Question Set B

CBSE 12th Physics Semiconductor Electronics: Materials, Devices and Simple Circuits Important Questions And Answers Study Material - QB365

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Questions:

Multiple Choice Question

62 x 1 = 62

During the formation of a p-n junction

(a)

diffusion current keeps increasing

(b)

drift current remains constant

(c)

both the diffusion current and drift current remain constant.

(d)

diffusion current remains almost constant but drift current increases till both currents-become equal

If a p-n junction diode is reverse biased.

(a)

the potential barrier is lowered

(b)

the potential barrier rermainsunaffected.

(c)

the potential barrier is raised

(d)

the current is mainly due to majority charge carriers.

The formation of depletion region in a p-n junction diode is due to

(a)

movement of dopant atoms

(b)

diffusion of the electrons and holes

(c)

drift of electrons only

(d)

drift of holes only

At a certain temperature in an intrinsic semiconductor, the electrons and holes concentration is 1.5 × 10¹⁶m^-3.When it is doped with a trivalent dopant, hole concentration increases to 4.5 \(\times\) 10²² m^-3. In the doped semiconductor, the concentration of electrons (n_e) will be

(a)

3 x 10⁶m^-3

(b)

5 x 10⁷m^-3

(c)

5 x 10⁹m^-3

(d)

6.75 x 10³⁸m^-3

The I-V characteristic of a p-n junction diode is shown below. The approximate dynamic resistance of the p-n junction when a forward bias of 2 volt is applied

(a)

1 Ω

(b)

0.25 Ω

(c)

0.5 Ω

(d)

5 Ω

If the following input signal is sent through a p-n junction diode, then the output signal across RL will be

(a)

(b)

(c)

(d)

Current in the circuit will be

(a)

5/40 A

(b)

5/50 A

(c)

5/10A

(d)

5/20 A

A 2V battery is connected across the points A and B as shown in the figure. Assuming that the resistance of each diode is zero in forward bias and infinity in reverse bias, the current supplied by the battery when its positive terminal is connected to A is

(a)

0.2 A

(b)

0.4 A

(c)

Zero

(d)

0.1 A

In a p-type semiconductor, there is

(a)

excess of one electron.

(b)

absence of one electron

(c)

a missing atom.

(d)

a donar level

10.

A p-type semiconductor can be obtained by adding

(a)

arsenic to pure silicon.

(b)

gallium to pure silicon

(c)

antimony to pure germanium.

(d)

phosphorus to pure germanium

11.

In the circuit shown in figure below, if the diode forward voltage drop is 0.3 V, the voltage difference between A and B is

(a)

1.3 V

(b)

2.3 V

(c)

(d)

0.5 V

12.

A full-wave rectifier circuit along with the input and output voltages is shown in the figure The contribution to output voltage from diode 2 is

(a)

A,C

(b)

B, D

(c)

B, C

(d)

A, D

13.

In the half-wave rectifier circuit shown. Which one of the following waveforms is true for VCD the output across C and D?

(a)

(b)

(c)

(d)

14.

The forbidden energy band gap in conductors, semiconductors and insulators are EG₁, EG₂ and EG₃respectively. The relation among them is

(a)

EG₁ = EG₂ = EG₃

(b)

EG₁ < EG₂ < EG₃

(c)

EG₁ > EG₂ > EG₃

(d)

EG₁ < EG₂> EG₃

15.

Electrical conductivity of a semiconductor

(a)

decreases with the rise in its temperature.

(b)

increases with the rise in its temperature

(c)

does not change with the rise in its temperature.

(d)

first increases and then decreases with the rise in its temperature

16.

The output of the given circuit in figure is given below.

(a)

would be zero at all times.

(b)

would be like a half-wave rectifier with positive cycles in output.

(c)

would be like a half-wave rectifier with negative cycles in output.

(d)

would be like that of a full-wave rectifier.

17.

In figure given, assuming the diodes to be ideal

(a)

D₁ is forward biased and D₂ is reverse biased and hence current flows from A to B.

(b)

D₂ is forward biased and D₁ is reverse biased and hence no current flows from B to A and vice versa.

(c)

D₁ and D₂are both forward biased and hence current flows from A to B.

