Semiconductor Devices PYQs Set 2 (PDF)

Set 2 of 17 · Questions 31-60 of 501

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Mere Teacher · Previous Year Questions JEE Main Physics · Semiconductor Devices · Set 2 (Q31-60)
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31. $An n -type and a p -type silicon semiconductor can be obtained by doping pure silicon with$ (1) $indium and sodium respectively$ (2) $boron and arsenic respectively$ (3) $arsenic and boron respectively$ (4) $sodium and magnesium respectively.$ 32. $The hole and the free electron concentrations in a pure silicon at room temperature are given by 1.4 \times 10^{16} m^{- 3} each under equiiibrium. When it is doped with indium and the hole concentration is n_{h} = 4 \times 10^{22} m^{- 3}, the electron concentration is$ (1) $0.49 \times 10^{10} m^{- 3}$ (2) $0.14 \times 10^{10} m^{- 3}$ (3) $0.36 \times 10^{10} m^{- 3}$ (4) $0.72 \times 10^{10} m^{- 3}$ 33. $The positive feedback is required by an amplifier to act an oscillator. The feedback here means:$ (1) $External input is necessary to sustain ac signal in output.$ (2) $A portion of the output power is returned back to the input.$ (3) $Feedback can be achieved by LR network.$ (4) $The base-collector junction must be forward biased.$ 34. $If a small amount of pentavalent atoms is added to germanium crystal :$ (1) $It becomes a p-type semiconductor$ (2) $the antimony becomes an acceptor atom$ (3) $there will be more free electrons than holes in the semiconductor$ (4) $its resistance is increased$ 35. $LED is constructed from Ga - As - P semiconducting material. The energy gap of this LED is 1.9 eV . Calculate the wavelength of light emittedand its colour. (h = 6.63 \times 10^{- 34} Js) and c = 3 \times 10^{8} ms^{- 1}$ (1) $654 nm and red colour$ (2) $1046 nm and blue colour$ (3) $1046 nm and red colour$ (4) $654 nm and orange colour$ 36. $Which of the following gives a reversible operation ?$ (1) (2) (3) (4) 37. $The temperature dependence of resistances of Cu and undoped Si in the temperature range 300 - 400 K, is best described by:$ (1) $Linear increase for Cu, exponential increase for Si$ (2) $Linear increase for Cu, exponential decrease for Si$ (3) $Linear decrease for Cu, linear decrease for Si$ (4) $Linear increase for Cu, linear increase for Si$ 38. $Regarding a semiconductor which one of the following is wrong. [2004]$ (1) $There are no free electrons at room temperature$ (2) $There are no free electrons at 0 K$ (3) $The number of free electrons increases with rise of temperature$ (4) $The charge carriers are electrons and holes$ 39. $In a......biased p-n junction the net flow holes is from n-region to the p-region-$ (1) $forward$ (2) $reverse$ (3) $no$ (4) $both (a) and (b)$ 40. $In an n - p - n transistor, the collector current is 28 mA . If 80 % of electrons reach the collector, its base current in mA is$ (1) $35$ (2) $24$ (3) $14$ (4) $7$ 41. $In a transistor amplifier, the voltage gain is$ (1) $same for all frequencies.$ (2) $high for high frequencies and low for low frequencies.$ (3) $low for high frequencies and high for low frequencies.$ (4) $low for high and low frequencies and constant at mid frequencies$ 42. $Which of the following statement is not true?$ (1) $the resistance of an intrinsic semiconductor decreases with increase in temperature$ (2) $doping pure Si with trivalent impurities gives p -type semiconductor$ (3) $the majority carriers in n -type semiconductors are holes$ (4) $a p - n junction can act as a semiconductor diode$ 43. $Which one of the following statement is false? [2010]$ (1) $Pure Si doped with trivalent impurities gives a p ‐type semiconductor$ (2) $Majority carriers in a n ‐type semiconductor are holes$ (3) $Minority carriers in a p ‐type semiconductor are electrons$ (4) $The resistance of intrinsic semiconductor decreases with increase of temperature$ 44. $A common emitter amplifier has a voltage gain of 50, an input impedance of 100 Ω and an output impedance of 200 Ω. The power gain of the amplifier is$ (1) $500$ (2) $1000$ (3) $1250$ (4) $50$ 45. $For a transistor, β = 100 . The value of α is$ (1) $1.01$ (2) $0.99$ (3) $100$ (4) $0.01$ 46. $For CE transistor amplifier, the audio signal voltage across the collector resistance of 2 kΩ is 4 V. If the current amplification factor of the transistor is 100 and the base resistance is 1 kΩ, then the input signal voltage is [2016]$ (1) $30 mV$ (2) $15 mV$ (3) $10 mV$ (4) $20 mV$ 47. $In the case of forward biasing of a p - n junction diode, which one of the following figures correctly depicts the direction of conventional current (indicated by an arrow mark)?