CBSE Class 12 Physics Semiconductor Devices Worksheet Set A

1. Distinction of metals, semiconductor and insulator on the basis of Energy band of Solids.

2. Types of Semiconductor.

3. PN Junction formation

4. Diode characteristics.

5. Diode as a rectifier

6. Symbol and sections of transistor.

7. Transistor as an Amplifier.

8. Basic logic gates.

Energy Bands of Solids

1. Energy Band In a crystal due to interatomic interaction valence electrons of one atom are shared by more than one atom in the crystal. Now splitting of energy levels takes place. The collection of these closely spaced energy levels is called an energy band.

2. Valence Band This energy band contains valence electrons. This band may be Partially or completely filled with electrons but never be empty. The electrons in this band are not capable of gaining energy from external electric field to take part in conduction of current.

3. Conduction Band This band contains conduction electrons. This band is either empty or Partially filled with electrons. Electrons present in this band take part in the conduction of current.

4. Forbidden Band This band is completely empty. The minimum energy required to shift an electron from valence band to conduction band is called band gap (Eg). 

Types of Semiconductor

(i) Intrinsic Semiconductor: A semiconductor in its pure state is called intrinsic semiconductor.

(ii) Extrinsic Semiconductor: A semiconductor doped with suitable impurity to increase its conductivity, is called extrinsic semiconductor. 

Important Questions for NCERT Class 12 Physics Semiconductor Devices

Question. When using a triode, as an amplifier, the electrons are emitted by
(a) grid and collected by cathode only
(b) cathode and collected by the anode only
(c) anode and collected by cathode only
(d) anode and collected by the grid and by cathode.

Answer: B

Question. For amplification by a triode, the signal to be amplified is given to
(a) the cathode
(b) the grid
(c) the glass envelope
(d) the anode 

Answer: B

Question. For an electronic valve, the plate current I and plate voltage V in the space charge limited region are related as
(a) I is proportional to V 3/2
(b) I is proportional to V 2/3
(c) I is proportional to V
(d) I is proportional to V 2 

Answer: A

Question. When a triode is used as an amplifier the phase difference between the input signal voltage and the output is
(a) 0
(b) p
(c) p/2
(d) p/4.

Answer: B

Question. Choose the only false statement from the following.
(a) In conductors the valence and conduction bands overlap.
(b) Substances with energy gap of the order of 10 eV are insulators.
(c) The resistivity of a semiconductor increases with increase in temperature.
(d) The conductivity of a semiconductor increases with increase in temperature. 

Answer: C

Question. Carbon, silicon and germanium atoms have four valence electrons each. Their valence and conduction bands are separated by energy band gaps represented by (Eg)C, (Eg)Si and (Eg)Ge respectively.
Which one of the following relationships is true in their case?
(a) (Eg)C > (Eg)Si
(b) (Eg)C < (Eg)Si
(c) (Eg)C = (Eg)Si
(d) (Eg)C < (Eg)Ge 

Answer: A

Question. In semiconductors at a room temperature
(a) the valence band is partially empty and the conduction band is partially filled
(b) the valence band is completely filled and the conduction band is partially filled
(c) the valence band is completely filled
(d) the conduction band is completely empty.

Answer: A

Question. C and Si both have same lattice structure; having 4 bonding electrons in each. However, C is insulator whereas Si is intrinsic semiconductor. This is because
(a) in case of C the valence band is not completely filled at absolute zero temperature
(b) in case of C the conduction band is partly filled even at absolute zero temperature
(c) the four bonding electrons in the case of C lie in the second orbit, whereas in the case of Si they lie in the third
(d) the four bonding electrons in the case of C lie in the third orbit, whereas for Si they lie in the fourth orbit. 

Answer: C

Question. At absolute zero, Si acts as
(a) non metal
(b) metal
(c) insulator
(d) none of these.

Answer: C

Question. For a p-type semiconductor, which of the following statements is true?
(a) Electrons are the majority carriers and pentavalent atoms are the dopants.
(b) Electrons are the majority carriers and trivalent atoms are the dopants.
(c) Holes are the majority carriers and trivalent atoms are the dopants.
(d) Holes are the majority carriers and pentavalent atoms are the dopants. 

Answer: C

Question. In a n-type semiconductor, which of the following statement is true?
(a) Holes are minority carriers and pentavalent atoms are dopants.
(b) Holes are majority carriers and trivalent atoms are dopants.
(c) Electrons are majority carriers and trivalent atoms are dopants.
(d) Electrons are minority carriers and pentavalent atoms are dopants. 

Answer: A

Question. If a small amount of antimony is added to germanium crystal
(a) it becomes a p-type semiconductor
(b) the antimony becomes an acceptor atom
(c) there will be more free electrons than holes in the semiconductor
(d) its resistance is increased.

