Contents
NEET Physics Chapter Wise Mock Test – Electronic Devices
Question 1.
The correct relation for the cohesive energy is
(a) Cohesive energy = free energy of atoms – crystal energy
(b) Cohesive energy = free energy of atoms + crystal energy
(c) Cohesive energy = free energy of atoms/crystal energy
(d) Cohesive energy = free energy of atoms x crystal energy
Question 2.
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 n-region
(d) All of the above
Question 3.
A specimen of silicon is to be made p-type semiconductor. For this one atom of indium, on an average, is doped in 5×107 silicon atoms. If the number density of silicon is 5 x1028 atoms/m2, then the number of acceptor atoms per cm3 will be
(a) 2.5x 1030
(b) 1.0x 1013
(c) 1.0x 1015
(d) 2.5x 1036
Question 4.
In the ratio of the concentration of electrons and 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) 4/7
(b) 5/8
(b) 4/5
(d) 5/4
Question 5.
The conductivity of a semiconductor increases with increase in temperature because
(a) number density of free current carriers increase
(b) relaxation time increases
(c) both number density of carriers and relaxation time increase
(d) number density of current carriers increase, relaxation time decreases but effect of decrease in relaxation time is much less than increase in number density
Question 6.
The ratio of electron and hole currents in a semiconductor is 5/4 and the ratio of drift velocities of electrons and holes is 7/4, then the ratio of concentrations of electrons and holes will be
(a) 25/49
(b) 49/25
(c) 7/5
(d) 5/7
Question 7.
The resistivity of an n-type extrinsic semiconductor is 0.25 Ω-m. If the electron mobility is 8.25 m2/V-s, then the concentration of donor atoms will be (in m-3)
(a) 3.0x 1016
(b) 3.0x 1017
(c) 3.0×1018
(d) 3.0×1019
Question 8.
Question 9.
The contribution in the total current flowing through a semiconductor due to electrons and holes are 3/4 and 1/4. If the drift velocity of the electron is 5/2 times that of holes at this temperature, then the ratio of concentration of electrons and holes is
(a) 6:5
(b) 5:6
(c) 3:2
(d) 2:3
Question 10.
The number of densities of electrons and holes in pure silicon at 27°C are equal and its value is 1.5×1016 m-3. On doping with indium, the hole density increases to 4.5 x 1027 m-3. The electron density in doped silicon will be
(a) 50×109 m-3
(b) 5×109 m-3
(c) 108 m-3
(d) 107 m-3
Question 11.
In n-type germanium, the mobility of electrons is 3900 cm2/Vs and their conductivity is 5 mho/cm. If the cotter contribution is negligible, then impurity concentration will be
(a) 8×1015 per cm3
(b) 9.25×1014 per cm3
(c) 6×1013 per cm3
(d) 9×1013 per cm3
Question 12.
The electron mobility in n-type germanium is 3900 m2/ Vs and its conductivity is 6.24 mho cm-1, then impurity concentration will be, if the effect of cotters is negligible
(a) 1015 cm-3
(b) 1013 cm-3
(c) 1012 cm-3
(d) 1016 cm-3
Question 13.
A potential difference of 2.5 V is applied across the faces of a germanium crystal plate. The face area of the crystal is 1cm2 and its thickness is 1.0 mm. The free electron concentration in germanium is 2×1019 m-3, and the electron and hole mobilities are 0.33 m2/Vs and 0.17 m2/Vs, respectively. The current across the plate will be
(a) 0.2 A
(b) 0.4 A
(c) 0.6 A
(d) 0.8 A
Question 14.
In a common emitter amplifier, the output resistance is 5000Ω and the input resistance is 2000Ω. If the peak value of the signal voltage is 10mV and β=50, then the peak value of the output voltage is
(a) 1.25 V
(b) 125 V
(c) 5 x 10-6 V
(d) 2.5×10-4 V
Question 15.
The input and output resistances in a common base amplifier circuit are 400Ω and 400 kΩ. If the current gain α is 0.98 and emitter current is 2 mA, then the base current is
(a) 0.02 mA
(b) 0.08 mA
(c) 0.05 mA
(d) 0.04 mA
Question 16.
