Semiconductor Devices PYQs Set 6 (PDF)

Set 6 of 16 · Questions 151-180 of 467

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Mere Teacher · Previous Year Questions NEET Physics · Semiconductor Devices · Set 6 (Q151-180)
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151. $An LED is constructed from a p-n junction diode using GaAsP. The energy gap is 1.9 eV . The wavelength of the light emitted will be equal to$ (1) $10.4 \times 10^{- 26} m$ (2) $654 nm$ (3) $654Å$ (4) $654 \times 10^{- 11} m$ 152. $A Ge specimen is doped with Al. The concentration of acceptor atoms is ‐ 10^{21} atoms / m^{3} . Given that the intrinsic concentration of electron‐hole pairs is \sim 1 0^{19} / m^{3}, the concentration of electrons in the specimen is [2004]$ (1) $1 0^{15} / m^{3}$ (2) $1 0^{17} / m^{3}$ (3) $1 0^{4} / m^{3}$ (4) $1 0^{2} / m^{3}$ 153. $In insulators (C.B. is conduction band and V.B. is valence band)$ (1) $V.B. is partially filled with electrons.$ (2) $C.B. is partially filled with electrons.$ (3) $C.B. is empty and V.B. is filled with electrons.$ (4) $C.B. is filled with electrons and V.B. is empty.$ 154. $For a constant collector-emitter voltage of 8V, the collector current of a transistor reached to the value of 6 mA from 4 mA, whereas base current changed from 20 μ A to 25 μ A value. If transistor is in active state, small signal current gain (current amplification factor) will be:$ (1) $240$ (2) $400$ (3) $0.0025$ (4) $200$ 155. $In a n ‐type semiconductor, which of the following statement is true? [2013]$ (1) $Electrons are majority carriers and trivalent atoms are dopants$ (2) $Electrons are minority carriers and pentavalent atoms are dopants$ (3) $Holes are minority carriers and pentavalent atoms are dopants$ (4) $Holes are majority carriers and trivalent atoms are dopants$ 156. $A p‐n photodiode is made of a material with a band gap of 2.0 eV . The minimum frequency of the radiation that can be absorbed by the material is nearly [2008]$ (1) $10 \times 1 0^{14} Hz$ (2) $5 \times 1 0^{14} Hz$ (3) $1 \times 1 0^{14} Hz$ (4) $20 \times 1 0^{14} Hz$ 157. $In a p‐n junction photo cell, the value of the photo‐ electromotive force produced by monochromatic light is proportional to [2004]$ (1) $the barrier voltage at the p \sim n junction$ (2) $the intensity of the light falling on the cell$ (3) $the frequency of the light falling on the cell$ (4) $the voltage applied at the p‐n junction$ 158. $The following truth table corresponds to the logic gate [2010] A B X 000011101111$ (1) $NAND$ (2) $OR$ (3) $AND$ (4) $XOR$ 159. $Which of the following statements is true about LEDs?$ (1) $High operational voltage$ (2) $Warm-up time is required$ (3) $Bandwidth of light is 4000Å - 7000Å$ (4) $Fast on-off switching$ 160. $For a transistor amplifier, the voltage gain$ (1) $is low at high and low frequencies and constant at mid frequencies$ (2) $remains constant for all frequencies$ (3) $constant at high frequencies and low at low frequencies$ (4) $is high at high and low frequencies and constant in the middle frequency range.$ 161. $A transistor is operated m common emitter configuration at V_{C} = 2 V such that a change in the base current from 100 μA to 300 μA produces a change in the collector current from 10 m A to 20 mA . The current gain is [2011]$ (1) $75$ (2) $100$ (3) $25$ (4) $50$ 162. $In a common-base of mode of transistor, the collector current is 5.488 mA for an emitter current of 5.60 mA. The value of the base current amplification factor (β) will be :$ (1) $49$ (2) $50$ (3) $51$ (4) $48$ 163. $In common emitter transistor amplifier, the output voltage and input voltage have a phase difference of$ (1) $0$ (2) $\frac{π}{2}$ (3) $\frac{5 π}{6}$ (4) $π$ 164. $Consider an n‐p‐n transistor amplifier in common‐emitter configuration. The current gain of the transistor is 100. If the collector current changes by 1 mA, what will be the change in emitter current? I2005]$ (1) $1.01 mA$ (2) $1.1 mA$ (3) $0.01 mA$ (4) $10 mA$ 165. $In a reverse biased diode, when the applied voltage changes by 1 V, the current is found to change by 0.5 μA . The reverse bias resistance of the diode is$ (1) $2 \times 10^{5} Ω$ (2) $2 \times 10^{6} Ω$ (3) $200Ω$ (4) $2Ω$ 166. $Which gate is represented by the following truth table? A B C 001101011110$ (1) $XOR$ (2) $NOT$ (3) $NAND$ (4) $AND$ 167. $Carbon, silicon and germanium have four valence electrons each. At room temperature which one of the following statements is most appropriate?