Answer: C

Question. In a p type semiconductor, the majority carriers of current are
(a) protons
(b) electrons
(c) holes
(d) neutrons 

Answer: C

Question. Which of the following, when added as an impurity into the silicon produces n type semiconductor?
(a) B
(b) Al
(c) P
(d) Mg 

Answer: C

Question. To obtain a p-type germanium semiconductor, it must be doped with
(a) indium
(b) phosphorus
(c) arsenic
(d) antimony. 

Answer: A

Question. Copper has face centered cubic (fcc) lattice with interatomic spacing equal to 2.54 Å. The value of lattice constant for this lattice is
(a) 2.54 Å
(b) 3.59 Å
(c) 1.27 Å
(d) 5.08 Å. 

Answer: B 

Question. In an unbiased p-n junction, holes diffuse from the p-region to n-region because of
(a) he attraction of free electrons of n-region
(b) the higher hole concentration in p-region than that in n-region
(c) the higher concentration of electrons in the n-region than that in the p-region
(d) the potential difference across the p-n junction.

Answer: B

Question. When n-P-n transistor is used as an amplifier, then
(a) electrons move from collector to emitter
(b) electrons move from emitter to collector
(c) electrons move from collector to base
(d) holes move from emitter to collector

Answer: B

Question. In a semiconductor diode, the barrier potential offers opposition to
(a) holes in P-region only
(b) free electrons in N-region only
(c) majority carriers in both regions
(d) majority as well as minority carriers in both regions

Answer: C

Question. If the forward voltage in a semiconductor diode is changed from 0.5V to 0.7 V, then the forward current changes by 1.0 mA. The forward resistance of diode junction will be
(a) 100 Ω
(b) 120 Ω
(c) 200 Ω
(d) 240 Ω

Answer: C

Question. In a CE transistor amplifier, the audio signal voltage across the collector resistance of 2kΩ is 2V. If the base resistance is 1kΩ and the current amplification of the transistor is 100, the input signal voltage is
(a) 0.1 V
(b) 1.0 V
(c) 1 mV
(d) 10 mV

Answer: D

Question. Application of a forward bias to a p–n junction
(a) widens the depletion zone.
(b) increases the potential difference across the depletion zone
(c) increases the number of donors on the n side.
(d) increases the electric field in the depletion zone.

Answer: C

Question. The device that can act as a complete electronic circuit is
(a) junction diode
(b) integrated circuit
(c) junction transistor
(d) zener diode

Answer: B

Question. For a common base amplifier, the values of resistance gain and voltage gain are 3000 and 2800 respectively. The current gain will be
(a) 1.1
(b) 0.98
(c) 0.93
(d) 0.83

Answer: C

Question. In the case of a common emitter transistor amplifier the ratio of the collector current to the emitter current I_c /I_e is 0.96. The current gain of the amplifier is
(a) 6
(b) 48
(c) 24
(d) 12

Answer: C

Question. Which of the following is unipolar transistor?
(a) p – n – p transistor
(b) n – p – n transistor
(c) Field effect transistor
(d) Point contact transistor

Answer: C

Question. In common emitter amplifier the I_c/I_e is 0.98. The current gain will be
(a) 4.9
(b) 7.8
(c) 49
(d) 78

Answer: C

Question. When the forward bias voltage of a diode is changed from 0.6 V to 0.7 V, the current changes from 5 mA to 15 mA. Then its forward bias resistance is
(a) 0.01 Ω
(b) 0.1 Ω
(c) 10 Ω
(d) 100 Ω

Answer: C

Question. Truth table for the given circuit is

Answer: C

Question. The gate for which output is high if atleast one input is low?
(a) NAND
(b) NOR
(c) AND
(d) OR

Answer: A

Question. Radiowaves of constant amplitude can be generated with
(a) FET
(b) filter
(c) rectifier
(d) oscillator

Answer: D

Question. The current gain β may be defined as
(a) the ratio of change in collector current to the change in emitter current for a constant collector voltage in a common base arrangement.
(b) the ratio of change in collector current to the change in the base current at constant collector voltage in a common emitter circuit
(c) the ratio of change in emitter current to the change in base current for constant emitter voltage in common emitter circuit.
(d) the ratio of change in base current to the change in collector current at constant collector voltage in common emitter circuit.

Answer: B

Question. Current gain of a transistor in common base mode is 0.95. Its value in common emitter mode is
(a) 0.95
(b) 1.5
(c) 19
(d) (19)^–1

Answer: C

Question. The intrinsic conductivity of germanium at 27° is 2.13 mho m^–1 and mobilities of electrons and holes are 0.38 and 0.18 m²V^–1s^–1 respectively. The density of charge carriers is
(a) 2.37 × 10¹⁹ m^–3
(b) 3.28 × 10¹⁹ m^–3
(c) 7.83 × 10¹⁹ m^–3
(d) 8.47 × 10¹⁹ m^–3

Answer: A

Question. An oscillator is nothing but an amplifier with
(a) positive feedback
(b) large gain
(c) no feedback
(d) negative feedback