In the given circuit, all diodes are ideal. The current through battery is
(a) 2 A
(b) 1 A
(c) 3 A
(d) 4 A
Question 17.
Current through the ideal diode as shown in figure, is
(a) zero
(b) 20 A
(c) (1/20) A
(d) (1/50)A
Question 18.
A common emitter amplifier has a voltage gain of 50, an input impedance of 100Ω and an output impedance of 200Ω. The power gain of the amplifier is
(a) 500
(b) 1000
(c) 1250
(d) 100
Question 19.
LED has a voltage drop of 2V across it, and passes a current of 10mA. When it operates with a 6 V battery through a limiting resistor R. The value of R is
(a) 40 kΩ
(b) 4 kΩ
(C) 200Ω
(d) 400Ω
Question 20.
The minimum potential difference between the base and emitter required to switch a silicon transistor ON, is approximately
(a) 1V
(b) 3V
(c) 5V
(d) 4.2V
Question 21.
A transistor has α= 0.95. If the emitter is 10mA, then collector current will be
(a) 9.5 mA
(b) 10 mA
(c) 0.95 mA
(d) None of these
Question 22.
In a transistor amplifier, β= 62, RL = 5000Ω and internal resistance of the transistor is 500Ω. The voltage amplification of the amplifier will be
(a) 500
(b) 620
(c) 780
(d) 950
Question 23.
A transistor having α=0.99, is used in a common base amplifier. If the load resistance is 4.5 kΩ and the dynamic resistance of the emitter junction is 50Ω,the voltage gain of the amplifier will be
(a) 79.1
(b) 89.1
(c) 99.1
(d) None of these
Question 24.
The voltage gain of the following amplifier is
(a) 10
(b) 100
(c) 1000
(d) 9.9
Question 25.
A p-n-p transistor is used in common emitter mode in an amplifier circuit. A charge of 40 μA in the base current brings a charge of 2 mA in collector current and of 0.04 V in base emitter voltage. The base current amplification factor is
(a) 5
(b) 50
(c) 500
(d) 0.5
Question 26.
The base resistance RB in the circuit, is (given hFE = 90)
(a) 10 kΩ
(b) 82 kΩ
(c) 100 kΩ
(d) 0.82 kΩ
Question 27.
In a common base transistor circuit IC = 9.7 μA, IB= 0.03 μA, then current gain, α=
(a) 0.97
(b) 0.097
(c) 95
(d) 500
Question 28.
The input resistance of a CE amplifier is 333Ω and the load resistance is 5 kΩ. A change of base current by 15 μA a result in the change of collector current by 1 mA. The voltage gain of the amplifier is
(a) 550
(b) 51
(c) 101
(d) 1001
Question 29.
The combination of the gates shown in the figure below produces
(a) NOR gate
(b) OR gate
(c) AND gate
(d) XOR gate
Question 30.
Question 31.
The following figure shows a logic gate circuit with two inputs A and B, and the output C. The voltage waveform of A, B and C are as shown below
The logic circuit gate is
(a) AND gate
(b) NAND gate
(c) NOR gate
(d) OR gate
Question 32.
How many gates are required to design P=X+X‾Y?
(a) 1
(b) 2
(c) 3
(d) 4
Question 33.
Question 34.
Direction (Q. NOs.35-39): In each of the following questions a statement of Assertion is given followed by a corresponding statement of Reason just below it. Of the statements mark the correct answer as
(a) If both Assertion and Reason are true and the Reason is the correct explanation of the Assertion
(b) If both Assertion and Reason are true but the Reason is not the correct explanation of the Assertion
(c) If Assertion is true but Reason is false
(d) If both Assertion and Reason are false
Question 35.
Assertion (A): In a common base circuit, current gain is 0.95. If base current is 60 μA, then emitter current is 1200 μA.
Reason (R): Current gain in common base circuit is
α=IC/IE
Question 36.
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.
Question 37.
Assertion (A): The temperature coefficient of resistance is positive for metals and negative for p-type semiconductor.
