Semiconductors Questions and Answers

In a transistor amplifier when the signal changes by 0 04 V the base current changes by 20 A and collector current by 2 mA If collector load Re 10kn and R 20k Then find the voltage gain A 111

An NPN transistor circuit is arranged as shown in figure It is 1 in Question Type Single Correct Type 2 N P N R A common base amplifier circuit V A common emitter amplifier circuit out 3 A common collector amplifier circuit

Example Design base resistor bias circuit for a CE amplifier such that operating point is VCE 8V and 1 2 mA You are supplied with a fixed 15V d c supply and a silicon transistor with B 100 Take base emitter voltage VE 0 6V Calculate also the value of load resistance that would be employed

Example consider silicon at T 300 K so that N 2 8 10 cm3 and N 1 04 10 cm If we assume the Fermi energy is 0 25 eV below the conduction band calculate the thermal equilibrium concentrations of electrons and holes The bandgap energy of silicon is 1 12 eV

A transistor is used as an amplifier in CB mode with a load resistance of 5KQ The current gain of amplifier is 0 98 and input resistance is 700 the voltage gain and power gain respectively are Question Type Single Correct Type 170 68 6 2 80 75 6 3 60 66 6

stor 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 NEET 2013 a 1 5G 0q Ugal c 5G b 1 3 G 2 G d G

103 The output from a NAND gate is divided into two in parallel and fed to another NAND gate The resulting gate is a NEET Kar 2013 cititos A Be a c NOT gate NOR gate C b AND gate d OR gate C

7 To get an output Y 1 in given circuit which of the following input will be correct 2012M B C A a 1 b 1 c 1 d 0 B 0 0 1 1 C 0 1 0 0 Y

SICS Topic wise 95 The figure shows a logic circuit with two inputs A and B and the output C The voltage wave forms across A B and C are as given The logic 2012 circuit gate is B C 1 1 a OR gate c AND gate The 13 t4 ts 16 b NOR gate d NAND gate a silicon transistor is

12V 1kQ ww 1 switch 2 ILL 50mH 10092 www 5V 3 15 points In the R L circuit shown above the switch has been in position 1 for a very long time Then at t 0 the switch is moved to position 2 a Find the initial inductor current IL at t 0 b Find the circuit time constant when the switch is in position 2 c Find the final inductor current after switch is in position 2 for a very long time

In common base configuration transistor power gain is 800 and voltage gain is 840 If base current is 1 2 mA then collecter current will Question Type Single Correct Type 1 24 mA 2 12 MA 3 6 MA

Three photodiodes D D2 and D3 are made of semiconductors having band gaps of 2 5 eV 2eV and 3 eV respectively Which one will be able to detect light of wavelength 6000 Question Type Single Correct Type 1 D 2 D 3 D D

Three semiconductors are arranged in the increasing order of their energy gap as follows The correct arrangement is Question Type Single Correct Type 1 Tellurium germanium silicon 2 Tellurium silicon germanium 3 Silicon germanium tellurium 4 Silicon tellurium germanium

d cova lent The device that can act as a complete electronic circuit is 2010 a junction diode b integrated circuit c junction transistor d zener diode

electron n and hole n concentrations of 1 5 x 1016 m 3 Doping by indium increases nh to 4 5 x 1022 m 3 The doped semiconductor is of 2011M a n type with electron concentration n 5 x 10 m 3 b p type with electron concentration n 2 5 1010 m 3 c n type with electron concentration 2 5 1023 m 3 d p type having electron concentration De De 5 x 109 m 3

Select the correct statement 1 In unbiased p n junction junction grows when Idiffusion Idrift 2 Drift current flows due to minorities from p to n side 3 In forward bias below the knee point Idiffusion Idrift 4 None of these

In which of the following statements the obtained impure semiconductor is of p type 1 Germanium is doped with bismuth 2 Silicon is doped with antimony 3 Germanium is doped with gallium Silicon is doned with phosphorus

1 2 B NOR gate X AND gate ABC 000 100 Question Type Single Correct Type C D1 11 1 When the output of X is connected to the input Y the resulting combination is equivalent to A B3 0 1 1 0 Y B

Question Type Single Correct Type 1 N type germanium is negatively charged and P type germanium is positively charged 2 Both N type and P type germanium are neutral 3 N type germanium is positively charged and P type germanium is negatively charged Both N type and P type germanium are

The transfer ratio current gain of a transistor is 50 The input resistance of the transistor when used in the common emitter configuration is 1KQ The peak Value for an A C input voltage of 0 01 V peak is Question Type Single Correct Type 1 100 A 2 0 01 MA 3 0 25 mA

logic gate wiet switch watum burol wine a Padov It flow Diber it will offer R ndulum e Mexistence dulum il are ively d oil 1 NOR 3 OR 4 00 i B 0 i www R C LED Y 2 AND 4 NAND