Answer: A

Question. The grid voltage of any triode valve is changed from –1 volt to –3 volt and the mutual conductance is 3 × 10^–4 mho. The change in plate circuit current will be
(a) 0.8 mA
(b) 0.6 mA
(c) 0.4 mA
(d) 1 mA

Answer: B

Question. A semi-conducting device is connected in a series circuit with a battery and a 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 be
(a) a p-n junction
(b) an intrinsic semi-conductor
(c) a p-type semi-conductor
(d) an n-type semi-conductor

Answer: A

Important Questions for NCERT Class 12 Physics Semiconductor Devices

Question. When arsenic is added as an impurity to silicon, the resulting material is
(a) n-type conductor
(b) n-type semiconductor
(c) p-type semiconductor
(d) none of these. 

Answer: B

Question. When n type semiconductor is heated
(a) number of electrons increases while that of holes decreases
(b) number of holes increases while that of electrons decreases
(c) number of electrons and holes remain same
(d) number of electrons and holes increases equally.

Answer: D

Question. The increase in the width of the depletion region in a p-n junction diode is due to
(a) forward bias only
(b) reverse bias only
(c) both forward bias and reverse bias
(d) increase in forward current 

Answer: B

Question. The barrier potential of a p-n junction depends on
(1) type of semiconductor material
(2) amount of doping
(3) temperature
Which one of the following is correct?
(a) (1) and (2) only
(b) (2) only
(c) (2) and (3) only
(d) (1), (2) and (3)

Answer: D

Question. In an unbiased p-n junction, holes diffuse from the p-region to n-region because of
(a) he attraction of free electrons of n-region
(b) the higher hole concentration in p-region than that in n-region
(c) the higher concentration of electrons in the n-region than that in the p-region
(d) the potential difference across the p-n junction.

Answer: B

Question. In a p-n junction
(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. 

Answer: A

Question. Depletion layer consists of
(a) mobile ions
(b) protons
(c) electrons
(d) immobile ions 

Answer: D

Question. The depletion layer in the p-n junction region is caused by
(a) drift of holes
(b) diffusion of charge carriers
(c) migration of impurity ions
(d) drift of electrons.

Answer: B

Question. In a p-n junction diode, change in temperature due to heating
(a) affects only reverse resistance
(b) affects only forward resistance
(c) does not affect resistance of p-n junction
(d) affects the overall V - I characteristics of p-n junction.

Answer: D

Question. In forward biasing of the p-n junction
(a) the positive terminal of the battery is connected to p-side and the depletion region becomes thick.
(b) the positive terminal of the battery is connected to n-side and the depletion region becomes thin.
(c) the positive terminal of the battery is connected to n-side and the depletion region becomes thick.
(d) the positive terminal of the battery is connected to p-side and the depletion region becomes thin.

Answer: D

Question. Application of a forward bias to a p-n junction
(a) widens the depletion zone
(b) increases the potential difference across the depletion zone
(c) increases the number of donors on the n side
(d) decreases the electric field in the depletion zone.

Answer: D

Question. Reverse bias applied to a junction diode
(a) lowers the potential barrier
(b) raises the potential barrier
(c) increases the majority carrier current
(d) increases the minority carrier current 

Answer: B

Question. Barrier potential of a p-n junction diode does not depend on
(a) diode design
(b) temperature
(c) forward bias
(d) doping density

Answer: A

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

Answer: B

Question. In a junction diode, the holes are due to
(a) extra electrons
(b) neutrons
(c) protons
(d) missing of electrons

Answer: D

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

Answer: B

Question. A p-n photodiode is fabricated from a semiconductor with a band gap of 2.5 eV. It can detect a signal of wavelength
(a) 4000 nm
(b) 6000 nm
(c) 4000 Å
(d) 6000 Å 

Answer: C

Question. Which of the following gates will have an output of 1? 

(a) D
(b) A
(c) B
(d) C

Answer: D

Question. Application of a forward bias to a p–n junction
(a) widens the depletion zone
(b) increases the potential difference across the depletion zone
(c) increases the number of donors on the n side
(d) increases the electric field in the depletion zone.

Answer: C

Question. In Boolean algebra, Y = A + B implies that
(a) output Y exists when both inputs A and B exist
(b) output Y exists when either input A exists or input B exists or both inputs A and B exist
(c) output Y exists when either input A exists or input B exists but not when both inputs A and B exist
(d) output Y exists when both inputs A and B exists but not when either input A or B exist

Answer: B 

Question. Metallic solids are always opaque because
(a) they reflect all the incident light.
(b) they scatter all the incident light.
(c) the incident light is readily absorbed by the free electrons in a metal.
(d) the energy band traps the incident.

Answer: C

Question. Assuming that the silicon diode having resistance of 20 Ω , the current through the diode is (knee voltage 0.7 V) 

(a) 0 mA
(b) 10 mA
(c) 6.5 mA
(d) 13.5 mA

Answer: C

Question. Which one of the following represents forward bias diode? 

