it is called as tunneling.

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UNIT I

1. State and explain Thevenin, Norton ,Super position, Maximum power transfer2. Problems using Thevenin, Norton ,Super position, Maximum power transfer3. Problems in KCL (Kirchoff voltage law) and KVL (Kirchoff current law)

UNIT II

1. RL, RC,RLC transient response when excited by AC & DC Source. ( see problems also)2. Frequency response of RL,RC,RLC (see problems also)3. Parallel and Series resonance4. Single tuned and double tuned circuits.

UNIT III

1. Derive the PN diode current equation?2. Draw the zener diode characteristics and explain the working of zener diode.3. Draw the zener regulation circuit and explain its function for input regulation and output regulation.4. with sufficient equation and necessary diagram explain the space charge and diffusion capacitance5. derive the expression for space charge and diffusion capacitance in step graded and linear graded.6. with neat energy band structure derive expression for open circuited PN junction.7. derive expression for carrier concentration in intrinsic semiconductor.8. Explain the classification of semiconductors.9. Explain the Theory of PN junction diode with its characteristic curve.

UNIT IV

1. What is mosfet explain the construction and working principle of enhancement mode and depletionmode mosfet.

2. Explain the operation of N channel and P channel JFET.3. Explain the characteristics of CE, CB, and CC configuration.4. Explain the types of configuration.5. Explain the operation of NPN and PNP transistor.6. Derive the expression for saturation drain current.7. Compare transistor configurations (CE,CB,CC)

UNIT V

1. Describe the working of silicon controlled rectifier with its characteristic curve.2. Explain how silicon controlled rectifier can be realized using two transistor model.3. Explain the working principle and characteristics of tunnel diode.4. Describe the principle and operation of LCD& LED.5. With necessary diagram explain the operation of UJT.6. Explain the working principle of Photodiode.7. Explain the working principle of photo transistor.8. Explain the working principle of Photo conductive cell.9. Explain the working principle of laser.10.Explain the working principle of DIAC and TRIAC.11.Explain the working principle of CCD.

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