div-a.weebly.comdiv-a.weebly.com/uploads/2/2/6/9/22691584/unit_iv.docx · Web viewA diode is a...

SEMICONDUCTOR PHYSICS

Q.1) Electrical conductivity in between conductors & insulators is 1a) high conductors b) low conductorsc) Semiconductors d) partial conductors

Q.4) The main distinction between conductors, semiconductors & insulators is Concerned with 1 a) Binding energy of electrons b) Work function c) Temperature coefficient of resistance d) Width of forbidden band

Q.5) Why metals are good conductors of heat than insulators because 1 a) They contain free electrons b) Their atoms are relative far apart c) Their atoms collide frequently d) They have reflecting surface

Q.6) If n-p-n transistor is used as an amplifier, then 1 a) Electrons move from base to collector b) Holes move from base to collector c) Electrons move from collector to base d) Holes move from collector to baseQ.8) Diamond acts as an 1 a) Conductor b) Insulator c) Semiconductor d) None of the above

Q.9) The width of the -----------------------is an important factor in determining whether the materials are conductors, semiconductors & Insulators. 1 a) Valence band b) conduction band c) Forbidden band d) band energy

Q.10) The resistivity of semiconductor varies from 1 a) 10-12 to 109Ωcm b) 10-14 to 108Ωcm c) 10-10 to 108Ωcm d) 10-15 to 10-20Ωcm

Q.11) The extrinsic semiconductor formed by doping a ----------- 2 Impurity is called an ----------- semiconductor a) Trivalent, intrinsic

b) Pentavalent, extrinsic c) Doner, p type d) Acceptor type

Q.12) The drift velocity of the electrons depends upon 1 a) electron mobility b) electron density c) Drift velocity d) electron charge

Q.13) For an N-type semiconductor, the Hall coefficient is 1 a) Negative b) positive c) One d) zero

Q.14) In NPN transistor the arrow head on emitter represents that 1 The conventional current flows from a) base to collector b) base to emitter c) Emitter to collector d) emitter to base Q.15) Choose the only false statement from the following 2 a) In conductors valence & conduction band may overlap. b) Substances with energy gap of the order of 10 eV are insulators c) The resistivity of semiconductor increases with rise in temperature. d) The conductivity of semiconductor increases with rise in temperature.

Q.16) The electrical conductivity of semiconductor increases when electromagnetic Radiation of wavelength shorter than 2480 nm is incident on it. The band gap in eV for semiconductor is 2

a) 1.1eV b) 2.5eVc) 0.5eV d) 0.7eV

Q.17) In a semiconducting material the mobilities of electron & hole are µe and µh respectively which of the following is true? 1 a) µe› µh b) µe=µh

c) µh› µe d) µe›0, µh›0

Q.18) One way in which the operation of an NPN transistor differs from that of a PNP transistor is that 1 a) the emitter junction is reversed biased in NPN b) the emitter junction injects minority carriers into the base region of the PNP c) the emitter injects holes into the base of the PNP & electrons into the base region of NPN d) the emitter injects holes into the base of NPN

Q.19) NPN transistors are preferred to PNP transistors because they have 1 a) Low cost b) low Dissipation energy c) Capable of handling large power d) Electrons have high mobility than holes & hence high mobility of energy

Q.20) If the base & collector of a transistor are in forward bias, then it can not be used as 1 a) a switch b) an amplifier c) an Oscillator d) all the above

Q.21) In NPN transistor the arrow head on emitter represents that the conventional current flows from 1 a) base to emitter b) emitter to base c) emitter to collector d) base to collector

Q.22) When two semiconductors of p-type & n-type are brought in contact with each other, the P-N junction formed behaves like 1 a) an oscillator b) a condenser c) an Amplifier d) a Conductor

Q.23) On increasing the reverse voltage in a P-N junction diode the value of reverse current will 1 a) Gradually increase b) suddenly increase c) remains constant d) gradually decrease Q.24) The forbidden energy gap in an insulator is of the order of 1 a) 1 MeV b) 0.1 MeV c) 4 MeV d) 5 MeV

Q.25) In an N-type semiconductor, doner valence band is 1 a) above the conduction band of the host crystal. b) close to the valence band of the host crystal. C) close to the conduction band of the host crystal. d) below to the valence band of the host crystalQ.28) Semiconductor devices are 1 a) temperature dependant. b) voltage dependant. c) current dependant. d) none of these.

Q.29) Which of the following properties can be different along different directions in a crystalline solids? 1

a)Electrical conductivity b) Refractive indexc) Mechanical strength. d) All of these.

Q.32) Which of the following when added as an impurity into the silicon produces n-type semiconductor?

a) P b) Alc)B d) Mg

Q.33) At OoK, intrinsic semiconductor behaves as 1 a) a perfect conductor b) a super conductor c) a semiconductor d) a perfect insulator

Q.34) In ne & nh are the number of electrons & holes in a semiconductor heavily doped with phosphorus, then 1

a) ne>>nh b) ne<<nh

c) ne<nh d) ne=nh

Q.36) An n type & p type silicon can be obtained by doping pure silicon with 1 a) Arsenic & Phosphrous b) Indium & Aluminium c) Phosphrous & Indium d) Aluminium & Boron

Q.39) In forward bias, the width of potential barrier in a p-n junction diode 1 a) increases b) decreases c) remains constant d) first (a) then (b)

Q.40) Deplection layer consists of 1 a) electrons b) protons c) mobile ions d) immobile ions

Q.41) The major constituent of transistor are 1 a) salts b) transistor c) conductors d) semiconductors

44) On reverse biasing the P-N junction,its potential barrier becomes 1 a) narrow b) broad c) zero d) constant

Q.47) The ratio of maximum useful power to ideal power is called as 1 a) Efficiency b) Open-circuit c) Fill factor d) short-circuit

Q.48) Photoelectric cells convert light energy into 1 a) solar energy b) mechanical energy c) electrical energy d) kinetic energy

Q.49) The Fermi level in intrinsic semiconductor lies exactly at the -------- 1 of the forbidden band. a) above b) below c) middle d) none of these

Q.50) In the P-type semiconductor, the hole concentration in valence band 1 Is ---------- than the electron concentration in conduction band. a) Less b) equal to c) Greater d) all of these

Q.51 ) Barrier potential of a p-n junction diode does not depend on -------1

a) temperature b)forward bias c) doping density d) diode design

Q.52 ) Reverse bias applied on a junction diode-------1

a) raises the potential barrier b) increases the majority carrier current c) increase the minority

carrier current d) lowers the potential barrier

Q.55) A semiconductor is characterized by ------- 1

a) completely filled V.B. b) partially filled C.B. c) overlapping between V.B. and C.B. d) none of

these

Q.56)In a PN junction diode --------1

a) high potential at N side and low potential at P side b) high potential at P side and low potential at

N side c) P and N both are at same potential d) undetermined.

Q.57) Which is the correct relation for forbidden energy cap in conductor, semi-conductor and insulator? 1

a) ∆Egc > ∆Egssc > ∆Eginsulator b) ∆Eginsulator > ∆ Egssc > ∆Egconductor c) ∆Egconductor > ∆Eginsulator > ∆ Egssc

d) ∆ Egssc > ∆ Egconductor > ∆Eginsulator

Q.58) When the temperature of n- type semiconductor is increases ------1

a) net negative charge is increased b) net charge is zero c) minority carriers are decreased d)none of

the above is true

Sr. No.

MCQ Questions Remarks

3 The impurity level in an extrinsic semiconductor is about_____________of pure semiconductor. 1

A)10 atoms for 108 atoms

B) 1 atoms for 108 atoms

C) 10 atoms for 104 atoms

D) 1 atoms for 100 atoms

4 In a semiconductor, current conduction is due 1 C

A) to only holes

B) to only free electrons

C) to both holes and free electrons

D) none of the above

5 The battery connection required to forward bias a p-n junction are 1 A

A) +ve terminal to p and –ve terminal to n

B) -ve terminal to p and +ve terminal to n

C) -ve terminal to p and –ve terminal to n


6 The barrier voltage of a pn junction for germanium is about 1 D

A) 1.1V

B) 3V

C) 0

D) 0.3V

9 When the crystal diode current is large, the bias is 1 A

A) forward

B)inverse

C)poor

D)reverse

11 A zener diode is always _________connected. 1 B

A) forward

B)reverse

C)either forward/ reverse


15 A semiconductor has ___________temperature coefficient of resistance. 1

C

A) positive

B)0

C)negative


16 When a pure semiconductor is heated, It’s resistance 1 B

A) goes up

B) goes down

C) remains the same

D) can not say

18 At T=0°K, all energy states below EF (i.e. E<EF) have a probability of occupancy is 1

B

A) zero

B)unity

C)1/2


19 At T=0°K, all energy states above EF (i.e. E>EF) have a probability of occupancy is 1

A

A) zero

B)unity

C)1/2


20 At T>0°K and E= EF , probability of occupancy is 1 C

A) zero

B)unity

C)1/2


21 The resistivity of the n-type semiconductor is 10-6 Ω cm. The number of donor atoms which must be added to obtain the resistivity are 2

A

A) 6.2*1021 atoms

B) 6.2*1020 atoms

C) 7*1020 atoms

D) 7*1021atoms

22 Calculate the conductivity of pure Si at room temperature when the concentration of carrier is 1.5*1016/m3 and mobilities of electrons and holes are 0.12 and 0.05 m2/V 2