(d)

D₁ and D₂ are both reverse biased and hence no current flows from A to B and vice versa

18.

A photodiode converts

(a)

variation in intensity of light into current amplitude variation

(b)

variation of current amplitude into variation in intensity of emitted light

(c)

variation of voltage into variation of current

(d)

variation of intensity of light into variation of volume

19.

The current through an ideal p-n junction shown in the following circuit diagram will be

(a)

zero

(b)

1 mA

(c)

10 mA

(d)

30 mA

20.

The diode shown in the circuit is a silicon diode. The potential difference between the points A and B will be

(a)

6 V

(b)

0.6 V

(c)

0.7 V

(d)

0 V

21.

Which is reverse biased diode?

(a)

(b)

(c)

(d)

22.

If reverse biasing potential is increased beyond a certain critical (breakdown) value, then

(a)

diode gets destroyed due to overheating

(b)

no current flows through the diode

(c)

after breakdown a heavy current flows from n to p side

(d)

potential barrier becomes zero

23.

Which of these graphs shows potential difference between p-side and n-side of a p-n Junction in equilibrium?

(a)

(b)

(c)

(d)

24.

The potential barrier of germanium diode is

(a)

0.1 V ,

(b)

0.3 V

(c)

0.5 V

(d)

0.7 V

25.

In an n-type silicon, which of the following statements is correct?

(a)

Electrons are majority charge carriers and trivalent atoms are the dopants

(b)

Electrons are minority charge carriers and pentavalent atoms are the dopants

(c)

Holes are minority charge carriers and pentavalent atoms are the dopants

(d)

Holes are majority charge carriers and trivalent atoms are the dopants

26.

The ratio of output frequencies of half wave rectifier and a full-wave rectifier, when an input of frequency 200 Hz is fed at input ?

(a)

1 :2

(b)

2:1

(c)

4:1

(d)

1:4

27.

A 220 V AC supply is connected between points A and B (figure). What will be the potential difference V across the capacitor?

(a)

220 V

(b)

110 V

(c)

0 V

(d)

\(220 \sqrt{2} \mathrm{~V}\)

28.

The substance which is doped in an intrinsic semiconductor to make p-type semiconductor is

(a)

phosphorus

(b)

antimony

(c)

aluminium

(d)

arsenic

29.

The lighting emitting diode(LED),

(a)

is made from the semiconducting compound gallium arsenide phosphide

(b)

emits light when forward biased

(c)

is made from one of the two basic semiconducting materials,silicon or germanium

(d)

emits light when reverse biased.

30.

Which of the following statements concerning the depletion zone of an unbiased p-n junction is (are) true?

(a)

The width of the zone is independent of the densities of the dopants(impurities)

(b)

The width of the zone is dependent on the densities of the dopants

(c)

The electric field in the zone is provided by the electrons in the conduction band and holes in the valence band

(d)

The electric field in the zone is produced by the ionized dopant atoms.

31.

For an intrisnsic semiconductor the staement/ statements that hold good are:

(a)

an intrinsic semiconductor is a perfect insulator at 0 K

(b)

the number of charge carriers varies with temperature in an exponential way.

(c)

the number density of electrons is always more than the number density of holes.

(d)

the mobility of electrons is more than that of holes.

32.

The electrical conductivity of pure silicon can be increased by

(a)

increasing the temperature

(b)

doping donor impurities

(c)

doping acceptor impurities

(d)

falling ultraviolet light on it

33.

The number of minority carriers crossing the junction of a diode depends primarily on the

(a)

concentration of doping impurities

(b)

imagnitude of potential barrier

(c)

magnitude of the forward bias voltage

(d)

rate of thermal generation of electron-hole pair

34.

The barrier potential of a p-n junction depends on :
(i) type of semiconductor material
(ii) amount of doping
(iii) temperature.
Which one of the following is correct?

(a)

(i) and (ii) only

(b)

(ii) only

(c)

(ii) and (iii) only

(d)

(i),(ii) and (iii)

35.

A \(p-n\) junction diode having potential difference 0.5 volt across its junction which does not depend on current, is connected in series with resistance of 20 \(\Omega \)across source. If 0.1 A current passes through resistance, then what is the voltage of the source.