Answer: D

Question. Copper has face centered cubic (fcc) lattice with interatomic spacing equal to 2.54 Å. The value of lattice constant for this lattice is
(a) 2.54 Å
(b) 3.59 Å
(c) 1.27 Å
(d) 5.08 Å

Answer: B

Question. The ratio of work function and temperature of two emitters are 1 : 2, then the ratio of current densities obtained by them will be
(a) 4 : 1
(b) 2 : 1
(c) 1 : 2
(d) 1 : 4

Answer: D

Question. Minority carriers in a p-type semiconductor are
(a) free electrons
(b) holes
(c) neither holes nor free electron
(d) both holes and free electrons.

Answer: A

Question. The intrinsic semi conductor becomes an insulator at
(a) 0ºC
(b) 0 K
(c) 300 K
(d) –100ºC

Answer: B

Question. The transfer ratio b of transistor is 50. The input resistance of a transistor when used in C.E. (Common Emitter) configuration is 1kW. The peak value of the collector A.C current for an A.C input voltage of 0.01V peak is
(a) 100 mA
(b) .01 mA
(c) .25 mA
(d) 500 mA

Answer: D

Question. For transistor action
(1) Base, emitter and collector regions should have similar size and doping concentrations.
(2) The base region must be very thin and lightly doped.
(3) The eimtter-base junction is forward biased and basecollector junction is reverse based.
(4) Both the emitter-base junction as well as the basecollector junction are forward biased.
(a) (3) and (4)
(b) (4) and (1)
(c) (1) and (2)
(d) (2) and (3)

Answer: D

Question. A solid that is not transparent to visible light and whose electrical conductivity increases with temperature is formed by
(a) ionic binding
(b) covalent binding
(c) metallic binding
(d) vander Waal’s binding

Answer: B

Question. In a transistor, the change in base current from 100 μA to 125 μA causes a change in collector current from 5 mA to 7.5 mA, keeping collector-to-emitter voltage constant at 10 V. What is the current gain of the transistor?
(a) 200
(b) 100
(c) 50
(d) 25.

Answer: B

Question. NAND and NOR gates are called universal gates primarily because they
(a) are available universally
(b) can be combined to produce OR, AND and NOT gates
(c) are widely used in Integrated circuit packages
(d) are easiest to manufacture

Answer: B

Question. The following configuration of gate is equivalent to
(a) NAND gate
(b) XOR gate
(c) OR gate
(d) NOR gate

Answer: B

Question. Two junction diodes one of Germanium (Ge) and other of silicon (Si) are connected as shown in figure to a battery of emf 12 V and a load resistance 10 k Ω. The germanium diode conducts at 0.3 V and silicon diode at 0.7 V. When a current flows in the circuit, the potential of terminal Y will be 

(a) 12 V
(b) 11 V
(c) 11.3 V
(d) 11.7 V

Answer: D

Question. If the ratio of the concentration of electrons to that of holes in a semiconductor is 7/5 and the ratio of currents is 7/4 , then what is the ratio of their drift velocities?
(a) 5/8
(b) 4/5
(c) 5/4
(d) 4/7

Answer: C

Question. The circuit has two oppositively connected ideal diodes in parallel. What is the current flowing in the circuit?
(a) 1.71 A
(b) 2.00 A
(c) 2.31 A
(d) 1.33 A

Answer: B

Question. In figure given below, 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 D₂ are 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 

Answer: B

Important Questions for NCERT Class 12 Physics Semiconductor Devices

Question. The following figure shows a logic gate circuit with two inputs A and B and the output Y. The voltage waveforms of A, B and Y are given 

The logic gate is :
(a) NAND gate
(b) NOR gate
(c) OR gate
(d) AND gate

Answer: A

Question. In a junction diode, the holes are due to
(a) protons
(b) extra electrons
(c) neutrons
(d) missing electrons

Answer: D

Question. In a n-type semiconductor, which of the following statement is true?
(a) Electrons are minority carriers and pentavalent atoms are dopants.
(b) Holes are minority carriers and pentavalent atoms are dopants.
(c) Holes are majority carriers and trivalent atoms are dopants.
(d) Electrons are majority carriers and trivalent atoms are dopants.