Reason (R): The effective charge carriers in metals are negatively charged, whereas in p -type semiconductor they are positively charged.
Question 38.
Assertion (A): Light Emitting Diode (LED) emits spontaneous radiation.
Reason (R): LED are forward biased p-n junctions.
Question 39.
Assertion (A): When base region has larger width, the collector current increases.
Reason (R): Electron hole combination in base result in-increase of base current.
Question 40.
Depletion layer contains
(a) Only immobile negative and positive ions
(b) Only free charge carrier
(c) Both free carrier and immobile ions
(d) None of the above
Question 41.
Question 42.
Which logic gate is represented by the following combination of logic gates?
(a) OR
(b) NAND
(c) AND
(d) NOR
Question 43.
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 for a solar cell and points 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
Question 44.
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
(b) Only II
(c) II and III
(d) I, II and III
Question 45.
In a n-type semiconductor, which of the following statement is true?
(a) Electrons are majority carriers and trivalent atoms are dopants
(b) Electrons are minority carriers and pentavalent atoms are dopants
(c) Holes are minority carriers and pentavalent atoms are dopants
(d) Holes are majority carriers and trivalent atoms are dopants
Question 46.
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
(a) 2G/3
(b) 1.5 G
(C) G/3
(d) 5G/4
Question 47.
Question 48.
When two semiconductors of p and n-type are brought into contact, they form a p-n junction which acts like a/an
(a) conductor
(b) oscillator
(c) amplifier
(d) rectifier
Question 49.
In the case of constants,α and β of a transisitor
(a) αβ=1
(b) β>1, α<1
(c) α=β
(d) β<1, α>1
Question 50.
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 the semiconductor is
(a) 0.9
(b) 0.7
(c) 0.5
(d) 1.1
Question 51.
Assertion (A): NAND or NOR gates are called digital building blocks.
Reason (R): The repeated use of NAND or NOR gates can produce all the basic or complex gates.
(a) If both Assertion and Reason are true and reason is the correct explanation of Assertion
(b) If both Assertion and Reason are true but the. Reason is not the correct explanation of Assertion
(c) If Assertion is true but Reason is false
(d) If both Assertion and Reason are false
Question 52.
In a transistor, the base is
(a) an insulator
(b) a conductor of low resistance
(c) a conductor of high resistance
(d) an extrinsic semiconductor
Question 53.
Digital circuit can be made by repetitive use of this gate
(a) AND
(b) OR
(c) NOT
(d) NAND
Question 54.
In a CE transistor amplifier, the audio signal voltage across the collector resistance of 2 kΩ is 2 V. If the base resistance is 1kΩ and the current amplification of the transistor is 100, the input signal voltage is
(a) 0.1V
(b) 1.0 V
(c) 1 mV
(d) 10 mV
Question 55.
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
Question 56.
The figure shows a logic circuit with two inputs A and B, and the output C. The voltage waveforms across A, B and C are as given. The logic circuit gate is
(a) OR gate
(b) NOR gate
(c) AND gate
(d) NAND gate
Question 57.
Which one of the following statement is false?
(a) Pure Si doped with trivalent impurities gives a p-type semiconductor
(b) Majority carriers in a n-type semiconductor are holes
(c) Minority carriers in a p-type semiconductor are electrons
(d) The resistance of intrinsic semiconductor decreases with increase of temperature
Question 58.
A proper combination of 3 NOT and 1 AND gates is-shown. If A=0, B=1 and C=1, then the output of this combination is
(a) 1
(b) zero
(c) not predictable
(d) None of these
Question 59.
If a small amount of antimony is added to germanium crystal
(a) the antimony becomes an acceptor atom
(b) there will be more free electrons than holes in the semiconductor
(c) its resistance is increased
(d) it becomes a p-type semiconductor
Question 60.
A common emitter amplifier has a voltage gain of 50, an input impedance of 100Ω and an output impedance of 200Ω. The power gain of the amplifier is
(a) 500
(b) 1000
(c) 1250
(d) 50
Answers:
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