(a)

1.5 V

(b)

2.0 V

(c)

2.5 V

(d)

5 V

36.

In n type semiconductor when all donor states are filled,then the net charge density in the donor states becomes

(a)

(b)

(c)

<1,but not zero

(d)

zero

37.

Pure Si at 500 k has equal number of electron \((n_{ e })\)and hole \((n_{ h })\)concentration of \(1.5\times10^{ 16 }m^{ -3 }\) Doping by indium increases \({ n }_{ h }\) to \(4.5\times10^{ 22 }m^{ -3 }\)

(a)

n - type with electron concentration \({ n }_{ e }=5\times10^{ 22 }m^{ -3 }\)

(b)

p-type with electron concentration \({ n }_{ e }=2.5\times10^{ 10 }m^{ -3 }\)

(c)

\(n-\)type with electron concentration \({ n }_{ e }=2.5\times10^{ 23 }m^{ -3 }\)

(d)

\(p-\) type having electron concentration \({ n }_{ e }=5\times10^{ 9 }m^{ -3 }\)

38.

A Ge specimen is doped with AI. The concentration of acceptor atoms is \(-10^{ 21 }\) atoms/\(m^{ 3 }\) , the concentration of electrons in the specimen is

(a)

\(10^{ 17 }/m^{ 3 }\)

(b)

\(10^{ 15 }/m^{ 3 }\)

(c)

\(10^{ 4 }/m^{ 3 }\)

(d)

\(10^{ 2 }/m^{ 3 }\)

39.

A semiconductor has an electron concentration \(8 \times 10^{ 13 }\ per\ m^{ 3 }\) and hole concentration of \(5\times10^{ 12 }\ per\ m^{ 3 }\). The semiconductor is

(a)

n - type

(b)

p - type

(c)

Intrinsic semiconductor

(d)

None of the above

40.

The energy gap between conduction band and valence band is of the order of 0.07 eV. It is a/an

(a)

insulator

(b)

conductor

(c)

semiconductor

(d)

alloy

41.

The resistance of an intrinsic semi-conductor when heated

(a)

increases

(b)

remains constant

(c)

decreases linearly

(d)

decreases exponentially

42.

The breakdown in a reverse biased p-n junction is more likely to occur due to

(a)

large velocity of the minority charge carriers if the doping concentration is small

(b)

large velocity of the minority charge carriers if the doping concentration is large

(c)

strong electric field in a depletion region if the doping concentration is small

(d)

strong electric field in the depletion region if the doping concentration is large

43.

In the depletion region of a diode

(a)

there are no mobile charges

(b)

equal number of holes and electrons exist, making the region neutral

(c)

recombination of holes and electrons has taken place

(d)

mmobile charged ions exist

44.

When an electric field is applied across a semiconductor

(a)

electrons move from lower energy level to higher energy level in the condition band

(b)

electrons move from higher energy level to lower energy level in the conduction band

(c)

holes in the valence band move from higher energy level to lower energy level

(d)

holes in the valence band move from lower energy level to higher energy level.

45.

Hole is

(a)

an anti-particle of electron

(b)

a vacancy created when an electron leaves a covalent bond

(c)

absence of free electron

(d)

an artificially created particle

46.

The conductivity of a semiconductor increases with increase in temperature because

(a)

number density of free current carriers increases

(b)

relaxation time increases

(c)

both number density of carriers and relaxation time increase

(d)

number density of carriers increases, relaxation time decreases but effect of decrease in relaxation time is much less than increase in number density

47.

When a forward bias is applied to p-n junctions it

(a)

raises the potential barrier

(b)

reduces the majority carrier to zero

(c)

lower the potential barrier

(d)

None of these

48.

In an unbiased p-n junction, holes diffuse from the p- region to n- region because

(a)

Free electrons in the n-region attract them

(b)

they move across the junction by the potential difference

(c)

hole concentration in p-region is more as compared to hole concentration in n-region

(d)

all the above

49.

Carbon, silicon and germanium have four valence electrons each, These are characterised by valence and conduction bands separated by energy bandgap respectively equal to \((E_{ g })_{ c, }({ E }_{ g })_{ si }\ and\ { (E }_{ g })_{ Ge }\)Which of the following statements is true?

