File - DIV-A

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SEMICONDUCTOR PHYSICS
Q.1) Electrical conductivity in between conductors & insulators is 1
a) high conductors
b) low conductors
c) 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
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
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 base
Q.8) Diamond acts as an 1
a) Conductor
c) Semiconductor
1
1
b) Insulator
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
a) 10-12 to 109Ωcm
b) 10-14 to 108Ωcm
c) 10-10 to 108Ωcm
d) 10-15 to 10-20Ωcm
1
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) 2.5eV
c) 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 crystal
Q.28) Semiconductor devices are 1
a) temperature dependant.
c) current dependant.
b) voltage 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 index
c) 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) Al
c)B
d) Mg
Q.33) At OoK, intrinsic semiconductor behaves as 1
a) a perfect conductor
c) a semiconductor
b) a super conductor
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
c) mobile ions
b) protons
d) immobile ions
Q.41) The major constituent of transistor are 1
a) salts
c) conductors
b) transistor
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
c) electrical energy
b) mechanical 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
.
3
MCQ Questions
4
In a semiconductor, current conduction is due 1
A) to only holes
B) to only free electrons
C) to both holes and free electrons
D) none of the above
C
5
The battery connection required to forward bias a p-n junction are 1
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
D) none of the above
A
6
The barrier voltage of a pn junction for germanium is about 1
A) 1.1V
B) 3V
C) 0
D) 0.3V
When the crystal diode current is large, the bias is 1
A) forward
B)inverse
C)poor
D)reverse
D
A zener diode is always _________connected. 1
A) forward
B)reverse
C)either forward/ reverse
D) none of the above
B
9
11
Remark
s
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
A
15
A semiconductor has ___________temperature coefficient of
resistance. 1
A) positive
B)0
C)negative
D) none of the above
C
16
When a pure semiconductor is heated, It’s resistance 1
A) goes up
B) goes down
C) remains the same
D) can not say
B
18
At T=0°K, all energy states below EF (i.e. E<EF) have a probability of
occupancy is 1
A) zero
B)unity
C)1/2
D) none of the above
B
19
At T=0°K, all energy states above EF (i.e. E>EF) have a probability of
occupancy is 1
A) zero
B)unity
C)1/2
D) none of the above
A
20
At T>0°K and E= EF , probability of occupancy is 1
A) zero
B)unity
C)1/2
D) none of the above
C
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) 6.2*1021 atoms
B) 6.2*1020 atoms
C) 7*1020 atoms
D) 7*1021atoms
A
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) 4.1*10-4 mho/m
A
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
A) nearer to valence band
B) nearer to conduction band
C)at the middle of the band gap
D) none of the above
C
24
In N type semiconductor Fermi level 1
A) is at the middle of band gap
B) gets shifted towards the conduction band
C) gets shifted towards the valence band
D) none of the above
B
25
In P type semiconductor Fermi level 1
A) is at the middle of band gap
B) gets shifted towards the conduction band
C) gets shifted towards the valence band
D) none of the above
C
26
N type semiconductor is
A) –Vely charged
B) +Vely charged
C) electrically neutral
D) none of the above
C
27
Silicon is 1
A) Trivalent
B) Pentavalent
C)Tetravalent
D) none of the above
C
28
In case of solar cell, the conversion efficiency 1
A) decreases with increasing temperature
B) increases with increasing temperature
C) decreases with decreasing temperature
D) increases with decreasing temperature
A
29
In case of solar cell,open circuit voltage 1
A)decreases with increasing temperature
B) increases with increasing temperature
C) decreases with decreasing temperature
A
1
D) increases with decreasing temperature
30
The Fill Factor of the solar cell is defined as 1
A) Fill Factor =(Isc*Voc) /( Im* Vm)
B) Fill Factor =(Isc*Voc)
C) Fill Factor =( Im* Vm)
D) Fill Factor =( Im* Vm)/(Isc*Voc)
D
38
A diode is a non-linear device due to the fact that 1
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
B
39
A hole in a semiconductor is defined as
A) a free electron
B) a free proton
C) the incomplete part of an electron pair bond
D) a free neutron
C
40
As the doping to a pure semiconductor increases, the bulk resistance of
the semiconductor 1
A) remains the same
B) increases
C) decreases
D)None of these
C
41
A hole and electron in close proximity woul tend to 1
A) repel each other
B) attract each other
C) have no effect on each other
D) None of these
B
43
In the depletion region of pn junction, there is a shortage of 1
A) acceptor ions
B) holes and electrons
C) donor ions
D) None of the above
B
44
A reverse biased pn junction has 1
A) very narrow depletion layer
B) almost no current
C) very low resistance
D) large current flow
B
45
A pn junction acts as a 1
A) controlled switch
B) bidirectional switch
C) unidirectional switch
D) None of the above
C
47
At room temperature, an intrinsic semiconductor has 1
A) many holes only
B) a few electrons and holes
C) many free electrons only
D) no holes or free electrons
B
48
At absolute temperature, an intrinsic semiconductor has 1
A) many holes only
B) a few electrons an holes
C) many free electrons only
D) no holes or free electrons
D
49
At room temperature, an intrinsic silicon crystal acts approximately as
1
A) a battery
B) a conductor
C) an insulator
D) a piece of copper wire
C
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
A) The resistance of intrinsic semiconductors decreases with increase of
temperature
C
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
A)Doping
B)Diffusion
C)barrier potential
D)Ions
B
57
What is an energy gap? 1
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
A
59
In "n" type material, majority carriers would be: 1
A) A)Holes
D
B) B)Dopants
C) Slower
D) Electrons
60
Elements with 1, 2, or 3 valence electrons usually make excellent: 1
A)Conductors
B)Semiconductors
C)Insulators
D)Neutral
A
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)Carbon
B)Ceramic
C)Mica
A
D)Argons
67
Electrons in the outermost orbit or shell of an atom are called 1
A)free electrons
B)negative ions
C)valence electrons
D)conduction band electrons
C
68
A pn junction allows current flow when 1
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
A
70
Intrinsic semiconductor material is characterized by a valence shell of
how many electrons? 1
A)1
B)2
C)4
D)6
C
71