$ (1) (2) (3) (4) 48. $For a common-emitter transistor amplifier, the current gain is 60 . If the emitter current is 6.6 mA, then its base current is$ (1) $6.492 mA$ (2) $0.108 mA$ (3) $4.208 mA$ (4) $0.343 mA$ 49. $Statement I: Photovoltaic devices can convert optical radiation into electricity. Statement II: Zener diode is designed to operate under reverse bias in breakdown region. In the light of the above statements, choose the most appropriate answer from the options given below [NEET 2023]$ (1) $Both Statement I and Statement II are incorrect.$ (2) $Statement I is correct but Statement II is incorrect.$ (3) $Statement I is incorrect but Statement II is correct.$ (4) $Both Statement I and Statement II are correct.$ 50. $In a NAND Gate, A and B are inputs and Y is the output, then the correct option is$ (1) $A = 0, B = 0; Y = 0$ (2) $A = 0, B = 1; Y = 0$ (3) $A = 1, B = 0; Y = 0$ (4) $A = 1, B = 1; Y = 0$ 51. $Conductivity of a photodiode starts changing only if the wavelength of incident light is less than 660 nm . The band gap of photodiode is found to be (\frac{X}{8}) eV . The value of X is ; (Given, h = 6.6 \times 10^{- 34} Js, e = 1.6 \times 10^{- 19} C)$ (1) $15$ (2) $11$ (3) $13$ (4) $21$ 52. $Three amplifiers with voltage gains 10,20 and 30 are connected in series. If the input signal has a peak value of 1 mV then the peak value of the output voltage is$ (1) $6 V$ (2) $60 V$ (3) $0.6 V$ (4) $0.06 V$ 53. $A light emitting diode (LED) has a voltage drop of 2 V across it and passes a current of 10 mA . When it operates with a 6 V battery through a limiting resistor R . The value of R is [2006]$ (1) $400Ω$ (2) $4 K$ (3) $200Ω$ (4) $40 kΩ$ 54. $For a transistor, the current ratio a_{dc} = \frac{69}{70} . The current gain β_{dc} is$ (1) $66$ (2) $67$ (3) $69$ (4) $71$ 55. $The number of beta particles emitted by a radioactive substance is twice the number of alpha particles emitted by it. The resulting daughter is an [2009]$ (1) $isobar of parent$ (2) $isomer of parent$ (3) $isotone of parent$ (4) $isotope of parent$ 56. $The solids which have the negative temperature coefficient of resistance are [NEET 2020]$ (1) $insulators only$ (2) $semiconductors only$ (3) $insulators and semiconductors$ (4) $metals$ 57. $For extrinsic semiconductors: when doping level is increased;$ (1) $Fermi-level of p and n - type semiconductors will not be affected.$ (2) $Fermi-level of p - type semiconductors will go downward and Fermi-level of n - type semiconductor will go upward.$ (3) $Fermi-level of both p-type and n-type semiconductors will go upward for T > T_{F} K and downward for T < T_{F} K, where T_{F} is Fermi temperature.$ (4) $Fermi-level of p - type semiconductor will go upward and Fermi-level of n - type semiconductors will go downward.$ 58. $Consider the following statements (A) and (B) and identify the correct answer. [NEET 2021](A) A zener diode is connected in reverse bias, when used as a voltage regulator.(B) The potential barrier of p - n junction lies between 0.1 V to 0.3 V .$ (1) $(A) and (B) both are correct.$ (2) $(A) and (B) both are incorrect.$ (3) $(A) is correct but (B) is incorrect.$ (4) $(A) is incorrect but (B) is correct.$ 59. $A transistor is used in an amplifier circuit in common emitter mode. If the base current changes by 100 μ A, it brings a change of 10 mA in collector current. If the load resistance is 2 k Ω and input resistance is 1 k Ω, the value of power gain is x x 104. The value of x is______.$ 60. $In a semiconductor, the number density of intrinsic charge carriers at 2 7^{0} C is 1.5 x 1 0^{16} / m^{3} . If the semiconductor is doped with impurity atom, the hole density increases to 4.5 x 1 0^{22} / m^{3} . The electron density in the doped semiconductor is x 1 0^{9} / m^{3} .$