(a)

\((E_{ g })_{ si, }<({ E }_{ g })_{ Ge }<\ { (E }_{ g })_{ C }\)

(b)

\((E_{ g })_{ C, }>({ E }_{ g })_{ si }>\ { (E }_{ g })_{ Ge }\)

(c)

\((E_{ g })_{ C, }=({ E }_{ g })_{ si }=\ { (E }_{ g })_{ Ge }\)

(d)

\((E_{ g })_{ C, }=({ E }_{ g })_{ si }=\ { (E }_{ g })_{ Ge }\)

50.

In n-type silicon, Which of the following statement is true:

(a)

Electrons are majority carriers and trivalent atoms are the dopants

(b)

Electrons are minority carriers and pentavalent atoms are the dopants

(c)

Holes are minority carriers and pentavalent atoms are the dopants

(d)

Holes are majority carriers and trivalent atoms are the dopants.

51.

The built in potential of p-n junction diode is a function of

(a)

temperature

(b)

biased voltage

(c)

doping density

(d)

all of the above

52.

The electrical resistance of depletion layer is large because

(a)

it has no charge carriers

(b)

it has few holes as charge carriers

(c)

it contains few electrons as charge carriers

(d)

it contains few ions as charge carriers

53.

In the middle of the depletion layer of a review biased p-n junction, the

(a)

electric field is zero

(b)

potential is zero

(c)

electric field is maximum

(d)

potential is maximum

54.

The reverse saturation of p-n junction

(a)

depends on doping concentration

(b)

depends on diffusion lengths of carriers

(c)

depends on the doping concentrations and diffusions lengths

(d)

depends on the doping concentartions, diffusion length and device temperature

55.

A semiconductor is cooled from \(T_{ 1 }K\ to\ T_{ 2 }k\) Its resistance will

(a)

decrease

(b)

increase

(c)

first decreases then increases

(d)

will not change

56.

Which type of semiconductor is obtained by mixing arsenic with silicon?

(a)

\(n-type\)

(b)

\(p-type\)

(c)

Both

(d)

None

57.

A p-type semiconductor is obtained by doping silicon with

(a)

germanium

(b)

gallium

(c)

bismuth

(d)

Phosphorus

58.

n - type semiconductor is obtained when

(a)

germanium is doped with arsenic

(b)

germanium is doped with indium

(c)

germanium is doped with aluminium

(d)

silicon is doped with indium

59.

In an n-type semiconductor, the Fermi level lies 0.3 e V below the conduction band at 300 k. If the temperature is increased to 330 k, where does the new position of the Fermi level lie?

(a)

0.55 e V below the conduction band

(b)

0.44 eV below the conduction band

(c)

0.33 eV below the conduction band

(d)

0.27 eV below the conduction band

60.

In intrinsic semiconductor at room temperature, the number of electrons and holes are

(a)

equal

(b)

zero

(c)

unequal

(d)

infinite

61.

In good conductorsof electricity the type of bonding that exists is

(a)

ionic

(b)

vander waals

(c)

covalent

(d)

metallic

62.

The conduction band in a solid is partially filled at 0 k. The solid sample is

(a)

Conductor

(b)

Semiconductor

(c)

Insulator

(d)

none of these

Assertion and reason

31 x 1 = 31

63.

Assertion (A): The depletion region in a p-n junction diode acts as an insulator.
Reason (R): The depletion region is created by the immobile ions, resulting in the absence of majority carriers and behaving like an insulator.
Codes:
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.

64.

Assertion (A): A p-n junction diode conducts current in the forward bias but not in the reverse bias.
Reason (R): In forward bias, the p-n junction allows the flow of majority carriers, facilitating current flow, while in reverse bias, the depletion region widens, preventing current flow.
Codes:
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.

65.

Assertion (A): In an N-type semiconductor, the majority of carriers are electrons.
Reason (R): N-type semiconductors are doped with pentavalent impurities that provide extra electrons for conduction.
Codes:
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.

66.