Ionization within a P-N junction causes a layer on each side of the
barrier called the: 1
A)Junction
B)depletion region
C)barrier voltage
D)forward voltage
B
72
When a diode is forward biased, the voltage across it 1
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
D
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
A)majority carriers
B)Ions
C)Holes
A
C
D)free electrons
79
What electrical characteristic of intrinsic semiconductor material is
controlled by the addition of impurities? 1
A)Conductivity
B)Resistance
C)Power
D)all of the above
A
80
In "p" type material, minority carriers would be: 1
A)Holes
B)Dopants
C)Slower
D)Electrons
D
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
Minority carriers are many times activated by: 1
A
A) 1
B) 2
C) 3
D) 4
87
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) Potential is zero
A
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
A) Electrons
B) Protons
C) Mobile ions
D
D) immobile ions
96
Hall effect cannot explain 1
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
D
97
When a p-n junction diode is forward biased, then 1
A) the depletion region is reduced and barrier height is increased
C
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
A) Type of bonding
D
B) Crystal structure
C) Scattering mechanism with temperature
D) No. of charge carriers with temperature
10
2
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
10
4
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
11
1
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
11
2
___ occurs when a pn junction is first formed. 1
A) Recombination
B) Covalent bonding
C) Crystallization
D) Breakdown
11
4
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
A) n-type with carrier concentration of 3 × 1016/cm3
B
B) p-type with carrier concentration of 1016/cm3
C) p-type with carrier concentration of 4 × 1016/cm3
D) Intrinsic
11
5
n-type semiconductors are: 1
A) Negatively charged
B) Produced when Indium is added as an impurity to Germanium
C
C) Produced when phosphorous is added as an impurity to silicon
D) None of the above
11
6
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
D) None of the above
11
7
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
D) None of the above
11
9
The conductivity of an intrinsic semiconductor is given by (symbols
have the usual meanings): 1
A) σi = eni2 (µn – µp)
C
B) σi = eni (µn – µp)
C) σi = eni (µn + µp)
D) None of the above.
12
1
In an intrinsic semiconductor, the mobility of electrons in the
conduction band is: 1
A) Less than the mobility of holes in the valence band
B) Zero
C) Greater than the mobility of holes in the valence band
D) None of the above
C
12
2
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
A) ~ 1021 m–3
C
B) ~ 1020 m–3
C) ~ 1022 m–3
D) None of the above
12
3
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
D) None of the above
124
The Hall Effect voltage in intrinsic silicon is: 1
A) Positive
C
B) Zero
C) Negative
D) None of the above
12
5
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
D) None of the above
12
9
If the temperature of an extrinsic semiconductor is increased so that
the intrinsic carrier concentration is doubled, then: 1
A) The majority carrier density doubles
C
B) The minority carrier density doubles
C) Both majority and minority carrier densities double
D) None of the above
13
0
At room temperature, the current in an intrinsic semiconductor is due
to 1
A) Holes
C
B) Electrons
C) Holes and electrons
D) None of the above
13
1
The mobility is given by (notations have their usual meaning): 1
A
A) µ = V0/E0
B) µ = V02/E0
C) µ = V0/E02
D) None of the above
13
2
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 direction normal to both current and magnetic field
A
B) The direction of current
C) A direction anti parallel to magnetic field
D) None of the above
13
4
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
A) 1016/cm3
B) 107/cm3
B
C) 1017/cm3
D) None of the above
13
5
The intrinsic carrier density at 300K is 1.5 x 1010/cm3 in silicon. For ntype silicon doped to 2.25 x 1015 atoms/cm3, the equilibrium electron
and hole densities are: 2
A) n0 = 1.5 x 1016/cm3, p0 = 1.5 x 1012/cm3
D
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) None of the above
13
8
Measurement of Hall coefficient in a semiconductor provides
information on the: 1
A) Sign and mass of charge carriers
D
B) Mass and concentration of charge carriers
C) Sign of charge carriers alone
D) Sign and concentration of charge carriers
14
1
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
14
4
Current in a Metal is due to______________ 1
C
A) Protons
B) neutrons
C) electrons
D) holes
14
Flow of Current in a semi conductor is due to__________
D
5
A) Protons
B) electrons
C) Holes
D) both C & B
14
6
Currrent Produced in a metal when constant Electric field is applied is
_________ 1
A) pure Currrent
D
B) impure Current c
C) Diffusion Current
D) Drift Current
14
8
At Higher Energies Number Of Forbidden Energy Levels in a
Metal_______ 1
B
A) 1
B) 0
C) 2
D) infinite
14
9
Energy gap of semi conductors is Expressed in(units)__________ 1
D
A) joules
B) coulombs
C) ergs
D) electron volts
15
0
Energy Gap of conductors is _____________1
A) 0 eV
B) 1 eV
A
C) infinite
D) -1 eV
15
1
Conductivity of Intrinsic semi conductors depend up on _________1
A
A) Temperature
B) band Gap
C) both A and B
D) None of these
15
2
Resistance of Semiconductor___________1
B
A) Increases with temperature
B) decreases with temperature
C) independent of temperature
D) none
15
3
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
15
4
The probability of an electron occupying an energy level below Fermi
level is 1
A) 0%
B) 100%
C) 50%
D) 30%
B
15
5
The probability of an electron occupying an energy level above Fermi
level is 1
A
A) 0%
B) 100%
C) 50%
D) 30%
15
6
Fermi-Dirac statistics deal with particles of spin
1
B
A) 0
B) 1/2
C) 1
D) 2
15
8
In a metal, if the temperature is increased then resistivity 1
A
A) increases
B) decreases
C) remains same
D) none of these
16
1
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
A) 1,000
B) 2,000
C) 50
D) None of the above
D
16
4
The Fermi factor for E = EF at any temperature is 1
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
B
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 …….1
a) 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
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
d) A extrinsic
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) density
17) 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
10. d
3. d
11 c
4. d
5. b
6. a
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
7. d
8. d
9.