A

A) 4.1*10-4 mho/m

B) 4.1*10-4 mho/cm

C) 4.1*10-5 mho/m

D) 4.1*10-5 mho/cm

23 Fermi level in an intrinsic semiconductor lies 1 C

A) nearer to valence band

B) nearer to conduction band

C)at the middle of the band gap


24 In N type semiconductor Fermi level 1 B

A) is at the middle of band gap

B) gets shifted towards the conduction band

C) gets shifted towards the valence band


25 In P type semiconductor Fermi level 1 C

A) is at the middle of band gap

B) gets shifted towards the conduction band

C) gets shifted towards the valence band


26 N type semiconductor is 1 C

A) –Vely charged

B) +Vely charged

C) electrically neutral


27 Silicon is 1 C

A) Trivalent

B) Pentavalent

C)Tetravalent


28 In case of solar cell, the conversion efficiency 1 A

A) decreases with increasing temperature

B) increases with increasing temperature

C) decreases with decreasing temperature

D) increases with decreasing temperature

29 In case of solar cell,open circuit voltage 1 A

A)decreases with increasing temperature

B) increases with increasing temperature

C) decreases with decreasing temperature

D) increases with decreasing temperature

30 The Fill Factor of the solar cell is defined as 1 D

A) Fill Factor =(Isc*Voc) /( Im* Vm)

B) Fill Factor =(Isc*Voc)

C) Fill Factor =( Im* Vm)

D) Fill Factor =( Im* Vm)/(Isc*Voc)

38 A diode is a non-linear device due to the fact that 1 B

A)It has a symmetrical anode and cathode terminal

B) Its I-V characteristic is non-linear

C) Its anode an cathode are of different material

D) None of these

39 A hole in a semiconductor is defined as C

A) a free electron

B) a free proton

C) the incomplete part of an electron pair bond

D) a free neutron

40 As the doping to a pure semiconductor increases, the bulk resistance of the semiconductor 1

C

A) remains the same

B) increases

C) decreases

D)None of these

41 A hole and electron in close proximity woul tend to 1 B

A) repel each other

B) attract each other

C) have no effect on each other

D) None of these

43 In the depletion region of pn junction, there is a shortage of 1 B

A) acceptor ions

B) holes and electrons

C) donor ions

D) None of the above

44 A reverse biased pn junction has 1 B

A) very narrow depletion layer

B) almost no current

C) very low resistance

D) large current flow

45 A pn junction acts as a 1 C

A) controlled switch

B) bidirectional switch

C) unidirectional switch


47 At room temperature, an intrinsic semiconductor has 1 B

A) many holes only

B) a few electrons and holes

C) many free electrons only

D) no holes or free electrons

48 At absolute temperature, an intrinsic semiconductor has 1

A) many holes only D

B) a few electrons an holes

C) many free electrons only

D) no holes or free electrons

49 At room temperature, an intrinsic silicon crystal acts approximately as 1

C

A) a battery

B) a conductor

C) an insulator

D) a piece of copper wire

54 A ____ is created when an electron moves from the valence band to the conduction band. 1

A

A)Hole

B) Gap

C) Vacancy

D) Blank

55 Which of the following statement is not true 1 C

A) The resistance of intrinsic semiconductors decreases with increase of temperature

B) Doping pure Si with trivalent impurities gives p-type semiconductors.

C) The majority carriers in p-tye semiconductors are holes.

D) A p-n junction can act as a semiconductor diode

56 What causes the depletion region? 1 B

A)Doping

B)Diffusion

C)barrier potential

D)Ions

57 What is an energy gap? 1 A

A)the space between two orbital shells

B)the energy equal to the energy acquired by an electron passing a 1 V electric field

C)the energy band in which electrons can move freely

D)an energy level at which an electron can exist

59 In "n" type material, majority carriers would be: 1 D

A) A)Holes

B) B)Dopants

C) Slower

D) Electrons

60 Elements with 1, 2, or 3 valence electrons usually make excellent: 1 A

A)Conductors

B)Semiconductors

C)Insulators

D)Neutral

A

61 A commonly used pentavalent material is: 1

A)Arsenic

B)Boron

C)Gallium

D)Neon

62 Which material may also be considered a semiconductor element? 1 A

A)Carbon

B)Ceramic

C)Mica

D)Argons

67 Electrons in the outermost orbit or shell of an atom are called 1 C

A)free electrons

B)negative ions

C)valence electrons

D)conduction band electrons

68 A pn junction allows current flow when 1 A

A)the p-type material is more positive than the n-type material

B)the n-type material is more positive than the p-type material

C)both the n-type and p-type materials have the same potential

D)there is no potential on the n-type or p-type materials

70 Intrinsic semiconductor material is characterized by a valence shell of how many electrons? 1

C

A)1

B)2

C)4

D)6

71 Ionization within a P-N junction causes a layer on each side of the barrier called the: 1

B

A)Junction

B)depletion region

C)barrier voltage

D)forward voltage

72 When a diode is forward biased, the voltage across it 1 D

A)is directly proportional to the current

B)is inversely proportional to the current

C)is directly proportional to the source voltage

D)remains approximately the same

A

73 Why is heat produced in a diode? 1

A)due to current passing through the diode

B)due to voltage across the diode

C)due to the power rating of the diode

D)due to the PN junction of the diode

78 Which of the following cannot actually move? 1 C

A)majority carriers

B)Ions

C)Holes

D)free electrons

79 What electrical characteristic of intrinsic semiconductor material is controlled by the addition of impurities? 1

A

A)Conductivity

B)Resistance

C)Power

D)all of the above

80 In "p" type material, minority carriers would be: 1 D

A)Holes

B)Dopants

C)Slower

D)Electrons

82 The conduction band is closest to the valence band in 1 B

A) Semiconductors

B) Conductors

C) Insulators

D) The distance is the same for all of the above.

85 How many valence electrons are in every semiconductor material? 1 D

A) 1

B) 2

C) 3

D) 4

87 Minority carriers are many times activated by: 1 A

A) Heat

B) Pressure

C) Dopants

D) forward bias

88 If conductance increases as temperature increases, this is known as a: 1 C

A) positive coefficient

B) negative current flow

C) negative coefficient

D) positive resistance

91 The voltage where current may start to flow in a reverse-biased pn junction is called the 1

A

A) breakdown voltage

B) barrier potential

C) forward voltage

D) biasing voltage

92 When transistors are used in digital circuits they usually operate in the: 1

C

A) active region

B) breakdown region

C) saturation and cutoff regions

D) linear region

94 In the middle of the depletion layer of a reverse biased p-n junction, the 1

A

A) Potential is zero

B) Electric field is zero

C) Potential is maximum

D) Electric field is maximum

95 In a p-n junction, the depletion layer consists of 1 D

A) Electrons

B) Protons

C) Mobile ions

D) immobile ions

96 Hall effect cannot explain 1 D

A)The sign of the current carrying charges

B)The number of charge carriers per unit volume

C) Direct measurement of mobility

D) The direction of electrical current

97 When a p-n junction diode is forward biased, then 1 C

A) the depletion region is reduced and barrier height is increased

B) the depletion region is widened and barrier height is reduced

C) both the depletion region is reduced and barrier height are reduced

D) both the depletion region is reduced and barrier height are increased

98 The difference in the variation of resistance with temperature in a metal and a semiconductor arises essentially due to the difference in 1

D

A) Type of bonding

B) Crystal structure

C) Scattering mechanism with temperature

D) No. of charge carriers with temperature

102

The area at the junction of p-type and n-type materials that has lost its majority carriers is called the 1

B

A) barrier potential

B) depletion region

C) n region

D) p region

104

At any given time in an intrinsic piece of semiconductor material at room temperature 1

D

A) electrons drift randomly

B) recombination occurs

C) holes are created

D) All of the above

111

An electron can move to another atom's orbit only while in the _______. 1

B

A) valence band

B) conduction band

C) orbit nearest the nucleus

D) covalent band

A

112

___ occurs when a pn junction is first formed. 1

A) Recombination

B) Covalent bonding

C) Crystallization

D) Breakdown

114 A silicon sample is uniformly doped with 1016 phosphorus atoms/cm3

and 2 × 1016 boron atoms/cm3. If all the dopants are fully ionized, the material is: 2

B

A) n-type with carrier concentration of 3 × 1016/cm3

B) p-type with carrier concentration of 1016/cm3

C) p-type with carrier concentration of 4 × 1016/cm3

D) Intrinsic

115

n-type semiconductors are: 1 C

A) Negatively charged

B) Produced when Indium is added as an impurity to Germanium

C) Produced when phosphorous is added as an impurity to silicon


116

The probability that an electron in a metal occupies the Fermi-level, at any temperature (>0 K) is: 1

C

A) 0

B) 1

C) 0.5


117

Measurement of Hall coefficient enables the determination of: 1 B

A) Mobility of charge carriers

B) Type of conductivity and concentration of charge carriers

C) Temperature coefficient and thermal conductivity


119

The conductivity of an intrinsic semiconductor is given by (symbols have the usual meanings): 1

C

A) σi = eni2 (µn – µp)

B) σi = eni (µn – µp)

C) σi = eni (µn + µp)

D) None of the above.