Answer: B

Question. In figure given below V₀ is the potential barrier across a p–n junction, when no battary is connected across the junction 

(a) 1 and 3 both correspond to forward bias of junction
(b) 3 corresponds to forward bias of junction and 1 corresponds to reverse bias of junctions
(c) 1 corresponds to forward bias and 3 corresponds to reverse bias of junction
(d) 3 and 1 both correspond to reverse bias of junction

Answer: B

Question. A n-p-n transistor conducts when
(a) both collector and emitter are negative with respect to the base
(b) both collector and emitter are positive with respect to the base
(c) collector is positive and emitter is negative with respect to the base
(d) collector is positive and emitter is at same potential as the base

Answer: C

Question. A TV tower has a height of 100 m. How much population is covered by the TV broadcast if the average population density around the tower is 1000 km^–2 ? (radius of the earth = 6.37 × 10⁶ m)
(a) 4 lakh
(b) 4 billion
(c) 40,000
(d) 40 lakh

Answer: D

Question. In a bridge rectifier, the number of diodes required is
(a) 1
(b) 2
(c) 3
(d) 4

Answer: D

Question. Following diagram performs the logic function of 

(a) XOR gate
(b) AND gate
(c) NAND gate
(d) OR gate

Answer: B

Question. In the study of transistor as amplifier, if α = I_C/I_E , where, I_C, I_B and I_E are the collector, base and emitter currents, then
(a) β = (1+α)/α
(b) β = (1-α)/α
(c) β = α/(1-α)
(d) β = α/(1+α)

Answer: C

Question. 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 2V

Answer: D

Question. The ratio of forward biased to reverse biased resistance for pn junction diode is
(a) 10^–1 : 1
(b) 10^–2 : 1
(c) 10⁴ : 1
(d) 10^–4 : 1

Answer: D

Question. Hole in semiconductor is
(a) an anti – particle of electron
(b) a vacancy created when an electron leaves a covalent bond
(c) absence of free electrons
(d) an artificially created particle

Answer: B

Question. In germanium the energy gap is about 0.75 eV. The wavelength of light which germanium starts absorbing is
(a) 5000 Å
(b) 1650 Å
(c) 16500 Å
(d) 165000 Å

Answer: C

Question. Transfer characteristics [output voltage (V₀) vs input voltage (V₁)] for a base biased transistor in CE configuration is as shown in the figure. For using transistor as a switch, it is used

(a) in region (III)
(b) both in region (I) and (III)
(c) in region (II)
(d) in region (I)

Answer: B

Question. In a n-type semiconductor, which of the following statements is true? 
(a) Electrons are minority carriers and pentavalent atoms are dopants.
(b) Holes are minority carriers and pentavalent atoms are dopants.
(c) Holes are majority carriers and trivalent atoms are dopants.
(d) Electrons are majority carriers and trivalent atoms are dopants.

Answer: B

Question. The energy gap of silicon is 1.14 eV. The maximum wavelength at which silicon starts energy absorption, will be (h = 6.62 × 10^–34 Js ; c = 3 × 10⁸ m/s)
(a) 10.888 Å
(b) 108.88 Å
(c) 1088.8 Å
(d) 10888 Å

Answer: A

Question. A zener diode, having breakdown voltage equal to 15V, is used in a voltage regulator circuit shown in figure. The current through the diode is
(a) 10 mA
(b) 15 mA
(c) 20 mA
(d) 5 mA

Answer: D

Question. One way in which the operation of a n-p-n transistor differs from that of a p-n-p 
(a) the emitter junction is reversed biased in n-p-n
(b) the emitter junction injects minority carriers into the base region of the p-n-p
(c) the emitter injects holes into the base of the p-n-p and electrons into the base region of n-p-n
(d) the emitter injects holes into the base of n-p-n

Answer: C

Question. The output from a NAND gate is divided into two in parallel and fed to another NAND gate. The resulting gate is a
(a) NOT gate
(b) AND gate
(c) NOR gate
(d) OR gate

Answer: B

Question. The given graph represents V - I characteristic for a semiconductor device. Which of the following statement is correct ?
(a) It is V - I characteristic for solar cell where, point A represents open circuit voltage and point B short circuit current.
(b) It is a for a solar cell and point A and B represent open circuit voltage and current, respectively.
(c) It is for a photodiode and points A and B represent open circuit voltage and current, respectively.
(d) It is for a LED and points A and B represent open circuit voltage and short circuit current, respectively.

Answer: A

Question. The barrier potential of a p-n junction depends on: 
(A) type of semi conductor material
(B) amount of doping
(C) temperature
Which one of the following is correct ?
(a) (A) and (B) only
(b) (B) only
(c) (B) and (C) only
(d) (A), (B) and (C)

Answer: D

Question. The cause of the potential barrier in a p-n junction diode is
(a) depletion of negative charges near the junction
(b) concentration of positive charges near the junction
(c) depletion of positive charges near the junction
(d) concentration of positive and negative charges near the junction. 

Answer: D

Question. A semiconducting device is connected in a series circuit with a battery and a 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 be
(a) a p-type semiconductor
(b) an intrinsic semiconductor
(c) a p-n junction
(d) an n-type semiconductor.