c
(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
(c) 2 eV
(b) 0.7 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)
I9. (b)
20. (a)
25. (c)
26. (c) 27. (b)
31. (a)
32. (b)
37. (a)
38. (a)
16. (c)
17. (a)
18. (a)
22. (a) 23. (c)
24. (c)
29. (b)
30. (a)
33. (a)
34. (b) 35. (b)
36. (a)
39. (b)
40. (a)
21. (a)
28. (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)
Q.3
105. (d)
106. (a) and (b)
107. (c)
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
Question
N
o
Which
1
of the following statements correctly describes a metal within band theory?1
(a) A material possessing moderate band gap
A
n
s
w
e
r
c
(b) A material possesses a large band gap
(c) A material with zero band gap
(d) A material with infinite band gap
Which
2
is the correct ordering of the band gaps energy?1
(a)
(b)
(c)
(d)
Diamond > silicon > copper
Diamond < silicon < copper
Diamond < silicon > copper
Diamond < silicon < copper
At60 Kelvin, semiconductors are1
(a)
(b)
(c)
(d)
a
Perfect metals
Perfect semiconductors
Perfect non-metals
Perfect insulator
d
Solids
8 with high value of conductivity are called:1
(a)
(b)
(c)
(d)
a
Conductors
Non-metal
Insulator
Semi conductor
At1absolute zero (0 K) conduction band will be1
0
(a)
(b)
(c)
(d)
B
Fully occupied by electrons
Completely empty
Partially occupied by electrons
Partially occupied by holes
For
1 metals conduction band and valence band are1
2
(a)
(b)
(c)
(d)
Q
No
2
D
Fully occupied
Empty
Partially occupied
Overlapping
Question
What happens to the Fermi energy level if a forward bias is applied to a
PN junction diode?1
Answer
B
(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
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
(c) Fermi energy levels remains in equilibrium in both regions to allow
current to flow
(d) Fermi energy levels increases for both the regions
A
4
When a P-type and N-type semiconductors are joined to form a PN
junction2
C
(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
5
In equilibrium state of a PN junction diode1
(a)
(b)
(c)
(d)
Fermi energy level of P-region is higher than that of N-region
Fermi energy level of N-region is lower than that of P-region
Fermi energy levels of both the regions are at minimum value
Fermi energy levels of both the regions attend thermal equilibrium
D
Q
No
4
Question
The Fermi Function represents the probability of occupation which of
the following energy level by an electron?1
a)
b)
c)
d)
Q
No
4
The Fermi Function represents the probability of occupation which of
the following energy level by an electron?
Q
No
1
Hall effect is true for 1
2
3
B
Answer
C
Metals only
Semiconductors only
Both metals and semiconductors
For N-type semiconductors only
Hall effect is true for1
(a)
(b)
(c)
(d)
Answer
For electrons only at Fermi energy level
For electrons at any energy level
For electrons only above Fermi energy level
For electrons only below Fermi energy level
Question
(a)
(b)
(c)
(d)
B
For electrons only at Fermi energy level
For electrons at any energy level
For electrons only above Fermi energy level
For electrons only below Fermi energy level
Question
e)
f)
g)
h)
Answer
A
Both N-type and P-type semiconductors
N-type Semiconductors only
P-type Semiconductors only
Metals only
When current flows along the length of the semiconductor slab and
magnetic field applied is perpendicular the length to Hall voltage
developed is
C
(a)
(b)
(c)
(d)
4
Along the length
Along the thickness
Along the width
Along the edges from where current enters
In Hall effect, if only the direction of the current is changed in the
material
B
(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
5
In Hall effect, if only the direction of the magnetic field applied to the
material is changed
C
(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
6
In Hall effect, if only the direction of the current is changed in the
material the Hall electric field
(a)
(b)
(c)
(d)
7
8
Hall electric field is developed in opposite direction
Hall electric field do not change the direction
Hall electric field increases
Hall electric field decreases
In Hall effect, if only the direction of the magnetic field is changed the
Hall electric field
(a)
(b)
(c)
(d)
A
D
There is no effect of Hall electric field
Hall electric field increases
Hall electric field decreases
Hall electric field is developed in opposite direction
If the thickness of the material is reduced, the Hall voltage developed
(a) Decreases
B
(b) Increases
(c) Remains constant
(d) Changes the direction
9
If the thickness of the material is increased, the Hall voltage developed
(a)
(b)
(c)
(d)
10
Decreases
Increases
Remains constant
Changes the direction
If the strength of magnetic field is increased, the Hall voltage developed
(a)
(b)
(c)
(d)
11
12
13
14
A
Decreases
Increases
Remains constant
Changes the direction
If the density of charge carriers is increased, the value of Hall voltage
(a)
(b)
(c)
(d)
B
Decreases
Increases
Remains constant
Changes the direction
If the magnitude of current is decreased, the Hall voltage developed
(e)
(f)
(g)
(h)
A
Decreases
Increases
Remains constant
Changes the direction
If the magnitude of current is increased, the Hall voltage developed
(a)
(b)
(c)
(d)
C
Decreases
Remains constant
Increases
Changes the direction
If the strength of magnetic field is decreased, the Hall voltage developed
(a)
(b)
(c)
(d)
A
Decreases
Increases
Remains constant
Changes the direction
A
15
If the density of charge carriers is increased, the value of Hall coefficient
(a)
(b)
(c)
(d)
16
Decreases
Increases
Remains constant
Changes the direction
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)
(b)
(c)
(d)
Q
N
o
The
1 free electron theory could not explain which of the following properties?