121

In an intrinsic semiconductor, the mobility of electrons in the conduction band is: 1

C

A) Less than the mobility of holes in the valence band

B) Zero

C) Greater than the mobility of holes in the valence band


122

The Hall coefficient of sample (A) of a semiconductor is measured at room temperature. The Hall coefficient of (A) at room temperature is 4×10–4 m3 coulomb–1. The carrier concentration in sample A at room temperature is: 2

C

A) ~ 1021 m–3

B) ~ 1020 m–3

C) ~ 1022 m–3


123

If the drift velocity of holes under a field gradient of 100v/m is 5m/s, the mobility (in the same SI units) is 2

A

A) 0.05

B) 0.55

C) 500


124 The Hall Effect voltage in intrinsic silicon is: 1 C

A) Positive

B) Zero

C) Negative


125

The Hall coefficient of an intrinsic semiconductor is: 1 B

A) Positive under all conditions

B) Negative under all conditions

C) Zero under all conditions


129 If the temperature of an extrinsic semiconductor is increased so that

the intrinsic carrier concentration is doubled, then: 1

C

A) The majority carrier density doubles

B) The minority carrier density doubles

C) Both majority and minority carrier densities double


130

At room temperature, the current in an intrinsic semiconductor is due to 1

C

A) Holes

B) Electrons

C) Holes and electrons


131 The mobility is given by (notations have their usual meaning): 1

A

A) µ = V0/E0

B) µ = V02/E0

C) µ = V0/E02


132

Hall effect is observed in a specimen when it (metal or a semiconductor) is carrying current and is placed in a magnetic field. The resultant electric field inside the specimen will be in: 1

A

A) A direction normal to both current and magnetic field

B) The direction of current

C) A direction anti parallel to magnetic field


134

A sample of n-type semiconductor has electron density of 6.25 x 1018/cm3 at 300K. If the intrinsic concentration of carriers in this sample is 2.5 x 1013/cm3, at this temperature, the hole density becomes: 2

B

A) 1016/cm3

B) 107/cm3

C) 1017/cm3


135

The intrinsic carrier density at 300K is 1.5 x 1010/cm3 in silicon. For n-type silicon doped to 2.25 x 1015 atoms/cm3, the equilibrium electron and hole densities are: 2

D

A) n0 = 1.5 x 1016/cm3, p0 = 1.5 x 1012/cm3

B) n0 = 1.5 x 1010/cm3, p0 = 2.25 x 1015/cm3

C) n0 = 2.25 x 1017/cm3, p0 = 1.0 x 1014/cm3


138

Measurement of Hall coefficient in a semiconductor provides information on the: 1

D

A) Sign and mass of charge carriers

B) Mass and concentration of charge carriers

C) Sign of charge carriers alone

D) Sign and concentration of charge carriers

141

Which of the following doping will produce a p-type semiconductor 1 D

A) Germanium with phosphorus

B) Silicon with Germanium

C) Germanium with Antimony

D) Silicon with Indium

144

Current in a Metal is due to______________ 1 C

A) Protons

B) neutrons

C) electrons

D) holes

145

Flow of Current in a semi conductor is due to__________ D

A) Protons

B) electrons

C) Holes

D) both C & B

14 Currrent Produced in a metal when constant Electric field is applied is D

6 _________ 1

A) pure Currrent

B) impure Current c

C) Diffusion Current

D) Drift Current

148

At Higher Energies Number Of Forbidden Energy Levels in a Metal_______ 1

B

A) 1

B) 0

C) 2

D) infinite

149

Energy gap of semi conductors is Expressed in(units)__________ 1 D

A) joules

B) coulombs

C) ergs

D) electron volts

150

Energy Gap of conductors is _____________1 A

A) 0 eV

B) 1 eV

C) infinite

D) -1 eV

151

Conductivity of Intrinsic semi conductors depend up on _________1 A

A) Temperature

B) band Gap

C) both A and B

D) None of these

152

Resistance of Semiconductor___________1 B

A) Increases with temperature

B) decreases with temperature

C) independent of temperature

D) none

153

Which of the following statement is not true 1 C

When a potential difference is applied across, the current passing through

A) an insulator at 0 K is zero

B) a semiconductor at 0 K is zero

C) an metal at 0 K is finite

D) a p-n diode at 300 K is finite if it is reverse biased

154

The probability of an electron occupying an energy level below Fermi level is 1

B

A) 0%

B) 100%

C) 50%

D) 30%

155

The probability of an electron occupying an energy level above Fermi level is 1

A

A) 0%

B) 100%

C) 50%

D) 30%

156

Fermi-Dirac statistics deal with particles of spin 1 B

A) 0

B) 1/2

C) 1

D) 2

158

In a metal, if the temperature is increased then resistivity 1 A

A) increases

B) decreases

C) remains same

D) none of these

161

A small concentration of minority carriers is injected into a homogeneous semiconductor crystal at one point. An electric field of 10 V.cm is applied across the crystal and this moves the minority carriers a distance of 1 cm is 20 µsec. The mobility (in cm2/volt.sec) is: 2

D

A) 1,000

B) 2,000

C) 50


164

The Fermi factor for E = EF at any temperature is 1 B

A) 1

B) 1/2

C) 0

D) 2

Objective questions on solid state physics 1) In semiconductors that contains donar atoms and free electron belong to the type1 a) N b) P c) hole d) None of the above 2) An N-P-N transistor can’t contain the element a) arsenic b) gallium c) indium d) calcium 3) In P-type semiconductor materials, the majority carrier’s are 1 a) positive holes b) electrons c) protons d) none of the above 4) In N-type semiconductor materials, the majority carrier’s are1 a) positive holes b) electrons c) neutrons d) proton 5) In P-N-P transistor, the collector current is a) equal to emitter current b) less than emitter current c) greater than emitter current d) none of the above 6) In N-P-N transistor, P works as a) collector b) emitter c) base d) all above 7) The distinction between conductor, insulators and semiconductor is largely concerned With1 a) their ability to conduct current b) the type of crystal lattice c) binding energy of their electronsw d) relative widths of their energy gaps 8) There is no hole current in good conductors because they 1 a) are full of electron gas b) have large forbidden gap c) have no valence band d) have overlapping valence and conduction band 9) Conduction electrons have the mobility greater than holes because they 1 a) are lighter b) have negative charge

c) need energy to move d) experience collision less frequently 10) Donar type semiconductor is formed by adding impurity of valency1 a) 3 b) 4 c) 5 d) 6 11) Acceptor type semiconductor is formed by adding impurity of valency1 a) 3 b) 4 c) 5 d) 6 13) doping materials are called impurities because they 1 a) Decrease no. of charge carrier b) Change the chemical properties of semiconductor c) Makes semiconductor impure d) Alter crystal structure of pure semiconductor 14) A piece of Cu and Ge is cooled from room temp. to 800K .the resistance of 1 a) both increases b) both decreases c) Cu increases and Ge decreases d) Cu decreases and Ge increases 18) In an intrinsic semiconductor the Fermi level lies almost 1 a) at the centre of forbidden gap b) near to conduction band c) near to valence band d) all above

21) The Fermi level in N-type semiconductor at 00K lies1 a) Below donar level b) between conduction band and donar level c) Coincides with intrinsic Fermi level d) none 22) When a free electron recombination with a hole, results 1 a) generation of energy b) release of energy c) no change in energy d) loss in energy

32) Fermi level is 1 a) lowest occupied energy level at 00K b) moderately occupied energy level at 00K c) highest occupied energy level at 00K d) all above 33) Fermi energy in intrinsic semiconductor is given by 1 a) EF = (EC- EV)/2 b) EF= (EC+EV)/2 c) EF = 2(EC- EV) d)EF = 2(EC+ EV) 34) Conductivity of conductors is given by1 a) σ = n e µe b) σ = p e µh c) σ = 1/(n e µe) d) σ = 1/(p e µh) 39) The Fermi energy is varies with temperature as 1 a) rises b) lowers c) remains unchanged d) none of above

Solid state physics

1) The group of discrete but closely spaced energy level is called …….1a) Energy band b) band c) insulator d) a intrinsic band

2) In energy band the energy levels are ………..1

a) not closely spaced b) discrete and closely spaced c) a intrinsic d) A extrinsic 3) The highest occupied energy band is ……band 1

a) extrinsic b) a intrinsic c) valance d) fully filled

4) Valance band is never ……1

a) extrinsic b) intrinsic c) valance d) empty

5) The lowest unfilled energy band is ….band1

a) conduction b) valance c) a intrinsic d) A extrinsic

6) Conduction band is always …..in insulator 1

a) valance b) empty c) Energy band d) a intrinsic

7) ……….Band is made up of series of non permitted energy level 1

a) a intrinsic b) valance c) forbidden d) Energy

8) A sample of G is transparent to radiation of wave length greater than 17760 A0 .energy gap must be …..eV. (h=6.63 X 10-34 Js,c= 3X 108 m/s)2

a) 0.87 b) 0.77 c) 0.8 d) 0.70 9) P type semiconductor is …….. 1

a) An extrinsic b) a intrinsic c) tetravalent d) pentavalent 10) N type semiconductor is …….. 1

a) tetravalent b) An extrinsic c ) a intrinsic d) trivalent 11) An intrinsic semiconductor behaves as a ….at 0 o K.1

a ) insulator b) conductor c) semiconductor d) valance 12) The conductivity of intrinsic semiconductor ……with increase in temperature. 1

a) Same b) increases c) decreases d) constant 13) Fermi level in intrinsic semiconductor lies…… of the forbidden band 1

a) Exactly middle b ) Exactly up c) Exactly down d) Exactly constant 14) In N type semiconductor, fermi level is shifted towards the ……...band.1

a) non of this b) forbidden c) conduction d) valance 15) In P type semiconductor ,fermi level is shifted towards the ……...band 1

a) non of this b) conduction band c) Energy band d) valence 16) The position of fermi level depends on ……….1

a) temperature b) pressure c) velocity d) density17) Drift velocity of electrons depends upon mobility and strength of ………1

a)non of this b) applied electric field c) applied magnetic field d) applied electromagnetic field

18) The product of electron density, charge of electron and mobility of electron is equal to …..1

a) probability b) velocity c) conductivity d) resistivity

Q.no. Ans Q.no. Ans Q.no. Ans Q.no. Ans

151 a 160 b 169 c 178 d

152 b 161 c 170 d 179 a

153 c 162 d 171 a 180 b

154 d 163 a 172 b

155 a 164 b 173 c

156 b 165 c 174 d

157 c 166 d 175 a

158 d 167 a 176 b

159 a 168 b 177 c

Semiconductor

1. In N-type semiconductor current flows due to 1

(a) Proton

(b) electrons

(e) Neutron

(d) positive ions

2. In P-type semiconductor, there are : 1

(a) no majority carriers

(b) Holes as majority carriers

(c) electron as majority carriers

(d) positive ions

4. The distinction between conductors, insulators and semiconductors is largely connected with :1

(a) their ability to conduct current ‘

(b) relative widths of their energy gaps

(c) binding energy of their electron:

(d) All above

7. The electrical conductivity of pure germanium can be increased by :1

(a) increasing the temperature

(b) doping acceptor impurities

(c) doping donor impurities

(d) All above

8. In a P-N junction with open ends :2

(a) there is constant electric field near the junction

(b) holes and conduction electrons systematically go from the P-side to the N-side and

from the N-side to the P-side respectively

(c) there is no net charge transfer between the two sides

(d) All above

10. In a semiconductor:1

(a) there are no free electrons at 0° K

(b)the number of free electrons is less than that in a conductor

(c) the number of free electrons increases with temp.