Answer: C

Question. If a full wave rectifier circuit is operating from 50 Hz mains, the fundamental frequency in the ripple will be
(a) 25 Hz
(b) 50 Hz
(c) 70.7 Hz
(d) 100 Hz 

Answer: D

Question. A p-n junction diode can be used as
(a) condenser
(b) regulator
(c) amplifier
(d) rectifier

Answer: D

Question. An LED is constructed from a p-n junction diode using GaAsP. The energy gap is 1.9 eV. The wavelength of the light emitted will be equal to
(a) 10.4 × 10^–26 m
(b) 654 nm
(c) 654 Å
(d) 654 × 10^–11 m

Answer: B

Question. A p-n photodiode is fabricated from a semiconductor with a band gap of 2.5 eV. It can detect a signal of wavelength
(a) 4000 nm
(b) 6000 nm
(c) 4000 Å
(d) 6000 Å 

Answer: C

Question. A p-n photodiode is made of a material with a band gap of 2.0 eV. The minimum frequency of the radiation that can be absorbed by the material is nearly
(a) 1 × 1014 Hz
(b) 20 × 1014 Hz
(c) 10 × 1014 Hz
(d) 5 × 1014 Hz 

Answer: D

Question. Zener diode is used for
(a) amplification
(b) rectification
(c) stabilisation
(d) producing oscillations in an oscillator. 

Answer: C

Question. In a p-n junction photo cell, the value of the photoelectromotive force produced by monochromatic light is proportional to
(a) the barrier voltage at the p-n junction
(b) the intensity of the light falling on the cell
(c) the frequency of the light falling on the cell
(d) the voltage applied at the p-n junction.

Answer: B

Question. The device that can act as a complete electronic circuit is
(a) junction diode
(b) integrated circuit
(c) junction transistor
(d) zener diode.

Answer: B

Question. For transistor action, which of the following statements is correct?
(a) Base, emitter and collector regions should have same doping concentrations.
(b) Base, emitter and collector regions should have same size.
(c) Both emitter junction as well as the collector junction are forward biased.
(d) The base region must be very thin and lightly doped.

Answer: D

Question. In a common emitter transistor amplifier the audio signal voltage across the collector is 3 V. The resistance of collector is 3 kW. If current gain is 100 and the base resistance is 2 kW, the voltage and power gain of the amplifier is
(a) 15 and 200
(b) 150 and 15000
(c) 20 and 2000
(d) 200 and 1000

Answer: B

Question. For CE transistor amplifier, the audio signal voltage across the collector resistance of 2 kW is 4 V. If the current amplification factor of the transistor is 100 and the base resistance is 1 kW, then the input signal voltage is
(a) 10 mV
(b) 20 mV
(c) 30 mV
(d) 15 mV

Answer: B

Question. A npn transistor is connected in common emitter configuration in a given amplifier. A load resistance of 800 W is connected in the collector circuit and the voltage drop across it is 0.8 V. If the current amplification factor is 0.96 and the input resistance of the circuit is 192 W, the voltage gain and the power gain of the amplifier will respectively be
(a) 4, 4
(b) 4, 3.69
(c) 4, 3.84
(d) 3.69, 3.84

Answer: C

Question. In a CE transistor amplifier, the audio signal voltage across the collector resistance of 2 kW is 2 V. If the base resistance is 1 kW and the current amplification of the transistor is 100, the input signal voltage is
(a) 0.1 V
(b) 1.0 V
(c) 1 mV
(d) 10 mV

Answer: D 

Question. If a full wave rectifier circuit is operating from 50 Hz mains, the fundamental frequency in the ripple will be
(a) 25 Hz
(b) 50 Hz
(c) 70.7 Hz
(d) 100 Hz 

Answer: D

Question. A p-n junction diode can be used as
(a) condenser
(b) regulator
(c) amplifier
(d) rectifier

Answer: D

Question. An LED is constructed from a p-n junction diode using GaAsP. The energy gap is 1.9 eV. The wavelength of the light emitted will be equal to
(a) 10.4 × 10^–26 m
(b) 654 nm
(c) 654 Å
(d) 654 × 10^–11 m

Answer: B

Question. The cause of the potential barrier in a p-n junction diode is
(a) depletion of negative charges near the junction
(b) concentration of positive charges near the junction
(c) depletion of positive charges near the junction
(d) concentration of positive and negative charges near the junction. 

Answer: D

Question. A semiconducting device is connected in a series circuit with a battery and a 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 be
(a) a p-type semiconductor
(b) an intrinsic semiconductor
(c) a p-n junction
(d) an n-type semiconductor

Answer: C

Question. Barrier potential of a p-n junction diode does not depend on
(a) diode design
(b) temperature
(c) forward bias
(d) doping density

Answer: A

Important Questions for NCERT Class 12 Physics Semiconductor Devices

Question. The input resistance of a silicon transistor is 100 W.
Base current is changed by 40 mA which results in a change in collector current by 2 mA. This transistor is used as a common emitter amplifier with a load resistance of 4 kW. The voltage gain of the amplifier is
(a) 2000
(b) 3000
(c) 4000
(d) 1000 