B
Electrons are freely moving only at the centre of the solid
Electrons behaves are freely moving through entire the solid
Electrons can move freely only at the top surface of the solid
Electrons can move freely only along the surfaces of the solid
Which
3
statement is correct regarding the influence of temperature on conductivity?
(a)
(b)
(c)
(d)
A
n
s
w
e
r
C
Electrical and thermal conductivity of metals
Thermal and thermal conductivity of non-metal
Ferromagnetism
Ohm’s law
Free
2 electron theory is based on which of the following assumption?
(a)
(b)
(c)
(d)
B
Along opposite edges of its thickness
Along opposite edges of its width
Along opposite edges of its length
Along the ends from where current enters
Question
(e)
(f)
(g)
(h)
A
B
Conductivity of metals increases with increase in temperature
Conductivity of metals decreases with increase in temperature
Conductivity of semiconductors decreases with increase in temperature
Conductivity of semiconductors do not change with increase in temperature
When
4 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
When
5 light incidents on semiconductors what is the effect on its conductivity?
(a)
(b)
(c)
(d)
Conductivity almost remain constant with little heating
Conductivity is not affected
Conductivity increases as electrons are promoted to conduction band after absorbing light
Conductivity decreases as electrons absorb photons and move with more random motion
What
6 is the effect of impurity on metals?
(a)
(b)
(c)
(d)
9
C
Number of available energy levels of electrons in unit volume per unit temperature
Number of available energy levels of electrons in unit volume
Number of available energy levels of electrons in unit volume per unit energy interval
Number of available electrons of per unit volume of the solid
Under
8 the influence of external electric or magnetic field, when an electrons moves inside a solid
what happens to its mass?
(a)
(b)
(c)
(d)
B
Impurity increases into increase of mobility of electrons
Impurity result into more scattering of electrons and conductivity decreases
Impurity result into more scattering of electrons and conductivity increases
Impurity does not affect the conductivity
Density
7
of states function implies
(a)
(b)
(c)
(d)
D
C
The mass of electron is a constant quantity and it remains constant
The mass of electron increases due to absorption of external energy
The mass of electron increases or decreases depending on the potential of positive ions
The external field will only change the resistance, but mass of electron is not affected
What is the effect of at very high temperature on N-type semiconductors?
A
(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
1
0
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
1
1
What is the effect of very high temperature on N-type semiconductors?
C
(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
1
2
What is the effect of very high temperature on P-type semiconductors?
C
(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
1
3
If the doping concentration of donor ions increased, what is the effect on Fermi energy of
N-type semiconductor?
(a)
(b)
(c)
(d)
1
4
Fermi level increase but always remain below the energy level of conduction band
Fermi level increases and merge into energy level of conduction band
Fermi level increase and goes above the energy level of conduction band
Fermi level is unbalanced and fluctuates rapidly
If the doping concentration of acceptor ions increased, what is the effect on Fermi energy
of P-type semiconductor?
(a)
(b)
(c)
(d)
1
5
1
6
D
Drift current is caused because of unequal concentration of electrons within the solid
Drift current is caused because of unequal concentration of holes within the solid
Drift current is caused due to smooth flow of electrons within the solid
Drift current is caused because of random motion of electrons with ions or electrons
What is true regarding diffusion?
(a)
(b)
(c)
(d)
B
Fermi level decreases but always remain above the energy level of valence band
Fermi level decreases and merge into energy level of valence band
Fermi level decreases increase and goes down the energy level of valence band
Fermi level is unbalanced and fluctuates rapidly
What is true regarding drift current?