Assertion : The diffusion current in a p-n junction is from the p-side to the n-side.
Reason : The diffusion current in a p-n junction is greater than the drift current when the junction is in forward biased.
Codes:
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.

67.

Assertion (A) : In a semiconductor diode, the reverse biased current is due to drift of free electrons and holes.
Reason (R) : The drift of electrons and holes is due to thermal excitations.
Codes:
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.

68.

Assertion (A) : The ratio of free electrons to holes in intrinsic semiconductor is greater than one.
Reason (R) : The electrons are lighter particles and holes are heavy particles.
Codes:
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.

69.

Assertion (A) : The half-wave rectifier work only for positive half cycle of ac.
Reason (R) : In half-wave rectifier only one diode is used.
Codes:
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.

70.

Assertion (A) : The direction of diffusion current in a junction diode is from n-region to p-region.
Reason (R) :The majority current carriers diffuse from a region of lower concentration to a region of higher concentration.
Codes:
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.

71.

Assertion (A) : The resistance of p-n junction is low when forward biased and is high when reverse biased.
Reason (R) : In reversed biased, the depletion layer is reduced.
Codes:
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.

72.

Assertion (A) : p-n junction diode can be used even at ultra high frequencies.
Reason (R) : Capacitative reactance of a p-n junction diode increases as frequency increases.
Codes:
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.

73.

Assertion (A) : The conductivity of a semiconductor increases with rise of temperature.
Reason (R) : On rising temperature covalent bonds of semiconductor breaks.
Codes:
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.

74.

Assertion : The drift current in a p-n junction is from the n-side to the p-side.
Reason : It is due to free electrons only.
Codes:
(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.

75.

Assertion : When two semi conductor of p and n type are brought in contact, they form p-n junction which act like a rectifier.
Reason : A rectifier is used to convent alternating current into direct current.
Codes:
(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.

76.

Assertion : The number of electrons in a p-type silicon semiconductor is less than the number of electrons in a pure silicon semiconductor at room temperature.
Reason : It is due to law of mass action.
Codes:
(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.

77.

Assertion : Electron has higher mobility than hole in a semiconductor.
Reason : The mass of electron is less than the mass of the hole.
Codes:
(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.

78.

Assertion : Silicon is preferred over germanium for making semiconductor devices.
Reason : The energy gap in germanium is more than the energy gap in silicon.
Codes:
(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.

79.

Assertion : A p-type semiconductors is a positive type crystal.
Reason : A p- type semiconductor is an uncharged crystal.
Codes:
(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.

80.

Assertion : In semiconductors, thermal collisions are responsible for taking a valence electron to the conduction band.
Reason : The number of conduction electrons go on increasing with time as thermal collisions continuously take place.
Codes:
(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.

81.

Assertion : If the temperature of a semiconductor is increased then its resistance decreases.
Reason : The energy gap between conduction band and valence band is very small.
Codes:
(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.

82.

Assertion : A pure semiconductor has negative temperature coefficient of resistance.
Reason : In a semiconductor on raising the temperature, more charge carriers are released, conductance increases and resistance decreases.
Codes:
(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
(c) If the Assertion is correct but Reason is incorrect.
(d) If both the Assertion and Reason are incorrect.

83.

Assertion (A) A rectifier converts as alternating curent into a direct curent.
Reason (R) A p-n junction diode can work as a rectifier.
(a) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) Assertion is true but Reason is false.
(d) Assertion is false but Reason is true.

84.

Assertion (A) The electrical conductivity of a semiconductor increases on doping.
Reason (R) Doping always increases the number of electrons in the semiconductor.
(a) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) Assertion is true but Reason is false.
(d) Assertion is false but Reason is true.

85.

Assertion (A) The resistivity of a semiconductor decreases with temperature.
Reason (R) The atoms of a semiconductor vibrate with larger amplitudes of higher temperatures thereby increasing its resistivity.
(a) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) Assertion is true but Reason is false.
(d) Assertion is false but Reason is true.

86.

Assertion (A) The conductivity of an intrinsic semiconductor depends on its temperature.
Reason (R) The conductivity of an intrinsic semiconductor is slightly higher than that of a lightly doped p-type semiconductor.
(a) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(b) Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
(c) Assertion is true but Reason is false.
(d) Assertion is false but Reason is true.