Answer: A

Question. A transistor is operated in common emitter configuration at VC = 2 V such that a change in the base current from 100 mA to 300 mA produces a change in the collector current from 10 mA to 20 mA. The current gain is
(a) 50
(b) 75
(c) 100
(d) 25 

Answer: A

Question. A common emitter amplifier has a voltage gain of 50, an input impedance of 100 W and an output impedance of 200 W. The power gain of the amplifier is
(a) 500
(b) 1000
(c) 1250
(d) 50

Answer: C

Question. A transistor is operated in common-emitter configuration at VC = 2 V such that a change in the base current from 100 mA to 200 mA produces a change in the collector current from 5 mA to10 mA.
The current gain is
(a) 100
(b) 150
(c) 50
(d) 75

Answer: C

Question. The voltage gain of an amplifier with 9% negative feedback is 10. The voltage gain without feedback will be
(a) 1.25
(b) 100
(c) 90
(d) 10 

Answer: B

Question. A transistor is operated in common emitter configuration at constant collector voltage VC = 1.5 V such that a change in the base current from 00 mA to 150 mA produces a change in the collector current from 5 mA to 10 mA. The current gain b is
(a) 50
(b) 67
(c) 75
(d) 100

Answer: D

Question. The transfer ratio b of a transistor is 50. The input resistance of the transistor when used in the commonemitter configuration is 1 kW. The peak value of the collector A.C. current for an A.C. input voltage of 0.01 V peak is
(a) 0.25 mA
(b) 0.01 mA
(c) 100 mA
(d) 500 mA 

Answer: D

Question. When npn transistor is used as an amplifier, then
(a) electrons move from collector to base
(b) holes move from base to emitter
(c) electrons move from base to collector
(d) electrons move from emitter to base. 

Answer: C

Question. The part of the transistor which is heavily doped to produce large number of majority carriers is
(a) emitter
(b) base
(c) collector
(d) any of the above depending upon the nature of transistor 

Answer: A

Question. To use a transistor as an amplifier
(a) the emitter base junction is forward biased and the base collector junction is reversed biased
(b) no bias voltage is required
(c) both junction are forward biased
(d) both junction are reverse biased.

Answer: A

Question. Radiowaves of constant amplitude can be generated with
(a) FET
(b) filter
(c) rectifier
(d) oscillator

Answer: D

Question. Which one of the following bonds produces a solid that reflects light in the visible region and whose electrical conductivity decreases with temperature and has high melting point?
(a) metallic bonding
(b) van der Waal’s bonding
(c) ionic bonding
(d) covalent bonding 

Answer: A

Question. Sodium has body centred packing. Distance between two nearest atoms is 3.7 Å. The lattice parameter is
(a) 4.3 Å
(b) 3.0 Å
(c) 8.6 Å
(d) 6.8 Å

Answer: A

Question. If the lattice parameter for a crystalline structure is 3.6 Å, then the atomic radius in fcc crystal is
(a) 2.92 Å
(b) 1.27 Å
(c) 1.81 Å
(d) 2.10 Å

Answer: B

Question. In a p-n junction
(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. 

Answer: A

Question. The device that can act as a complete electronic circuit is
(a) junction diode
(b) integrated circuit
(c) junction transistor
(d) zener diode.

Answer: B

Question. The increase in the width of the depletion region in a p-n junction diode is due to
(a) forward bias only
(b) reverse bias only
(c) both forward bias and reverse bias
(d) increase in forward current

Answer: B 

Question. For transistor action, which of the following statements is correct?
(a) Base, emitter and collector regions should have same doping concentrations.
(b) Base, emitter and collector regions should have same size.
(c) Both emitter junction as well as the collector junction are forward biased.
(d) The base region must be very thin and lightly doped.

Answer: D

Question. Zener diode is used for
(a) amplification
(b) rectification
(c) stabilisation
(d) producing oscillations in an oscillator. 

Answer: C

Question. In a p-n junction photo cell, the value of the photoelectromotive force produced by monochromatic light is proportional to
(a) the barrier voltage at the p-n junction
(b) the intensity of the light falling on the cell
(c) the frequency of the light falling on the cell
(d) the voltage applied at the p-n junction.

Answer: B

Question. In a p-n junction diode, change in temperature due to heating
(a) affects only reverse resistance
(b) affects only forward resistance
(c) does not affect resistance of p-n junction
(d) affects the overall V - I characteristics of p-n junction.

Answer: D

Question. In forward biasing of the p-n junction  
(a) the positive terminal of the battery is connected to p-side and the depletion region becomes thick.
(b) the positive terminal of the battery is connected to n-side and the depletion region becomes thin.
(c) the positive terminal of the battery is connected to n-side and the depletion region becomes thick.
(d) the positive terminal of the battery is connected to p-side and the depletion region becomes thin.

Answer: D

Question. Application of a forward bias to a p-n junction
(a) widens the depletion zone
(b) increases the potential difference across the depletion zone
(c) increases the number of donors on the n side
(d) decreases the electric field in the depletion zone.