(a)
(b)
(c)
(d)
B
Diffusion is caused because of random movement of electrons and holes within the solid
Diffusion is caused due removal of electrons in solid when power supply is connected
Diffusion is passing of electrons and holes through potential barrier
Diffusion is caused because of unbalanced distribution of concentration of electrons or
holes within the solid
D
Q
No
1
Question
The solar cell works
(e)
(f)
(g)
(h)
2
Answer
D
Only infra-red light rays
Only ultra-violet light rays
Only visible light rays
for entire range of electromagnetic spectrum
If anti-reflection coating is made over the solar cell
C
(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
3
In a solar cell short circuit current refers to
(a)
(b)
(c)
(d)
4
5
C
Maximum voltage when load resistance is minimum
Minimum voltage when load resistance is maximum
Maximum voltage when load resistance is maximum
Minimum voltage when load resistance is minimum
What is true regarding a solar cell
(a)
(b)
(c)
(d)
6
Maximum current when load resistance is minimum
Minimum current when load resistance is maximum
Maximum current when load resistance is maximum
Minimum current when load resistance is minimum
In a solar cell open circuit voltage refers to
(a)
(b)
(c)
(d)
A
D
It works only for sunlight and not for artificial light sources
It works only for monochromatic and coherent light
It works only for visible part of the spectrum
It works when any type of electromagnetic radiation falls over it
A solar cell converts ______
B
(a)
(b)
(c)
(d)
7
heat energy into electrical energy
solar energy into electrical energy
heat energy into light energy
solar energy into light energy
A solar cell works on the principle of
(a)
(b)
(c)
(d)
Photoelectric effect
Photovoltaic effect
Photoluminescence
Photo-combustion
B
8
The fill factor of a solar cell is the ratio of
(a)
(b)
(c)
(d)
9
Actual power output to theoretical power
Theoretical power to actual power output
Actual power output to incident power
Theoretical power to incident power
Efficiency of a solar cell is the ratio of
(a)
(b)
(c)
(d)
10
11
12
C
an current amplifier is used to connect solar cells
they are connected in parallel
they are connected in series
a voltage amplifier is used to connect solar cells
If the power incident on solar cell is increased
(a)
(b)
(c)
(d)
D
total output voltage of all solar cells
total fill factor of all solar cells
total efficiency of all solar cells
total output current of all solar cells
To have maximize the output from solar cells
(a)
(b)
(c)
(d)
C
Actual power output to theoretical power
Theoretical power to actual power output
Actual power output to incident power
Theoretical power to incident power
Solar cells are usually connected in an array. Which factor gets add up due to
this arrangement?
(a)
(b)
(c)
(d)
A
A
efficiency and fill factor both increases
efficiency and fill factor both decreases
efficiency increases but fill factor decreases
efficiency decreases but fill factor increases
Unit 4: Solid state Physics
MCQ Question Bank
Q.
No
Question
Answer
1
2
3
4
5
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 Ptype until equilibrium is obtained
(j) Fermi energy level increases for N-type while decreases for Ptype 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
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 Ptype
(f) Fermi energy level increases for N-type while decreases for Ptype
(g) Fermi energy levels remains in equilibrium in both regions to
allow current to flow
(h) Fermi energy levels increases for both the regions
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 Ptype
(f) Fermi energy level increases for N-type while decreases for Ptype
(g) Fermi energy levels remains in equilibrium in both regions to
allow current to flow
(h) Fermi energy levels increases for both the regions
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
In equilibrium state of a PN junction diode
A
B
A
C
D
(e)
(f)
(g)
(h)
6
Fermi energy level of P-region is higher than that of N-region
Fermi energy level of N-region is lower than that of P-region
Fermi energy levels of both the regions are at minimum value
Fermi energy levels of both the regions attend thermal
equilibrium
In an equilibrium state of an NPN transistor, what is true for
Fermi energy levels
C
7
(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)
For a biased NPN transistor, what is true for Fermi energy levels
A
8
(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)
Hall effect is true for
C
9
(m) Metals only
(n) Semiconductors only
(o) Both metals and semiconductors
(p) For N-type semiconductors only
Hall effect is true for
A
(e)
(f)
(g)
(h)
10
Both N-type and P-type semiconductors
N-type Semiconductors only
P-type Semiconductors only
Metals only
When current flows along the length of the semiconductor slab
and magnetic field applied is perpendicular the length to Hall
C
voltage developed is
(e)
(f)
(g)
(h)
11
Along the length
Along the thickness
Along the width
Along the edges from where current enters
In Hall effect, if only the direction of the current is changed in
the material
B
12
(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
In Hall effect, if only the direction of the magnetic field applied
to the material is changed
C
(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
13
In Hall effect, if only the direction of the current is changed in
the material the Hall electric field
(e)
(f)
(g)
(h)
Q.
No
14
15
Hall electric field is developed in opposite direction
Hall electric field do not change the direction
Hall electric field increases
Hall electric field decreases
Question
If the thickness of the material is reduced, the Hall voltage
developed
(e)
(f)
(g)
(h)
A
Decreases
Increases
Remains constant
Changes the direction
If the thickness of the material is increased, the Hall voltage
developed
(e) Decreases
Answer
B
A
16
(f) Increases
(g) Remains constant
(h) Changes the direction
If the strength of magnetic field is increased, the Hall voltage
developed
(e)
(f)
(g)
(h)
17
(e)
(f)
(g)
(h)
18
(i)
(j)
(k)
(l)
19
Decreases
Remains constant
Increases
Changes the direction
If the strength of magnetic field is decreased, the Hall voltage
developed
Decreases
Increases
Remains constant
Changes the direction
If the magnitude of current is increased, the Hall voltage
developed
Decreases
Increases
Remains constant
Changes the direction
If the magnitude of current is decreased, the Hall voltage
developed
C
A
B
A
(m) Decreases
(n) Increases
(o) Remains constant
(p) Changes the direction
20
21
If the density of charge carriers is increased, the value of Hall
voltage
(e) Decreases
(f) Increases
(g) Remains constant
(h) Changes the direction
Which of the following statements correctly describes a metal within
band theory?
(i) A material possessing moderate band gap
A
C
(j) A material possesses a large band gap
(k) A material with zero band gap
(l) A material with infinite band gap
Q.
No
22
Which is the correct ordering of the band gaps energy?
23
(e) Diamond > silicon > copper
(f) Diamond < silicon < copper
(g) Diamond < silicon > copper
(h) Diamond < silicon < copper
Which statement is true regarding electrical conductivity of materials?