$ (1) $the number of free conduction electrons is significant in C but small in Si and Ge.$ (2) $the number of free conduction electrons is negligibly small in all the three.$ (3) $the number of free electrons for conduction is significant in all the three.$ (4) $the number of free electrons for conduction is significant only in Si and Ge but small in C.$ 168. $In the study of transistor as an amplifier, the ratio of collector current to emitter current is 0.98 , then the ratio of collector current to base current will be$ (1) $99$ (2) $49$ (3) $50$ (4) $98$ 169. $In a p - n junction diode, change in temperature due to heating [NEET 2018]$ (1) $does not affect resistance of p - n junction$ (2) $affects only forward resistance$ (3) $affects only reverse resistance$ (4) $affects the overall V - I characteristics of p-n junction$ 170. $In half-wave rectification, if the input frequency is 60 Hz, then the output frequency would be [NEET 2022]$ (1) $30 Hz$ (2) $60 Hz$ (3) $120 Hz$ (4) $zero$ 171. $A truth table is given below. Which of the following has this type of truth table? [2011] A B Y 110100010001$ (1) $XOR gate$ (2) $NOR gate$ (3) $AND gate$ (4) $OR gate$ 172. $The increase in the width of the depletion region in a p - n junction diode is due to [NEET 2020]$ (1) $reverse bias only$ (2) $both forward bias and reverse bias$ (3) $increase in forward current$ (4) $forward bias only$ 173. $The length of germanium rod is 0.928 cm and its area of cross-section is 1 mm^{2} . If for germanium. n_{1} = 2.5 \times 10^{19} m^{- 3}, μ_{n} = 0.15 m^{2} V^{1} s^{- 1}, μ_{e} = 0.35 m^{2} V^{- 1} s^{- 1} then resistivity is$ (1) $50Ω - cm$ (2) $25Ω - cm$ (3) $50Ω - mm$ (4) $100Ω -m$ 174. $In a transistor, the collector current varies by 0.49 mA and emitter current varies by 0.50 mA . Current gain β measured is$ (1) $49$ (2) $150$ (3) $99$ (4) $100$ 175. $Which one of the following statement is false?$ (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) $The resistance of intrinsic semiconductor decreases with increase of temperature.$ 176. $When a semiconductor is doped with donor impurity$ (1) $the hole concentration decreases and electron concentration increases$ (2) $the hole concentration increases and electron concentration decreases.$ (3) $both hole concentration and electron concentration increase$ (4) $both hole concentration and electron concentration decrease$ 177. $Carbon, silicon and germanium have four valence electrons each. These are characterized by valence and conduction bands separated by energy band gap respectively equal to (Eg)_{C}, (Eg)_{Si} and (Eg)_{Ce} . Which of the following statements is true? [2005]$ (1) $(Eg)_{Si} < (Eg)_{Ge} < (Eg)_{C}$ (2) $(Eg)_{C} < (Eg)_{Ge} > (Eg)_{Si}$ (3) $(Eg)_{C} > (Eg)_{Si} > (Eg)_{Ge}$ (4) $(Eg)_{c} = (Eg)_{Si} = (Eg)_{Ge}$ 178. $For a transistor α and β are given as α = \frac{I _{C}}{I _{E}} and β = \frac{I _{C}}{I _{B}} . Then the correct relation between α and β will be:$ (1) $α = \frac{1 - β}{β}$ (2) $β = \frac{α}{1 - α}$ (3) $αβ = 1$ (4) $α = \frac{β}{1 - β}$ 179. $The radius of germanium (Ge) nuclide is measured to be twice the radius of 49 Be . The number of nucleons in Ge are [2006]$ (1) $73$ (2) $74$ (3) $75$ (4) $72$ 180. $In a transistor, a change of 8.0 mA in the emitter current produces a change of 7.8 mA in the collector current. What change in the base current is necessary to produce the same change in the collector current [2011]$ (1) $50 μA$ (2) $100 μA$ (3) $150 μA$ (4) $200 μA$