(d) All above

11. A semiconductor is doped with a donor impurity1

(a) the hole concentration increases

(b) the hole concentration is constant

(c) the electron concentration increases

(d) the electron concentration decreases

(d) a and b both correct

Answers

1. b 2. b 3. d 4. d 5. b 6. a 7. d 8. d 9. c

10. d 11 c 12. d

l. A Ge atom contains1

(a) four orbits

(b) two orbits

(c) five valence holes

(d) four valence electrons.

4. An electron in conduction band has1

(a) no charge

(b) higher energy than electron in the valance band

(c) lower energy than the electron in the valance band

(d) none of above

5. At room temperature when voltage is applied to the intrinsic semiconductor1

(a) electrons move towards the positive terminal and holes move towards the negative

terminal

(b) both holes and electrons move towards the positive terminal

(c) booth holes and electrons move towards the negative terminal

(d) none of above

8. The p-type impurities create1

(a) excess number of electrons

(b) excess number of holes

(c) excess number of ionized positive charges

(d) none of above

11. Conduction band is1

(a) the same as valance band

(b) always located at the top of the crystal

(c) is called forbidden band

(d) the energy band above forbidden band

12. Forbidden band is

(a) above conduction band

(b) below valance band

c) between valance and conduction band

(d) none of above

I3. The concentration of minority carriers in the n-type semiconductor depends on1

(a) doping technique

(b) temperature of the material

(c) quality of intrinsic Ge or Si

(d) number of donor atoms

14. A neutral semiconductor1

(a) has no free charge carrier

(b) has equal number of electrons and holes

(c) has no minority carrier

(d) has no majority carrier

15. A p-type material is1

(a) neutral

(b) negatively charged

(d) positively charged

(d) insulator

16. A n-type material has1

(a) electrons as majority carriers

(b) holes as majority carriers

(c) both positive and negative charge carriers are equal in number

(d) none of above

l9. Resistivity of semiconductor depends upon1

(a) shape and its length

(b) its carrier concentration

(c) neither shape nor carrier concentration

(d) none of above

21. The process of doping1

(a) increases conductivity

(b) decreases conductivity

(c) neither increases nor decreases conductivity

(d) none of above

25. Every time a covalent bond is broken it results in1

(a) free electron

(b) free hole

(c) electron hole pair

(d) none of above

26. Intrinsic semiconductor contains1

(a) more number of electrons

(b) more number of holes

(c) equal number of electrons and holes

(d) equal number of negative and positive immobile charges

29. Normally used semiconductor materials a are1

(a) C, Na

(b) Si, Ge

(c) GaAsP

(d) none of above

(d) none of above

35. Extrinsic semiconductor is1

(a) pure semiconductor

(b) impure semiconductor

(c) neither pure nor impure

(d) none of above

36. Conductivity of a semiconductor can be controlled by1

(a) adding impurity

(b) increasing size

(c) changing temperature

(d) none of above

38. In an intrinsic silicon the band gap is1

(a) l.l eV (b) 0.7 eV

(c) 2 eV (d) 0.2 eV

39. In an intrinsic Ge the band gap is1

(a) l.12eV (1)) 0.7 eV

(c) 0.2 eV (d) 0.6 eV

55. Mobile electrons are found in1

(a) conduction band

(b) valence band

(c) below the valence band

(d) in the band gap

56. Mobile hole are found in1

(a) conduction band

(b) valence band

(c) below the valence band

(d) in the band gap

59. The donor energy band is available in n-type material in the1

(a) conduction band

(b) valance band

(c) in the band gap

(d) none of above

60. The acceptor energy band is available in p-type material in the1

(a) band gap

(b) conduction band

(c) in the valance band

(d) none of above

71. In order to get excess electrons from the intrinsic semiconductor one can add …………to tetravalent

element1

(a) pentavalent element

(b) trivalent element

(c) tetravalent elernent

(d) none of above

72. In order to get excess holes from the intrinsic semiconductor one can add ………………..to tetravalent

element1

(a) pentavalent element

(b) trivalent element

(c) tetravalent element

(d) none of above

73. Electrons in the outermost orbit are called1

(a) valence electrons

(b) conduction electrons

(c) donor electrons

(d) none of above

77. Velocity of electron is1

(a) proportional to its mobility

(b) inversely proportional to its mobility

(c) constant

(d) none of above

78. Velocity of holes/electrons are proportional to1

(a) electric filled

(b) magnetic field

(c) inverse of magnetic field

(d) none of above

90. The conductivity of a material is expressed as1

(a) q(nµn + pµp)

(b) qA/(nµn + pµp)

(c) l/q(nµn + pµp)

(d) none of above

92. The Fermi function is expressed as1

(a) 1/ 1+exp(E-Ef)/KT

(b) 1/ 1+exp-(E-Ef)/KT

(c) exp-(E-Ef)/KT

(d) none of above

Answers

1. (d) 2. (a) 3. (a) 4. (b) 5. (a) 6. (a)

7. (a) 8. (b) 9. (c) 10. (a) 11. (d) 12 (c)

13. (b) 14. (b) 15. (a) 16. (c) 17. (a) 18. (a)

I9. (b) 20. (a) 21. (a) 22. (a) 23. (c) 24. (c)

25. (c) 26. (c) 27. (b) 28. (a) 29. (b) 30. (a)

31. (a) 32. (b) 33. (a) 34. (b) 35. (b) 36. (a)

37. (a) 38. (a) 39. (b) 40. (a) 41. (b) 42. (a)

43. (b) 44. (b) 45. (a) 46. (a) 47. (a) 48. (b)

49. (a) 50. (a) 51. (a) 52. (a) 53. (a) 54. (a)

55. (a) 56. (b) 57. (a) 58. (a) 59. (c) 60. (a)

61. (a) 62. (a) 63. (a) 64. (a) 65. (a) 66. (a)

67. (a) 68. (a) 69. (b) 70. (a) 71. (a) 72. (b)

73. (a) 74. (a) 75. (a) 76. (b) 77. (a) 78. (a)

79. (a) 80. (a) 81. (a) 82. (a) 83. (c) 84. (c)

85. (b) 86. (a) 87. (b) 88. (a) 89. (c) 90. (a)

91. (c) 92. (a) 93. (c) 94. (a) 95. (b) 96. (a)

97. (a) 98. (b) 99. (a) 100. (a) 101. (a) 102. (a)

103. (a) 104. (b) 105. (d) 106. (a) and (b) 107. (c)

Q.3 The electrical resistance of depletion layer is large because:1

[a] it has no charge carriers

[b] It has large number of charge carriers

[c] It contains electrons as charge carriers

[d] It has holes as charge carriers

Q.11 What is the conductivity of semiconductor if electron density= 5x1012/cm3 and hole density = 8x1013/cm3[μe=2.3 and μh=0.01 in SI units]2

[a] 5.634 [b] 1.968

[c] 3.421 [d] 8.964

Q.18 One serious drawback of semiconductors is1

[a] they are costly

[b] They pollute the environment

[c] They do not last for long time

[d] They can’t withstand high voltage

Q.36 A non conducting device is connected in a series circuit with battery and resistance. A current is found to pass through the circuit. If the polarity of the battery is reversed, the current drops to almost zero. The device may be1

[a] p n junction diode

[b] an intrinsic semiconductor

[c] a p type semiconductor

[d] an n type semiconductor

Q.10 Within depletion region of the pn junction diode1

[a] p side is positive and n side is negative

[b] p side is negative and n side is +ive

[c] both sides are either positive or negative

[d] both sides are neutral

Q No Question Answ

er

1 Which of the following statements correctly describes a metal within band theory?1

(a) A material possessing moderate band gap(b) A material possesses a large band gap(c) A material with zero band gap(d) A material with infinite band gap

c

2 Which is the correct ordering of the band gaps energy?1

(a) Diamond > silicon > copper(b) Diamond < silicon < copper(c) Diamond < silicon > copper(d) Diamond < silicon < copper

a

6 At 0 Kelvin, semiconductors are1

(a) Perfect metals(b) Perfect semiconductors(c) Perfect non-metals(d) Perfect insulator

d

8 Solids with high value of conductivity are called:1

(a) Conductors(b) Non-metal(c) Insulator(d) Semi conductor

a

10 At absolute zero (0 K) conduction band will be1

(a) Fully occupied by electrons(b) Completely empty(c) Partially occupied by electrons(d) Partially occupied by holes