24
(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
Which statement is incorrect at ordinary room temperature?
C
25
(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
Which statement is incorrect about semiconductors?
C
Question
A
B
(a)
(b)
(c)
(d)
26
A charge carrier may be either a positive hole or an electron
Ga-doped Si is a p-type semiconductor
n- and p-type semiconductors are intrinsic semiconductors
Doping Si with As introduces a donor level below the
conduction band
At 0 Kelvin, semiconductors are
Answer
(e) Perfect metals
(f) Perfect semiconductors
(g) Perfect non-metals
D
27
(h) Perfect insulator
In an intrinsic semiconductors, what is true of the following?
(a)
(b)
(c)
(d)
28
Concentration of electrons and hole is equal
Concentration of electrons is greater than holes
Concentration of holes is greater than electrons
Concentration of holes and electrons vary by very small amount
Solids with high value of conductivity are called:
(e)
(f)
(g)
(h)
29
(a)
(b)
(c)
(d)
A
Conductors
Non-metal
Insulator
Semi conductor
The electrons in valence band are
A
A
Freely moving inside the solid
Tightly bonded inside the solid
Lies in the innermost orbits and cannot be made free
Lies in the outermost orbits and cannot be made free
Q.
No
30
At absolute zero (0 K) conduction band will be
B
31
(e) Fully occupied by electrons
(f) Completely empty
(g) Partially occupied by electrons
(h) Partially occupied by holes
Above absolute zero, what is true for metals?
C
32
(a) Conduction band is always empty
(b) Valence band is always empty
(c) Conduction band is partially occupied
(d) Valence band is always full
For metals conduction band and valence band are
D
Question
(e)
(f)
(g)
(h)
33
Fully occupied
Empty
Partially occupied
Overlapping
For a metal which is the incorrect statement?
Answer
D
34
(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
What is the correct statement for an insulator?
(a)
(b)
(c)
(d)
35
(a)
(b)
(c)
(d)
36
(a)
(b)
(c)
(d)
37
(a)
(b)
(c)
(d)
Q.
No
38
B
The band gap energy is very high
The conduction band and valence cannot overlap
The conduction band and valence band may overlap
The conduction band and valence cannot have very little
difference of energy
Pure silicon at 0 K is an
D
Intrinsic semiconductor
Extrinsic semiconductor.
Metal
Insulator
The energy required to break a covalent bond in a semiconductor
B
is equal to 1 eV
is equal to the width of the forbidden gap
is greater in Ge than in Si
is the same in Ge and Si
As electrons in conduction band have high energy, where is their
location in solids?
C
Always near the top of the crystal
Always at the surface of the crystal
Anywhere in the solid moving freely
Always bound to its parent atom in outermost orbit
Question
At 0 K, all the valence electrons in an intrinsic semiconductor
(a) are in the valence band
Answer
A
39
(b) are in the forbidden gap
(c) are in the conduction band
(d) are free electrons
P-type and N-type extrinsic semiconductors are formed by
adding impurities of valency?
(a)
(b)
(c)
(d)
40
(a)
(b)
(c)
(d)
41
(a)
(b)
(c)
(d)
42
(a)
(b)
(c)
(d)
43
(a)
(b)
(c)
(d)
44
(q)
(r)
(s)
(t)
45
C
5 and 3 respectively.
5 and 4 respectively.
3 and 5 respectively.
3 and 4 respectively.
In an insulator, the forbidden energy gap is of the order of
D
1 MeV
0.1 MeV
eV
5 eV
At 0 K temperature, a p-type semiconductor
A
Does not have any charge carriers
Has few electrons and few free holes
Has few holes but no electrons
Has equal number of holes and electrons
The bond that exists in a semiconductor is
B
Ionic bond
Covalent bond
Metallic bond
Hydrogen bond
A pure semiconductor behaves slightly as a conductor at
C
Only at very high temperatures
Only above room temperature
At any energy above 0 K
Only at room temperature
Fermi level for a metal is
A
Highest energy level occupied by electrons at 0 0C
Average value of all available energy levels
Highest energy level occupied by electrons at 0 K
Addition of energy of all available electron energy levels
Fermi level for an intrinsic semiconductor is
D
(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
Q.
No
46
47
Question
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
The Fermi Function represents the probability of occupation
which of the following energy level by an electron?
i)
j)
k)
l)
48
(a)
(b)
(c)
(d)
49
(a)
(b)
(c)
(d)
50
For electrons only at Fermi energy level
For electrons at any energy level
For electrons only above Fermi energy level
For electrons only below Fermi energy level
Fermi level represents the energy level with probability of its
occupation of
0%
25 %
50 %
100 %
The probability of occupancy of electrons above Fermi level at
T=0°K is
0%
25%
50%
100%
The probability of occupancy of electrons below Fermi level at
T=0°K is
(a) 0 %
(b) 25%
(c) 50%
Answer
B
B
C
A
D
51
(d) 100%
The energy level of a donor atom typically lies very close to
(a)
(b)
(c)
(d)
52
(a)
(b)
(c)
(d)
53
(a)
(b)
(c)
(d)
Q.
No
54
55
56
Just above the conduction band
just below the conduction band
just above the valence band
just below the valence band
The energy level of a acceptor atom typically lies very close to
just above the conduction band
just below the conduction band
just above the valence band
just below the valence band
Due to the addition of a donor atom the original Fermi energy
level in an intrinsic semiconductor
B
C
A
moves toward conduction band
moves toward valence band
remains at the centre of the forbidden energy gap
is not affected
Question
Due to the addition of an acceptor 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
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
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
Answer
B
C
B
(h) Electrons can move freely only along the surfaces of the solid
57
Which statement is correct regarding the influence of temperature on
conductivity?