87.

Asseetion (A) : The half-wave rectifier work only for positive half cycle of ac.
Reason (R) : In half-wave rectifier only one diode is used.
Codes:
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is NOT the correct explanation of A
(c) A is true but R is false
(d) A is false and R is also false

88.

Assertion (A) : V - I characteristic of p-n diode is same as that of any other conductor.
Reason (R) : p-n diode behave as conductor at room temperature.
Codes:
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is NOT the correct explanation of A
(c) A is true but R is false
(d) A is false and R is also false

89.

Assertion (A) : The resistivity of a semiconductor increases with temperature.
Reason (R) : The atoms of a semiconductor vibrate with larger amplitude at higher temperatures thereby increasing its resistivity.
Codes:
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is NOT the correct explanation of A
(c) A is true but R is false
(d) A is false and R is also false

90.

Assertion (A) : At 0 K, Germanium is a superconductor.
Reason (R) : At 0 K, Germanium offers zero resistance.
Codes:
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is NOT the correct explanation of A
(c) A is true but R is false
(d) A is false and R is also false

91.

Assertion (A) : At absolute zero the conductivity of semiconductor is zero.
Reason (R) : In a semiconductor there are no free electrons at any temperature.
Codes:
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is NOT the correct explanation of A
(c) A is true but R is false
(d) A is false and R is also false

92.

Assertion (A) : Diamond behaves like an insulator.
Reason (R) : There is a large energy gap between valence band and conduction band of diamond.
Codes:
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is NOT the correct explanation of A
(c) A is true but R is false
(d) A is false and R is also false

93.

Assertion (A) : The depletion layer in the p-n junction is free from mobile charge carriers.
Reason (R) : There is no electric field across the junction barrier.
Codes:
(a) Both A and R are true and R is the correct explanation of A
(b) Both A and R are true but R is NOT the correct explanation of A
(c) A is true but R is false
(d) A is false and R is also false

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Answers Key:

Multiple Choice Question

62 x 1 = 62

(d)
diffusion current remains almost constant but drift current increases till both currents-become equal

(b)
diffusion of the electrons and holes

(b)
0.25 Ω

(b)
5/50 A

(a)
0.2 A

(b)
absence of one electron

10.

(b)
gallium to pure silicon

11.

(b)
2.3 V

12.

(b)
B, D

13.

14.

(b)
EG₁ < EG₂ < EG₃

15.

(b)
increases with the rise in its temperature

16.

17.

(b)
D₂ is forward biased and D₁ is reverse biased and hence no current flows from B to A and vice versa.

18.

(a)
variation in intensity of light into current amplitude variation

19.

(a)
zero

20.

(a)
6 V

21.

22.

23.

24.

(b)
0.3 V

25.

26.

(a)
1 :2

27.

(d)
\(220 \sqrt{2} \mathrm{~V}\)

28.

29.

(a)
is made from the semiconducting compound gallium arsenide phosphide

30.

(a)
The width of the zone is independent of the densities of the dopants(impurities)

31.

(b)
the number of charge carriers varies with temperature in an exponential way.

32.

(a)
increasing the temperature

33.

(d)
rate of thermal generation of electron-hole pair

34.

(d)
(i),(ii) and (iii)

35.

36.

(b)
>1

37.

(d)
\(p-\) type having electron concentration \({ n }_{ e }=5\times10^{ 9 }m^{ -3 }\)

38.

(a)
\(10^{ 17 }/m^{ 3 }\)

39.

(a)
n - type

40.

(b)
conductor

41.

(d)
decreases exponentially

42.

(a)
large velocity of the minority charge carriers if the doping concentration is small

43.

(a)
there are no mobile charges

44.

(a)
electrons move from lower energy level to higher energy level in the condition band

45.

(b)
a vacancy created when an electron leaves a covalent bond

46.

(d)
number density of carriers increases, relaxation time decreases but effect of decrease in relaxation time is much less than increase in number density

47.

(b)
reduces the majority carrier to zero

48.

49.

(b)
\((E_{ g })_{ C, }>({ E }_{ g })_{ si }>\ { (E }_{ g })_{ Ge }\)

50.