B

12 For metals conduction band and valence band are1

(a) Fully occupied(b) Empty(c) Partially occupied(d) Overlapping

D

Q No

Question Answer

2 What happens to the Fermi energy level if a forward bias is applied to a PN junction diode?1

(a) Fermi energy level decreases for N-type while increases for P-type (b) Fermi energy level increases for N-type while decreases for P-type (c) Fermi energy levels remains in equilibrium in both regions to allow

current to flow(d) Fermi energy levels increases for both the regions

B

3 What happens to the Fermi energy level if a reverse bias is applied to a PN junction diode?1

(a) Fermi energy level decreases for N-type while increases for P-type (b) Fermi energy level increases for N-type while decreases for P-type

A

(c) Fermi energy levels remains in equilibrium in both regions to allow current to flow

(d) Fermi energy levels increases for both the regions

4 When a P-type and N-type semiconductors are joined to form a PN junction2

(a) The electrons are transferred from P-region to N-region and Fermi energy level of both regions decreases

(b) The electrons are transferred from P-region to N-region and Fermi energy level of both regions increases

(c) The electrons are transferred from N-region to P-region and Fermi energy level both regions attains equilibrium

(d) The electrons are transferred from N-region to P-region and Fermi energy level of both regions increases

C

5 In equilibrium state of a PN junction diode1

(a) Fermi energy level of P-region is higher than that of N-region(b) Fermi energy level of N-region is lower than that of P-region(c) Fermi energy levels of both the regions are at minimum value (d) Fermi energy levels of both the regions attend thermal equilibrium

D

Q No

Question Answer

4 The Fermi Function represents the probability of occupation which of the following energy level by an electron?1

a) For electrons only at Fermi energy level b) For electrons at any energy level c) For electrons only above Fermi energy level d) For electrons only below Fermi energy level

B

Q No

Question Answer

4 The Fermi Function represents the probability of occupation which of the following energy level by an electron?

e) For electrons only at Fermi energy level f) For electrons at any energy level g) For electrons only above Fermi energy level h) For electrons only below Fermi energy level

B

Q No

Question Answer

1 Hall effect is true for 1

(a) Metals only(b) Semiconductors only (c) Both metals and semiconductors (d) For N-type semiconductors only

C

2 Hall effect is true for1

(a) Both N-type and P-type semiconductors(b) N-type Semiconductors only(c) P-type Semiconductors only(d) Metals only

A

3 When current flows along the length of the semiconductor slab and magnetic field applied is perpendicular the length to Hall voltage developed is

(a) Along the length (b) Along the thickness(c) Along the width (d) Along the edges from where current enters

C

4 In Hall effect, if only the direction of the current is changed in the material

(a) The value of Hall voltage developed increases(b) The value of Hall voltage developed in opposite direction, but its value

remains constant(c) The value of Hall voltage developed decreases(d) The Hall effect do not appear

B

5 In Hall effect, if only the direction of the magnetic field applied to the material is changed

(e) The value of Hall voltage appears(f) The value of Hall voltage developed decreases(g) The value of Hall voltage developed in opposite direction, but its value

remains constant(h) The Hall effect do not appear

C

6 In Hall effect, if only the direction of the current is changed in the material the Hall electric field

(a) Hall electric field is developed in opposite direction(b) Hall electric field do not change the direction(c) Hall electric field increases(d) Hall electric field decreases

A

7 In Hall effect, if only the direction of the magnetic field is changed the Hall electric field

(a) There is no effect of Hall electric field (b) Hall electric field increases

D

(c) Hall electric field decreases(d) Hall electric field is developed in opposite direction

8 If the thickness of the material is reduced, the Hall voltage developed

(a) Decreases(b) Increases(c) Remains constant(d) Changes the direction

B

9 If the thickness of the material is increased, the Hall voltage developed


A

10 If the strength of magnetic field is increased, the Hall voltage developed

(a) Decreases(b) Remains constant(c) Increases(d) Changes the direction

C

11 If the strength of magnetic field is decreased, the Hall voltage developed


A

12 If the magnitude of current is increased, the Hall voltage developed


B

13 If the magnitude of current is decreased, the Hall voltage developed A

(e) Decreases(f) Increases(g) Remains constant(h) Changes the direction

14 If the density of charge carriers is increased, the value of Hall voltage


A

15

If the density of charge carriers is increased, the value of Hall coefficient


A

16

If the current flowing through the semiconductor slab along its length, Hall voltage and electric field developed is due to accumulation of charge carriers

(a) Along opposite edges of its thickness(b) Along opposite edges of its width(c) Along opposite edges of its length(d) Along the ends from where current enters

B

Q No Question Answer

1 The free electron theory could not explain which of the following properties?

(e) Electrical and thermal conductivity of metals(f) Thermal and thermal conductivity of non-metal(g) Ferromagnetism(h) Ohm’s law

C

2 Free electron theory is based on which of the following assumption?

(a) Electrons are freely moving only at the centre of the solid(b) Electrons behaves are freely moving through entire the solid(c) Electrons can move freely only at the top surface of the solid(d) Electrons can move freely only along the surfaces of the solid

B

3 Which statement is correct regarding the influence of temperature on conductivity?

(a) Conductivity of metals increases with increase in temperature(b) Conductivity of metals decreases with increase in temperature(c) Conductivity of semiconductors decreases with increase in temperature(d) Conductivity of semiconductors do not change with increase in temperature

B

4 When light incidents on metals what is the effect on its conductivity?

(a) Conductivity almost remain constant with only little heating

A

(b) Conductivity increases along with little heating of the material(c) Conductivity decreases along with little heating of the material(d) Conductivity decreases as electrons are emitted from the material

5 When light incidents on semiconductors what is the effect on its conductivity?

(a) Conductivity almost remain constant with little heating(b) Conductivity is not affected(c) Conductivity increases as electrons are promoted to conduction band after absorbing light(d) Conductivity decreases as electrons absorb photons and move with more random motion

D

6 What is the effect of impurity on metals?

(a) Impurity increases into increase of mobility of electrons (b) Impurity result into more scattering of electrons and conductivity decreases(c) Impurity result into more scattering of electrons and conductivity increases(d) Impurity does not affect the conductivity

B

7 Density of states function implies

(a) Number of available energy levels of electrons in unit volume per unit temperature(b) Number of available energy levels of electrons in unit volume(c) Number of available energy levels of electrons in unit volume per unit energy interval(d) Number of available electrons of per unit volume of the solid

C

8 Under the influence of external electric or magnetic field, when an electrons moves inside a solid what happens to its mass?

(a) The mass of electron is a constant quantity and it remains constant(b) The mass of electron increases due to absorption of external energy(c) The mass of electron increases or decreases depending on the potential of positive ions(d) The external field will only change the resistance, but mass of electron is not affected

C

9 What is the effect of at very high temperature on N-type semiconductors?

(a) Concentration of electrons and holes is almost equal due to ionization of donor ions and it turns into intrinsic semiconductor

(b) Concentration of electrons is more and it becomes more negative (c) More holes are created as electrons become free and it turns into P-type semiconductor(d) It turns more negative as more electrons will break the bonds and become free

A

10 What is the effect of at very high temperature on P-type semiconductors?

(a) Concentration of electrons and holes is almost equal due to ionization of donor ions and it turns into intrinsic semiconductor

(b) Concentration of holes is more and it becomes more positive(c) More electrons are created and it turns into N-type semiconductor(d) It turns more positive as more electrons will break the bonds and more holes are created

A

11 What is the effect of very high temperature on N-type semiconductors?

(a) Fermi level continue to increases as more electrons are free and conducting(b) Fermi level continue to decreases as more electrons are free creating more holes(c) Fermi level becomes equal to its intrinsic Fermi level is concentration of holes and

electrons is balanced(d) Fermi level is unbalanced and fluctuates rapidly

C

12 What is the effect of very high temperature on P-type semiconductors?

(a) Fermi level continue to increases as more electrons are free and conducting(b) Fermi level continue to decreases as more electrons are free creating more holes(c) Fermi level becomes equal to its intrinsic Fermi level is concentration of holes and

electrons is balanced(d) Fermi level is unbalanced and fluctuates rapidly

C

13 If the doping concentration of donor ions increased, what is the effect on Fermi energy of N-type semiconductor?

(a) Fermi level increase but always remain below the energy level of conduction band(b) Fermi level increases and merge into energy level of conduction band(c) Fermi level increase and goes above the energy level of conduction band(d) Fermi level is unbalanced and fluctuates rapidly

B

14 If the doping concentration of acceptor ions increased, what is the effect on Fermi energy of P-type semiconductor?

(a) Fermi level decreases but always remain above the energy level of valence band(b) Fermi level decreases and merge into energy level of valence band(c) Fermi level decreases increase and goes down the energy level of valence band(d) Fermi level is unbalanced and fluctuates rapidly

B

15 What is true regarding drift current?

(a) Drift current is caused because of unequal concentration of electrons within the solid(b) Drift current is caused because of unequal concentration of holes within the solid(c) Drift current is caused due to smooth flow of electrons within the solid(d) Drift current is caused because of random motion of electrons with ions or electrons

D

16 What is true regarding diffusion?

(a) Diffusion is caused because of random movement of electrons and holes within the solid(b) Diffusion is caused due removal of electrons in solid when power supply is connected(c) Diffusion is passing of electrons and holes through potential barrier(d) Diffusion is caused because of unbalanced distribution of concentration of electrons or

holes within the solid

D

Q No

Question Answer

1 The solar cell works

(e) Only infra-red light rays(f) Only ultra-violet light rays (g) Only visible light rays(h) for entire range of electromagnetic spectrum

D

2 If anti-reflection coating is made over the solar cell

(a) It will increase reflection of light rays and efficiency of solar cell will decrease

(b) It will increase reflection of the light rays and efficiency of solar cell will increase

(c) It will reduce the reflection of light rays and efficiency of solar cell will increase

(d) It will reduce the reflection of light rays and efficiency of solar cell will decrease

C

3 In a solar cell short circuit current refers to

(a) Maximum current when load resistance is minimum(b) Minimum current when load resistance is maximum(c) Maximum current when load resistance is maximum(d) Minimum current when load resistance is minimum

A

4 In a solar cell open circuit voltage refers to

(a) Maximum voltage when load resistance is minimum(b) Minimum voltage when load resistance is maximum(c) Maximum voltage when load resistance is maximum(d) Minimum voltage when load resistance is minimum

C

5 What is true regarding a solar cell

(a) It works only for sunlight and not for artificial light sources(b) It works only for monochromatic and coherent light(c) It works only for visible part of the spectrum (d) It works when any type of electromagnetic radiation falls over it

D

6 A solar cell converts ______

(a) heat energy into electrical energy(b) solar energy into electrical energy(c) heat energy into light energy(d) solar energy into light energy

B

7 A solar cell works on the principle of

(a) Photoelectric effect(b) Photovoltaic effect(c) Photoluminescence(d) Photo-combustion

B

8 The fill factor of a solar cell is the ratio of

(a) Actual power output to theoretical power (b) Theoretical power to actual power output(c) Actual power output to incident power(d) Theoretical power to incident power

A

9 Efficiency of a solar cell is the ratio of

(a) Actual power output to theoretical power (b) Theoretical power to actual power output(c) Actual power output to incident power(d) Theoretical power to incident power

C

10

Solar cells are usually connected in an array. Which factor gets add up due to this arrangement?