B
(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
58
When light incidents on metals what is the effect on its conductivity?
(e)
(f)
(g)
(h)
59
A
Conductivity almost remain constant with only little heating
Conductivity increases along with little heating of the material
Conductivity decreases along with little heating of the material
Conductivity decreases as electrons are emitted from the material
When light incidents on semiconductors what is the effect on its
conductivity?
D
(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
60
What is the effect of impurity on metals?
B
(e) Impurity increases into increase of mobility of electrons
(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
61
Question
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
Answer
C
(h) Number of available electrons of per unit volume of the solid
62
Under the influence of external electric or magnetic field, when
an electrons moves inside a solid what happens to its mass?
C
(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
63
What is the effect of at very high temperature on N-type
semiconductors?
A
(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
64
What is the effect of at very high temperature on P-type
semiconductors?
A
(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
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
67
Question
If the doping concentration of donor ions increased, what is the
effect on Fermi energy of N-type semiconductor?
Answer
B
(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
(h) Fermi level is unbalanced and fluctuates rapidly
68
If the doping concentration of acceptor ions increased, what is
the effect on Fermi energy of P-type semiconductor?
B
(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
(h) Fermi level is unbalanced and fluctuates rapidly
69
What is true regarding drift current?
D
(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
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
D
concentration of electrons or holes within the solid
71
If the density of charge carriers is increased, the value of Hall
coefficient
(e)
(f)
(g)
(h)
72
Q.
No
73
B
Along opposite edges of its thickness
Along opposite edges of its width
Along opposite edges of its length
Along the ends from where current enters
Question
For silicon doped with trivalent impurity,
(a)
(b)
(c)
(d)
74
Decreases
Increases
Remains constant
Changes the direction
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)
(f)
(g)
(h)
A
Answer
C
ne >> nh
ne > nh
nh >> ne
nh > ne
The Fermi level in an n-type semiconductor at 00 K lies
B
(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.
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
(d) 3 electron volt.
The probability of occupation of an energy level E, when E – EF
= kT, is given by
76
(a)
(b)
(c)
(d)
77
0.73
0.63
0.5
0.27
Which of the following elements is a covalently bonded crystal?
(a)
(b)
(c)
(d)
78
79
D
an average value of all available energy levels.
an energy level at the top of the valence band.
the highest occupied energy level at 0 0c.
the highest occupied energy level at 0 0k.
Mobility of electron is
(a)
(b)
(c)
(d)
Q.
No
80
C
Average flow of electrons per unit field.
Average applied field per unit drift velocity.
Average drift velocity per unit field.
Reciprocal of conductivity per unit charge.
Question
Fermi level represents the energy level with probability of its
occupation of
(a)
(b)
(c)
(d)
C
aluminium
sodium chloride
germanium
lead
The Fermi level is
(a)
(b)
(c)
(d)
D
0 %.
25 %.
50 %.
100 %.
Answer
C
81
(a)
(b)
(c)
(d)
82
(a)
(b)
(c)
(d)
83
D
mobility of semiconductors.
conductivity of semiconductors.
resistivity of semiconductors.
(d) all of these
The energy required to break a covalent bond in a semiconductor
B
is equal to 1 eV
is equal to the width of the forbidden gap
is greater in Ge than in Si
is the same in Ge and Si
At absolute zero temperature, the probability of finding an
electron at an energy level E is zero when
(a)
(b)
(c)
(d)
84
85
A
10-10(Ω-mm)-1
10-10(Ω-cm)-1
10-10(Ω-m)-1
10-8(Ω-m)-1
Units for electric field strength
(a)
(b)
(c)
(d)
B
E < EF
E > Ef
2E E = f
None
Electrical conductivity of insulators is in the range of _______.
(a)
(b)
(c)
(d)
86
Hall effect can be used to measure
C
A/cm2
mho/meter
cm2/V.s
V/cm
Energy band gap size for semiconductors is in the range
________ eV.
(a) 1-2
(b) 2-3
(c) 3-4
B
(d) > 4
Q.
No
87
(a)
(b)
(c)
(d)
88
(a)
(b)
(c)
(d)
89
(a)
(b)
(c)
(d)
90
(a)
(b)
(c)
(d)
91
(a)
(b)
(c)
(d)
92
(a)
(b)
(c)
(d)
Question
Answer
Energy band gap size for insulators is in the range ________ eV.
D
1-2
2-3
3-4
(d) > 4
Flow of electrons is affected by the following
D
Thermal vibrations
Impurity atoms
Crystal defects
(d) all
Flow of electrons is affected by the following
D
Thermal vibrations
Impurity atoms
Crystal defects
(d) all
Fermi energy level for p-type extrinsic semiconductors lies
B
At middle of the band gap
Close to conduction band
Close to valence band
(d) None
Fermi energy level for n-type extrinsic semiconductors lies
B
At middle of the band gap
Close to conduction band
Close to valence band
(d) None
Fermi energy level for intrinsic semiconductors lies
C
At middle of the band gap
Close to conduction band
Close to valence band
(d) None
93
Not an example for intrinsic semiconductor
(a)
(b)
(c)
(d)
94
(a)
(b)
(c)
(d)
Q.
No
95
(a)
(b)
(c)
(d)
96
(a)
(b)
(c)
(d)
97
(a)
(b)
(c)
(d)
98
Si
Al
Ge
(d) Sn
In intrinsic semiconductors, number of electrons __________
number of holes.