51.

(d)
all of the above

52.

(a)
it has no charge carriers

53.

(a)
electric field is zero

54.

(d)
depends on the doping concentartions, diffusion length and device temperature

55.

(b)
increase

56.

57.

(b)
gallium

58.

(a)
germanium is doped with arsenic

59.

(d)
0.27 eV below the conduction band

60.

equal

61.

(d)
metallic

62.

Conductor

Assertion and reason

31 x 1 = 31

63.

(a) Both A and R are true and R is the correct explanation of A.

64.

(a) Both A and R are true and R is the correct explanation of A.

65.

(a) Both A and R are true and R is the correct explanation of A.

66.

(b) Both A and R are true but R is not the correct explanation of A.

67.

(b) Both A and R are true but R is not the correct explanation of A.

68.

(b) Both A and R are true but R is not the correct explanation of A.

69.

(a) Both A and R are true and R is the correct explanation of A.

70.

(d) A is false and R is also false.

71.

72.

73.

74.

(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.

75.

(b) If both Assertion and Reason are correct but Reason is not a correct explanation of the Assertion.
Explanation:
Study of junction diode characteristics shows that the junction diode offers a low resistance path, when forward biased and high resistance path when reverse biased. This feature of the junction diode enables it to be used as a rectifier.

76.

(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.

77.

(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.

78.

(c) If the Assertion is correct but Reason is incorrect.
Explanation:
Silicon is cheaper than germanium, so it is preferred over germanium. But energy gap in germanium is smaller than silicon.

79.

(d) If both the Assertion and Reason are incorrect.
Explanation:
There is no charge on P-type semiconductor, because each atom of semiconductor is itself neutral.

80.

81.

(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
Explanation:
In semiconductors the energy gap between conduction band and valence band is small (1 eV). Due to temperature rise, electron in the valence band gain thermal energy and may jumpy across the small energy gap, (to the conduction band). Thus conductivity increases and hence resistance decreases.

82.

(a) If both Assertion and Reason are correct and the Reason is a correct explanation of the Assertion.
Explanation:
In semiconductors, by increasing temperature, covalent bond breaks and conduction hole and electrons increase.

83.

84.

(a) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

85.

(c) Resistivity of a semiconductor decreases with the temperature. The atoms of a semiconductor vibrate with larger amplitudes at higher temperature thereby increasing its conductivity not resistivity.

86.

87.

(a): In half wave rectifier, the one diode is biased only when ac is in positive half of its cycle.For negative half of the ac cycle the diode is reversed biased and there is no output corresponding to that. Since for only one-half cycle we get a voltage output,because of which it is called half wave rectifier.

88.

(d) : The V-I characteristic of p-n diode depends whether the junction is forward biased or reverse biased. This can be showed by graph between voltage and current.

In the given graph knee voltage is a voltage at which forward bias becomes greater than the potential barrier, the forward current increases almost linearly, where as zener voltage is a voltage at which reverse current increases suddenly. From this graph we can verify that p-n diode characteristics are very different from that of conductor which obey's Ohm's law.

89.

(d) : With the increase of temperature, the average energy exchanged in a collision increases and so more valence electrons can cross the energy gap, thereby increasing the electron-hole pairs. As in a semiconductor, conduction occurs mainly through electron-hole pairs, so conductivity increases with increase of temperature. Which in turn implies that the resistivity of a semiconductor decreases with rise in temperature.

90.

(d) : At 0 K, Germanium offers infinite resistance, and it behaves as an insulator

91.

(c): In a semiconductor, there are no free electrons at 0 K. The number of free electrons increases with increase in temperature because with increase in temperature the electron get sufficient energy to cross forbidden band and reach conduction band. But total number of free electrons in a semiconductor is less than that in a conductor.

92.

(a): In insulator, the forbidden energy gap is quite large. When electric field is applied to such a solid, the electron find it difficult to acquire such a large amount of energy. Thus no electron flow occurs.

93.

(c): Due to diffusion of holes from the p-region to the n-region and of electrons from the n-region to the p-region an electric field is set up across the junction barrier. Once the depletion layer is formed it is in equilibrium and becomes free of mobile charge carriers.