(a) total output voltage of all solar cells(b) total fill factor of all solar cells(c) total efficiency of all solar cells(d) total output current of all solar cells

D

11

To have maximize the output from solar cells

(a) an current amplifier is used to connect solar cells(b) they are connected in parallel(c) they are connected in series(d) a voltage amplifier is used to connect solar cells

C

12

If the power incident on solar cell is increased

(a) efficiency and fill factor both increases(b) efficiency and fill factor both decreases(c) efficiency increases but fill factor decreases(d) efficiency decreases but fill factor increases

A

Unit 4: Solid state PhysicsMCQ Question Bank

Q. No

Question Answer

1 When a P-type and N-type semiconductors are joined together to form a PN junction, what happens to the Fermi energy levels

(i) Fermi energy level decreases for N-type while increases for P-type until equilibrium is obtained

(j) Fermi energy level increases for N-type while decreases for P-type until equilibrium is obtained

(k) Fermi energy level remains constant but the distribution of holes and electrons changes

(l) Fermi energy level remains unchanged and equilibrium is obtained

A

2 What happens to the Fermi energy level if a forward bias is applied to a PN junction diode?

(e) Fermi energy level decreases for N-type while increases for P-type

(f) Fermi energy level increases for N-type while decreases for P-type

(g) Fermi energy levels remains in equilibrium in both regions to allow current to flow

(h) Fermi energy levels increases for both the regions

B

3 What happens to the Fermi energy level if a reverse bias is applied to a PN junction diode?

(e) Fermi energy level decreases for N-type while increases for P-type

(f) Fermi energy level increases for N-type while decreases for P-type

(g) Fermi energy levels remains in equilibrium in both regions to allow current to flow

(h) Fermi energy levels increases for both the regions

A

4 When a P-type and N-type semiconductors are joined to form a PN junction

(e) The electrons are transferred from P-region to N-region and Fermi energy level of both regions decreases

(f) The electrons are transferred from P-region to N-region and Fermi energy level of both regions increases

(g) The electrons are transferred from N-region to P-region and Fermi energy level both regions attains equilibrium

(h) The electrons are transferred from N-region to P-region and Fermi energy level of both regions increases

C

5 In equilibrium state of a PN junction diode

(e) Fermi energy level of P-region is higher than that of N-region(f) Fermi energy level of N-region is lower than that of P-region(g) Fermi energy levels of both the regions are at minimum value (h) Fermi energy levels of both the regions attend thermal

equilibrium

D

6 In an equilibrium state of an NPN transistor, what is true for Fermi energy levels

(a) (Fermi energy emitter) > (Fermi energy base) > (Fermi energy collector)

(b) (Fermi energy emitter) < (Fermi energy base) > (Fermi energy collector)

(c) (Fermi energy emitter) = (Fermi energy base) = (Fermi energy collector)

(d) (Fermi energy emitter) > (Fermi energy base) < (Fermi energy collector)

C

7 For a biased NPN transistor, what is true for Fermi energy levels

(a) (Fermi energy emitter) > (Fermi energy base) > (Fermi energy collector)

(b) (Fermi energy emitter) < (Fermi energy base) > (Fermi energy collector)

(c) (Fermi energy emitter) = (Fermi energy base) = (Fermi energy collector)

(d) (Fermi energy emitter) > (Fermi energy base) < (Fermi energy collector)

A

8 Hall effect is true for

(m) Metals only(n) Semiconductors only (o) Both metals and semiconductors (p) For N-type semiconductors only

C

9 Hall effect is true for

(e) Both N-type and P-type semiconductors(f) N-type Semiconductors only

A

(g) P-type Semiconductors only(h) Metals only

10 When current flows along the length of the semiconductor slab and magnetic field applied is perpendicular the length to Hall voltage developed is

(e) Along the length (f) Along the thickness(g) Along the width (h) Along the edges from where current enters

C

11 In Hall effect, if only the direction of the current is changed in the material

(i) The value of Hall voltage developed increases(j) The value of Hall voltage developed in opposite direction, but its

value remains constant(k) The value of Hall voltage developed decreases(l) The Hall effect do not appear

B

12 In Hall effect, if only the direction of the magnetic field applied to the material is changed

(m) The value of Hall voltage appears(n) The value of Hall voltage developed decreases(o) The value of Hall voltage developed in opposite direction, but its

value remains constant(p) The Hall effect do not appear

C

13 In Hall effect, if only the direction of the current is changed in the material the Hall electric field

(e) Hall electric field is developed in opposite direction(f) Hall electric field do not change the direction(g) Hall electric field increases(h) Hall electric field decreases

A

Q. No

Question Answer

14 If the thickness of the material is reduced, the Hall voltage developed

(e) Decreases(f) Increases(g) Remains constant

B

(h) Changes the direction15 If the thickness of the material is increased, the Hall voltage

developed


A

16 If the strength of magnetic field is increased, the Hall voltage developed

(e) Decreases(f) Remains constant(g) Increases(h) Changes the direction

C

17 If the strength of magnetic field is decreased, the Hall voltage developed


A

18 If the magnitude of current is increased, the Hall voltage developed

(i) Decreases(j) Increases(k) Remains constant(l) Changes the direction

B

19 If the magnitude of current is decreased, the Hall voltage developed

(m) Decreases(n) Increases(o) Remains constant(p) Changes the direction

A

20 If the density of charge carriers is increased, the value of Hall voltage

(e) Decreases(f) Increases

A

(g) Remains constant(h) Changes the direction

21 Which of the following statements correctly describes a metal within band theory?

(i) A material possessing moderate band gap(j) A material possesses a large band gap(k) A material with zero band gap(l) A material with infinite band gap

C

Q. No

Question Answer

22 Which is the correct ordering of the band gaps energy?

(e) Diamond > silicon > copper(f) Diamond < silicon < copper(g) Diamond < silicon > copper(h) Diamond < silicon < copper

A

23 Which statement is true regarding electrical conductivity of materials?

(a) Electrical conductivity of a metal increases with temperature(b) Electrical conductivity of a semiconductor increases with

temperature(c) Electrical conductivity of a metal decreases with temperature(d) Electrical conductivity of a semiconductor decreases with

temperature

B

24 Which statement is incorrect at ordinary room temperature?

(a) In metals electron can jump from valence band to conduction band easily

(b) In semiconductors few electrons can jump from valence band to conduction band

(c) In semiconductors is pure insulator at ordinary room temperature

(d) In insulators electrons cannot jump from valence band to conduction band

C

25 Which statement is incorrect about semiconductors?

(a) A charge carrier may be either a positive hole or an electron(b) Ga-doped Si is a p-type semiconductor(c) n- and p-type semiconductors are intrinsic semiconductors

C

(d) Doping Si with As introduces a donor level below the conduction band

26 At 0 Kelvin, semiconductors are

(e) Perfect metals(f) Perfect semiconductors(g) Perfect non-metals(h) Perfect insulator

D

27 In an intrinsic semiconductors, what is true of the following?

(a) Concentration of electrons and hole is equal(b) Concentration of electrons is greater than holes(c) Concentration of holes is greater than electrons(d) Concentration of holes and electrons vary by very small amount

A

28 Solids with high value of conductivity are called:

(e) Conductors(f) Non-metal(g) Insulator(h) Semi conductor

A

29 The electrons in valence band are

(a) Freely moving inside the solid (b) Tightly bonded inside the solid (c) Lies in the innermost orbits and cannot be made free(d) Lies in the outermost orbits and cannot be made free

A

Q. No

Question Answer

30 At absolute zero (0 K) conduction band will be

(e) Fully occupied by electrons(f) Completely empty(g) Partially occupied by electrons(h) Partially occupied by holes

B

31 Above absolute zero, what is true for metals?

(a) Conduction band is always empty

C

(b) Valence band is always empty(c) Conduction band is partially occupied(d) Valence band is always full

32 For metals conduction band and valence band are

(e) Fully occupied(f) Empty(g) Partially occupied(h) Overlapping

D

33 For a metal which is the incorrect statement?

(a) Electrons are freely moving in the solid and have energy greater than valence electrons

(b) Electrons can remain simultaneously in conduction band and valence band

(c) Electrons in valence band may have energy equal to conduction band

(d) Electrons in valence band cannot have energy equal to conduction band

D

34 What is the correct statement for an insulator?

(a) The band gap energy is very high(b) The conduction band and valence cannot overlap(c) The conduction band and valence band may overlap(d) The conduction band and valence cannot have very little

difference of energy

B

35 Pure silicon at 0 K is an

(a) Intrinsic semiconductor (b) Extrinsic semiconductor. (c) Metal(d) Insulator

D

36 The energy required to break a covalent bond in a semiconductor

(a) is equal to 1 eV (b) is equal to the width of the forbidden gap(c) is greater in Ge than in Si(d) is the same in Ge and Si

B

37 As electrons in conduction band have high energy, where is their location in solids?

(a) Always near the top of the crystal (b) Always at the surface of the crystal(c) Anywhere in the solid moving freely

C

(d) Always bound to its parent atom in outermost orbit

Q. No

Question Answer

38 At 0 K, all the valence electrons in an intrinsic semiconductor

(a) are in the valence band (b) are in the forbidden gap (c) are in the conduction band (d) are free electrons

A

39 P-type and N-type extrinsic semiconductors are formed by adding impurities of valency?

(a) 5 and 3 respectively. (b) 5 and 4 respectively. (c) 3 and 5 respectively. (d) 3 and 4 respectively.