A
C
Equal
Greater than
Less than
(d) Can not define
Question
Answer
In p-type semiconductors, number of holes __________ number
of electrons.
A
Equal
Greater than
Less than
(d) Twice
Mobility of holes is ___________ mobility of electrons in
intrinsic semiconductors.
D
Equal
Greater than
Less than
(d) Can not define
Fermi level for extrinsic semiconductor depends on
D
Donor element
Impurity concentration
Temperature
(d) All
To measure light intensity we use
C
(a)
(b)
(c)
(d)
99
(a)
(b)
(c)
(d)
100
(a)
(b)
(c)
(d)
101
(a)
(b)
(c)
(d)
Q.
No
102
LED with forward bias
LED with reverse bias
photodiode with reverse bias
(d) photodiode with forward bias
In integrated circuits, npn construction is preferred to pnp
construction because
npn construction is cheaper
to reduce diffusion constant, n-type collector is preferred
npn construction permits higher packing of elements
(d) p-type base is preferred
The photoelectric work function of a surface is 2.2 eV. The
maximum kinetic energy of photo electrons emitted when light
of wave length 6200 A.U. is incident on the surface is
1.6 eV
1.4 eV
1.2 eV
(d) Photo electrons are not emitted
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
D
B
(a) V1 + (h/e) (ν1 + ν2)
V1 + (h/e) (ν2 – ν1)
V1 + (e/h) (ν2 – ν1)
(d) V1 - (h/e) (ν1 + ν2)
Question
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)
(b)
(c)
(d)
B
4V
5V
6V
(d) 8V
Answer
B
103
The photoelectric effect is __________.
D
(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
104
Substances which allow electric current to pass through them are
called
(a)
(b)
(c)
(d)
105
(a)
(b)
(c)
(d)
106
(a)
(b)
(c)
(d)
107
(a)
(b)
(c)
(d)
108
(a)
(b)
(c)
(d)
Conductors
insulation
semi conductors
(d) none of the above
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
D
9 vd
vd / 9
vd /3
(d) vd.
The unit of electrical conductivity is
A
mho / metre
mho / sq. m
ohm / metre
(d) ohm / sq. m.
All good conductors have high
D
resistance
electrical conductivity
electrical and thermal conductivity
(d) conductance.
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:
n-type with carrier concentration of 3 × 1016/cm3
p-type with carrier concentration of 1016/cm3A
p-type with carrier concentration of 4 × 1016/cm3
Intrinsic
B
Q.
No
109
Question
Measurement of Hall coefficient enables the determination of:
(a)
(b)
(c)
(d)
110
(a)
(b)
(c)
(d)
111
(a)
(b)
(c)
(d)
112
(a)
(b)
(c)
(d)
113
Mobility of charge carriers
Type of conductivity and concentration of charge carriers
Temperature coefficient and thermal conductivity
(d) None of the above
The probability that an electron in a metal occupies the Fermilevel, at any temperature (>0 K) is:
0
1
0.5
(d) None of these
the conductivity of an intrinsic semiconductor is given by
(symbols have the usual meanings):
σi = eni2 (µn – µp)
σi = eni (µn – µp)
σi = eni (µn + µp)
(d) none of the above
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:
~ 1021 m–3
~ 1020 m–3
~ 1022 m–3
(d) None of the above
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
Answer
B
C
C
C
A
114
(c) 500
(d) (d) 50
The Hall Effect voltage in intrinsic silicon is:
(a)
(b)
(c)
(d)
115
116
(a)
(b)
(c)
(d)
117
(a)
(b)
(c)
(d)
118
Positive
Zero
Negative
None of the above
The Hall coefficient of an intrinsic semiconductor is:
(a)
(b)
(c)
(d)
C
Positive under all conditions
Negative under all conditions
Zero under all conditions
(d) None of the above
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
1 alone is correct
2 alone is correct
3 alone is correct
(d) None of the above
When ne and nh are electron and hole densities, and µe and µn are
the carrier mobilities, the Hall coefficient is positive when
nh µh > neµe
nh µh2 > neµe2
nhµh < neµh
(d) None of the above
The electron and hole concentrations in a intrinsic
semiconductor are ni and pi respectively. When doped with a ptype material, these change to n and p, respectively. Then:
(a) n + p = ni + pi
(b) n + ni = p + pi
(c) np = nipi
B
A
B
C
119
(d) (d) None of the above
If the temperature of an extrinsic semiconductor is increased so
that the intrinsic carrier concentration is doubled, then:
(a)
(b)
(c)
(d)
120
(a)
(b)
(c)
(d)
Q.
No
121
(a)
(b)
(c)
(d)
122
(a)
(b)
(c)
(d)
123
The majority carrier density doubles
The minority carrier density doubles
Both majority and minority carrier densities double
(d) None of the above
The mobility is given by (notations have their usual meaning):
A
µ = V0/E0
µ = V02/E0
µ = V0/E02
None of the above
Question
Answer
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:
B
1016/cm3
107/cm3
1017/cm3
(d) None of the above
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:
D
n0 = 1.5 x 1016/cm3, p0 = 1.5 x 1012/cm3
n0 = 1.5 x 1010/cm3, p0 = 2.25 x 1015/cm3
n0 = 2.25 x 1017/cm3, p0 = 1.0 x 1014/cm3
(d) None of the above
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)
(b)
(c)
(d)
C
1021/cm3
1010/cm3
1016/cm3
(d) None of the above
D
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