Answer: D

Question. Reverse bias applied to a junction diode
(a) lowers the potential barrier
(b) raises the potential barrier
(c) increases the majority carrier current
(d) increases the minority carrier current

Answer: B

Question. In a junction diode, the holes are due to
(a) extra electrons
(b) neutrons
(c) protons
(d) missing of electrons

Answer: D

Question. Which logic gate is represented by the following combination of logic gate ? 

(a) NAND
(b) AND
(c) NOR
(d) OR

Answer: B

Question. If in a p-n junction, a square input signal of 10 V is applied as shown, then the output across R_L will be 

Answer: C

Question. In the given figure, a diode D is connected to an external resistance R = 100 Ω and an e.m.f. of 3.5 V. If the barrier potential developed across the diode is 0.5 V, the current in the circuit will be:
(a) 40 mA
(b) 20 mA
(c) 35 mA
(d) 30 mA

Answer: D

Question. The input signal given to a CE amplifier having a voltage gain of 150 is Vi = 2 cos (15t + π/3) . The corresponding output signal will be : 

Answer: C

Question. Consider the junction diode as ideal. The value of current flowing through AB is :
(a) 0 A
(b) 10^–2 A
(c) 10^–1 A
(d) 10^–3 A

Answer: B

Question. Two ideal diodes are connected to a battery as shown in the circuit. The current supplied by the battery is 

(a) 0.75 A
(b) zero
(c) 0.25 A
(d) 0.5 A

Answer: D

Question. The value of β
(a) is always less than 1
(b) lies between 20 and 200
(c) is always greater than 200
(d) is always infinity

Answer: B

Question. In an unbiased p-n junction, holes diffuse from the p-region to n-region because of 
(a) the potential difference across the p-n junction
(b) the attraction of free electrons of n-region
(c) the higher hole concentration in p-region than that in n-region
(d) the higher concentration of electrons in the n-region than that in the p-region

Answer: C

Question. To get output 1 for the following circuit, the correct choice for the input is
(a) A = 0, B = 1, C = 0
(b) A = 1, B = 0, C = 0
(c) A = 1, B = 1, C = 0
(d) A = 1, B = 0, C = 1

Answer: D

Question. In a common emitter transistor amplifier the audio signal voltage across the collector is 3V. The resistance of collector is 3 kΩ. If current gain is 100 and the base resistance is 2 kΩ, the voltage and power gain of the amplifier is 
(a) 15 and 200
(b) 150 and 15000
(c) 20 and 2000
(d) 200 and 1000

Answer: B

Question. The given electrical network is equivalent to :
(a) OR gate
(b) NOR gate
(c) NOT gate
(d) AND gate

Answer: B

Question. The input resistance of a silicon transistor is 100 W. Base current is changed by 40 mA which results in a change in collector current by 2 mA. This transistor is used as a common emitter amplifier with a load resistance of 4 KW. The voltage gain of the amplifier is
(a) 2000
(b) 3000
(c) 4000
(d) 1000

Answer: A

Question. In a common emitter (CE) amplifier having a voltage gain G, the transistor used has transconductance 0.03 mho and current gain 25. If the above transistor is replaced with another one with transconductance 0.02 mho and current gain 20, the voltage gain will be
(a) 1.5 G
(b) 1/3 G
(c) 5/4 G
(d) 2/3 G

Answer: D

Directions for : Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer from the following-
(a) Statement -1 is true, Statement-2 is true; Statement -2 is a correct explanation for Statement-1
(b) Statement -1 is true, Statement-2 is true; Statement -2 is not a correct explanation for Statement-1
(c) Statement -1 is true, Statement-2 is false
(d) Statement -1 is false, Statement-2 is true

Question. Statement-1 : NOT gate is also called invertor circuit.
Statement-2 : NOT gate inverts the input order.

Answer: A

Question. Statement 1 : If the temperature of a semiconductor is increased then it’s resistance decreases.
Statement 2 : The energy gap between conduction band and valence band is very small.

Answer: A

Question. Statement 1 : A pure semiconductor has negative temperature coefficient of resistance.
Statement 2 : In a semiconductor on raising the temperature, more charge carriers are released, conductance increases and resistance decreases.

Answer: A

Question. Statement-1 : When two semi conductor of p and n type are brought in contact, they form p-n junction which act like a rectifier.
Statement-2 : A rectifier is used to convent alternating current into direct current.

Answer: B

Question. Statement 1 : Diode lasers are used as optical sources in optical communication.
Statement 2 : Diode lasers consume less energy.

Answer: C

Question. Statement 1 : A transistor amplifier in common emitter configuration has a low input impedence.
Statement 2 : The base to emitter region is forward-biased.

Answer: A

Question. Statement-1 : NAND or NOR gates are called digital building blocks.
Statement-2 : The repeated use of NAND (or NOR) gates can produce all the basis or complicated gates.

Answer: A