C

40 In an insulator, the forbidden energy gap is of the order of

(a) 1 MeV(b) 0.1 MeV(c) eV(d) 5 eV

D

41 At 0 K temperature, a p-type semiconductor

(a) Does not have any charge carriers(b) Has few electrons and few free holes(c) Has few holes but no electrons(d) Has equal number of holes and electrons

A

42 The bond that exists in a semiconductor is

(a) Ionic bond(b) Covalent bond(c) Metallic bond(d) Hydrogen bond

B

43 A pure semiconductor behaves slightly as a conductor at

(a) Only at very high temperatures (b) Only above room temperature

C

(c) At any energy above 0 K(d) Only at room temperature

44 Fermi level for a metal is

(q) Highest energy level occupied by electrons at 0 0C(r) Average value of all available energy levels(s) Highest energy level occupied by electrons at 0 K(t) Addition of energy of all available electron energy levels

A

45 Fermi level for an intrinsic semiconductor is

(a) Highest energy level occupied by electrons at 0 0C(b) Average value of all available energy levels(c) Highest energy level occupied by electrons at 0 K(d) Reference energy level at the centre of the forbidden energy gap

D

Q. No

Question Answer

46 What is the position of Fermi level in an n-type semiconductor?

(a) In between energy levels of conduction band and donor atoms(b) In between energy levels of donor atoms and Fermi energy

levels (c) In between energy levels of valence band and Fermi level(d) Close to the valence band

B

47 The Fermi Function represents the probability of occupation which of the following energy level by an electron?

i) For electrons only at Fermi energy level j) For electrons at any energy level k) For electrons only above Fermi energy level l) For electrons only below Fermi energy level

B

48 Fermi level represents the energy level with probability of its occupation of

(a) 0 % (b) 25 % (c) 50 % (d) 100 %

C

49 The probability of occupancy of electrons above Fermi level at T=0°K is

(a) 0 %(b) 25% (c) 50%(d) 100%

A

50 The probability of occupancy of electrons below Fermi level at T=0°K is

(a) 0 %(b) 25% (c) 50%(d) 100%

D

51 The energy level of a donor atom typically lies very close to

(a) Just above the conduction band(b) just below the conduction band(c) just above the valence band(d) just below the valence band

B

52 The energy level of a acceptor atom typically lies very close to

(a) just above the conduction band(b) just below the conduction band(c) just above the valence band(d) just below the valence band

C

53 Due to the addition of a donor atom the original Fermi energy level in an intrinsic semiconductor

(a) moves toward conduction band(b) moves toward valence band(c) remains at the centre of the forbidden energy gap(d) is not affected

A

Q. No

Question Answer

54 Due to the addition of an acceptor atom the original Fermi energy level in an intrinsic semiconductor

(a) moves toward conduction band

B

(b) moves toward valence band(c) remains at the centre of the forbidden energy gap(d) is not affected

55 The free electron theory could not explain which of the following properties?

(a) Electrical and thermal conductivity of metals

(b) Thermal and thermal conductivity of non-metal(c) Ferromagnetism(d) Ohm’s law

C

56 Free electron theory is based on which of the following assumption?

(e) Electrons are freely moving only at the centre of the solid(f) Electrons behaves are freely moving through entire the solid(g) Electrons can move freely only at the top surface of the solid(h) Electrons can move freely only along the surfaces of the solid

B

57 Which statement is correct regarding the influence of temperature on conductivity?

(e) Conductivity of metals increases with increase in temperature(f) Conductivity of metals decreases with increase in temperature(g) Conductivity of semiconductors decreases with increase in

temperature(h) Conductivity of semiconductors do not change with increase in

temperature

B

58 When light incidents on metals what is the effect on its conductivity?

(e) Conductivity almost remain constant with only little heating(f) Conductivity increases along with little heating of the material(g) Conductivity decreases along with little heating of the material(h) Conductivity decreases as electrons are emitted from the material

A

59 When light incidents on semiconductors what is the effect on its conductivity?

(e) Conductivity almost remain constant with little heating(f) Conductivity is not affected(g) Conductivity increases as electrons are promoted to conduction

band after absorbing light(h) Conductivity decreases as electrons absorb photons and move with

more random motion

D

60 What is the effect of impurity on metals?

(e) Impurity increases into increase of mobility of electrons

B

(f) Impurity result into more scattering of electrons and conductivity decreases

(g) Impurity result into more scattering of electrons and conductivity increases

(h) Impurity does not affect the conductivity

Q. No

Question Answer

61 Density of states function implies

(e) Number of available energy levels of electrons in unit volume per unit temperature

(f) Number of available energy levels of electrons in unit volume(g) Number of available energy levels of electrons in unit volume per

unit energy interval(h) Number of available electrons of per unit volume of the solid

C

62 Under the influence of external electric or magnetic field, when an electrons moves inside a solid what happens to its mass?

(e) The mass of electron is a constant quantity and it remains constant(f) The mass of electron increases due to absorption of external energy(g) The mass of electron increases or decreases depending on the

potential of positive ions(h) The external field will only change the resistance, but mass of

electron is not affected

C

63 What is the effect of at very high temperature on N-type semiconductors?

(e) Concentration of electrons and holes is almost equal due to ionization of donor ions and it turns into intrinsic semiconductor

(f) Concentration of electrons is more and it becomes more negative (g) More holes are created as electrons become free and it turns into

P-type semiconductor(h) It turns more negative as more electrons will break the bonds and

become free

A

64 What is the effect of at very high temperature on P-type semiconductors?

(e) Concentration of electrons and holes is almost equal due to ionization of donor ions and it turns into intrinsic semiconductor

(f) Concentration of holes is more and it becomes more positive(g) More electrons are created and it turns into N-type

A

semiconductor(h) It turns more positive as more electrons will break the bonds and

more holes are created

65 What is the effect of very high temperature on N-type semiconductors?

(e) Fermi level continue to increases as more electrons are free and conducting

(f) Fermi level continue to decreases as more electrons are free creating more holes

(g) Fermi level becomes equal to its intrinsic Fermi level is concentration of holes and electrons is balanced

(h) Fermi level is unbalanced and fluctuates rapidly

C

Q. No

Question Answer

67 If the doping concentration of donor ions increased, what is the effect on Fermi energy of N-type semiconductor?

(e) Fermi level increase but always remain below the energy level of conduction band

(f) Fermi level increases and merge into energy level of conduction band

(g) Fermi level increase and goes above the energy level of conduction band


B

68 If the doping concentration of acceptor ions increased, what is the effect on Fermi energy of P-type semiconductor?

(e) Fermi level decreases but always remain above the energy level of valence band

(f) Fermi level decreases and merge into energy level of valence band

(g) Fermi level decreases increase and goes down the energy level of valence band


B

69 What is true regarding drift current?

(e) Drift current is caused because of unequal concentration of electrons within the solid

(f) Drift current is caused because of unequal concentration of holes within the solid

(g) Drift current is caused due to smooth flow of electrons within the solid

(h) Drift current is caused because of random motion of electrons with ions or electrons

D

70 What is true regarding diffusion?

(e) Diffusion is caused because of random movement of electrons and holes within the solid

(f) Diffusion is caused due removal of electrons in solid when power supply is connected

(g) Diffusion is passing of electrons and holes through potential barrier

(h) Diffusion is caused because of unbalanced distribution of concentration of electrons or holes within the solid

D

71 If the density of charge carriers is increased, the value of Hall coefficient


A

72 If the current flowing through the semiconductor slab along its length, Hall voltage and electric field developed is due to accumulation of charge carriers

(e) Along opposite edges of its thickness(f) Along opposite edges of its width(g) Along opposite edges of its length(h) Along the ends from where current enters

B

Q. No

Question Answer

73 For silicon doped with trivalent impurity, C

(a) ne >> nh (b) ne > nh (c) nh >> ne (d) nh > ne

74 The Fermi level in an n-type semiconductor at 00 K lies

(a) Below the donor level.(b) Half way between the bottom of conduction band and donor

level.(c) Exactly in the middle of hand gap.(d) Half way between the top of valence band and the acceptor level.

B

75 If the Fermi energy of silver at 00 K is 5 electron volt, the mean energy of electron in silver at 00 K is

(a) 6 electron volt. (b) 12 electron volt.(c) 1.5 electron volt. (d) 3 electron volt.

D

76 The probability of occupation of an energy level E, when E – EF = kT, is given by

(a) 0.73(b) 0.63 (c) 0.5 (d) 0.27

D

77 Which of the following elements is a covalently bonded crystal?

(a) aluminium(b) sodium chloride(c) germanium (d) lead

C

78 The Fermi level is

(a) an average value of all available energy levels.

D

(b) an energy level at the top of the valence band.(c) the highest occupied energy level at 0 0c.(d) the highest occupied energy level at 0 0k.

79 Mobility of electron is

(a) Average flow of electrons per unit field.(b) Average applied field per unit drift velocity.(c) Average drift velocity per unit field.(d) Reciprocal of conductivity per unit charge.

C

Q. No

Question Answer

80 Fermi level represents the energy level with probability of its occupation of

(a) 0 %. (b) 25 %.(c) 50 %.(d) 100 %.

C

81 Hall effect can be used to measure

(a) mobility of semiconductors. (b) conductivity of semiconductors.(c) resistivity of semiconductors.(d) (d) all of these

D

82 The energy required to break a covalent bond in a semiconductor

(a) is equal to 1 eV (b) is equal to the width of the forbidden gap(c) is greater in Ge than in Si (d) is the same in Ge and Si

B

83 At absolute zero temperature, the probability of finding an electron at an energy level E is zero when

B

(a) E < EF(b) E > Ef(c) 2E E = f (d) None

84 Electrical conductivity of insulators is in the range of _______.

(a) 10-10(Ω-mm)-1(b) 10-10(Ω-cm)-1(c) 10-10(Ω-m)-1(d) 10-8(Ω-m)-1

A

85 Units for electric field strength

(a) A/cm2 (b) mho/meter(c) cm2/V.s(d) V/cm

C

86 Energy band gap size for semiconductors is in the range ________ eV.

(a) 1-2(b) 2-3 (c) 3-4 (d) > 4

B

Q. No

Question Answer

87 Energy band gap size for insulators is in the range ________ eV.

(a) 1-2(b) 2-3 (c) 3-4(d) (d) > 4

D

88 Flow of electrons is affected by the following

(a) Thermal vibrations(b) Impurity atoms (c) Crystal defects (d) (d) all

D

89 Flow of electrons is affected by the following

(a) Thermal vibrations(b) Impurity atoms (c) Crystal defects (d) (d) all

D

90 Fermi energy level for p-type extrinsic semiconductors lies

(a) At middle of the band gap(b) Close to conduction band(c) Close to valence band (d) (d) None

B

91 Fermi energy level for n-type extrinsic semiconductors lies


B

92 Fermi energy level for intrinsic semiconductors lies


C

93 Not an example for intrinsic semiconductor

(a) Si(b) Al (c) Ge(d) (d) Sn

A

94 In intrinsic semiconductors, number of electrons __________ number of holes.

(a) Equal(b) Greater than(c) Less than

C

(d) (d) Can not define

Q. No

Question Answer

95 In p-type semiconductors, number of holes __________ number of electrons.

(a) Equal(b) Greater than(c) Less than (d) (d) Twice

A

96 Mobility of holes is ___________ mobility of electrons in intrinsic semiconductors.

(a) Equal(b) Greater than (c) Less than(d) (d) Can not define

D

97 Fermi level for extrinsic semiconductor depends on

(a) Donor element(b) Impurity concentration (c) Temperature(d) (d) All

D

98 To measure light intensity we use

(a) LED with forward bias(b) LED with reverse bias(c) photodiode with reverse bias (d) (d) photodiode with forward bias

C

99 In integrated circuits, npn construction is preferred to pnp construction because

(a) npn construction is cheaper (b) to reduce diffusion constant, n-type collector is preferred(c) npn construction permits higher packing of elements(d) (d) p-type base is preferred

B

10 The photoelectric work function of a surface is 2.2 eV. The D

0 maximum kinetic energy of photo electrons emitted when light of wave length 6200 A.U. is incident on the surface is

(a) 1.6 eV (b) 1.4 eV (c) 1.2 eV (d) (d) Photo electrons are not emitted

101

A metallic surface is irradiated by monochromatic light of frequency ν1and stopping potential is found to be V1. If light of frequency ν2 irradiates the surface, the stopping potential will be

(a) (a) V1 + (h/e) (ν1 + ν2)(b) V1 + (h/e) (ν2 – ν1)(c) V1 + (e/h) (ν2 – ν1) (d) (d) V1 - (h/e) (ν1 + ν2)

B

Q. No

Question Answer

102

The retarding potential required to stop the emission of photoelectrons when a photosensitive material of work function 1.2 eV is irradiated with ultraviolet rays of wave length 2000 A.U. is

(a) 4V(b) 5V (c) 6V (d) (d) 8V

B

103

The photoelectric effect is __________.

(a) a relativistic effect(b) the production of current by silicon solar cells when exposed to

sunlight(c) the total reflection of light by metals giving them their typical

luster (d) (d) the ejection of electrons by a metal when struck by lightens

D

104

Substances which allow electric current to pass through them are called

A

(a) Conductors(b) insulation (c) semi conductors(d) (d) none of the above

105

A copper wire of length l and diameter d has potential difference V applied at its two ends. The drift velocity is vd. If the diameter of wire is made d/3, then drift velocity becomes

(a) 9 vd (b) vd / 9 (c) vd /3 (d) (d) vd.

D

106

The unit of electrical conductivity is

(a) mho / metre (b) mho / sq. m (c) ohm / metre (d) (d) ohm / sq. m.

A

107

All good conductors have high

(a) resistance (b) electrical conductivity (c) electrical and thermal conductivity (d) (d) conductance.

D

108

A silicon sample is uniformly doped with 1016 phosphorus atoms/cm3 and 2 × 1016 boron atoms/cm3. If all the dopants are fully ionized, the material is:

(a) n-type with carrier concentration of 3 × 1016/cm3

(b) p-type with carrier concentration of 1016/cm3A (c) p-type with carrier concentration of 4 × 1016/cm3(d) Intrinsic

B

Q. No

Question Answer

109

Measurement of Hall coefficient enables the determination of:

(a) Mobility of charge carriers(b) Type of conductivity and concentration of charge carriers(c) Temperature coefficient and thermal conductivity

B

(d) (d) None of the above110

The probability that an electron in a metal occupies the Fermi-level, at any temperature (>0 K) is:

(a) 0(b) 1(c) 0.5(d) (d) None of these

C

111

the conductivity of an intrinsic semiconductor is given by (symbols have the usual meanings):

(a) σi = eni2 (µn – µp)

(b) σi = eni (µn – µp)(c) σi = eni (µn + µp)(d) (d) none of the above

C

112

The Hall coefficient of sample (A) of a semiconductor is measured at room temperature. The Hall coefficient of (A) at room temperature is 4×10–4 m3 coulomb–1. The carrier concentration in sample A at room temperature is:

(a) ~ 1021 m–3

(b) ~ 1020 m–3

(c) ~ 1022 m–3

(d) (d) None of the above

C

113

If the drift velocity of holes under a field gradient of 100v/m is 5m/s, the mobility (in the same SI units) is

(a) 0.05(b) 0.55(c) 500(d) (d) 50

A

114

The Hall Effect voltage in intrinsic silicon is:

(a) Positive(b) Zero(c) Negative(d) None of the above

C

11 The Hall coefficient of an intrinsic semiconductor is: B

5

(a) Positive under all conditions(b) Negative under all conditions(c) Zero under all conditions(d) (d) None of the above

116

Consider the following statements: pure germanium and pure silicon are examples of: 1. Direct band-gap semiconductors 2. Indirect band-gap semiconductors 3. Degenerate semiconductors which of these statements are true

(a) 1 alone is correct(b) 2 alone is correct(c) 3 alone is correct(d) (d) None of the above

A

117

When ne and nh are electron and hole densities, and µe and µn are the carrier mobilities, the Hall coefficient is positive when

(a) nh µh > neµe

(b) nh µh2 > neµe

2

(c) nhµh < neµh


B

118

The electron and hole concentrations in a intrinsic semiconductor are ni and pi respectively. When doped with a p-type material, these change to n and p, respectively. Then:

(a) n + p = ni + pi

(b) n + ni = p + pi

(c) np = nipi


C

119

If the temperature of an extrinsic semiconductor is increased so that the intrinsic carrier concentration is doubled, then:

(a) The majority carrier density doubles(b) The minority carrier density doubles(c) Both majority and minority carrier densities double(d) (d) None of the above

C

120

The mobility is given by (notations have their usual meaning): A

(a) µ = V0/E0

(b) µ = V02/E0

(c) µ = V0/E02

(d) None of the above

Q. No

Question Answer

121

A sample of n-type semiconductor has electron density of 6.25 x 1018/cm3 at 300K. If the intrinsic concentration of carriers in this sample is 2.5 x 1013/cm3, at this temperature, the hole density becomes:

(a) 1016/cm3

(b) 107/cm3

(c) 1017/cm3


B

122

The intrinsic carrier density at 300K is 1.5 x 1010/cm3 in silicon. For n-type silicon doped to 2.25 x 1015 atoms/cm3, the equilibrium electron and hole densities are:

(a) n0 = 1.5 x 1016/cm3, p0 = 1.5 x 1012/cm3

(b) n0 = 1.5 x 1010/cm3, p0 = 2.25 x 1015/cm3

(c) n0 = 2.25 x 1017/cm3, p0 = 1.0 x 1014/cm3


D

123

In a p-type silicon sample, the hole concentration is 2.25 x 1015/cm3. If the intrinsic carrier concentration 1.5 x 1010/cm3, the electron concentration is

(a) 1021/cm3

(b) 1010/cm3

(c) 1016/cm3


D

div-a.weebly.comdiv-a.weebly.com/uploads/2/2/6/9/22691584/unit_iv.docx · Web viewA diode is a...

Documents

Transcript of div-a.weebly.comdiv-a.weebly.com/uploads/2/2/6/9/22691584/unit_iv.docx · Web viewA diode is a...