To get an output below the input must be A a 0 b 0 c 1 B C 11 01 0 0 1 0 shown 2010 Y 84 85

The drift velocity of free electrons in a conductor of length 6 m is 0 25 ms under the application of potential difference of 100 V The mobility of free electrons is 2 x 103 m V S 1 2 5 x 10 2 m V s 1 1 5 x 10 m V S 1 1 5 x 10 m V S 1

73 A p n photodiode is fabricated from a semiconductor with a band gap of 2 5 eV It can detect a signal of wavelength 2009 a 4000 nm c 4000 b 6000 nm d 6000 81 A B

55 In the following circuit the output Y for all possible inputs A and B is expressed by the truth table 2007 A B a ABY 011 011 101 110 c ABY 000 011 101 A B b ABY 001 010 100 110 d ABY 000 010 100 111 Y 70 a c 1 A p r band the ra is ne a c 71 The is e a c 72 The are

d 6000 A configuration A transistor is operated in common emitter at V 2 V such that a change in the base current from 100 A to 200 A produces a change in the collector current from 5 mA to 10 mA The current gain is 2009 a 100 c 50 b 150 2 75

Two cells of emfs approximately 5V and 10V are to be accurately compared using a potentiometer of length 400 cm NCERT Exemplar a The battery that runs the potentiometer should have voltage of 8V b The battery of potentiometer can have a voltage of 15 V and R adjusted so that the potential drop across the wire slightly exceeds 10 V c The first portion of 50 cm of wire itself should have potential drop of 10 V d Potentiometer is usually used for comparing resistan and not voltages

A compound generator is to supply a load of 250 lamps each rated at 100W 250 V the armature series and shunt windings have resistances of 0 06 2 0 04 2 and 50 respectively Determine the generated e m f when the machine is connected in i long shunt ii short shunt Take brush drop as 1 V per brush 6

A long cylinder having a diameter of 2 cm is maintained at 600 C and has an emissivity of 0 4 Surrounding the cylinder is another long thin walled concentric cylinder having a diameter of 6 cm and an emissivity of 0 2 on both the inside and outside surfaces The assembly is located in a large room having a temperature of 27 C Calculate the net radiant energy lost by the 2 cm diameter cylinder per meter of length Also calculate the temperature of the 6 cm diameter cylinder

A transistor configuration is operated in common emitter at V 2 V such that a change in the base current from 100 A to 300 A produces a change in the collector current from 10 mA to 20 mA The current gain is 1 25 3 75 AIPMT Prelims 2011 2 50 4 100

9 Pure Si at 500 K has equal number of electron n and hole n concentrations of 1 5 x 1016 m Doping by indium increases n to 4 5 102 m 3 The doped semiconductor is of AIPMT Mains 2011 1 n type with electron concentration n 2 5 1023 m 3 2 p type having electron concentrations n 5 x 10 m e 3 n type with electron concentration n 2 5 1022 m 3 e 4 p type with electron concentration n 2 5 1010 m 3 e

The input resistance of a silicon transistor is 100 0 Base current is changed by 40 A 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 k The voltage gain of the amplifier is AIPMT Mains 2012 1 2000 2 3000 3 4000 4 1000

wo identical balls are interconnected with a light and inextensible thread having length I The system is on a smooth horizontal table with the thread just taut Initial velocities of both as shown The kinetic nergy of the system after the string gets tout

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 NEET 2019 Odisha 1 654 x 10 11 m 3 654 nm 2 10 4 10 26 m 4 654 A

16 Current in the circuit will be 200 www tak 43 3 2 8 D ww 200 40 a A b c 20 AAAA KH 300 www SV 17 The diode used in the circuit shown in the figure has

A Zener diode having breakdown voltage equal to 15 V is used in a voltage regulator circuit shown in the figure The current through the diode is 1 10 mA 3 20 mA 20 V 2500 ww 15 V 2 15 mA 4 5 mA 1 k

An n p n transistor circuit is arranged as shown the figure It is a common Vin N P N www1 1 1 Base amplifier circuit 2 Emitter amplifier circuit 3 Collector amplifier circuit 4 None of these R out Medica Divis

M 1 0 4m M 4m 2 M 0 M M 4m 0 M M 4m 3 If the ratio of the concentration of electrons and that of holes in a semiconductor is 7 5 and the ration their currents is 7 4 then the ratio of their drift velocities is 1 4 7 2 5 8 3 4 5 0 4 5 4

Example 1 Fig 3 4 shows biasing with base resistor method Determine i the collector current Ic and collector emitter voltage VCE neglecting base emitter voltage ii If RB is changed to 50 K find the new operating point Given that 50

the emitter n the base t ification fact nmon ba base curre would b ing to A A B AB AB emitte ro for pre below is The expression of Y in following circuit is A alue of D M B C ABCD A B C D The combination of gates shown below yields A B a NAND gate C NOT gate the gates shown in the b A B A B d A B AB BO b A BCD d AB CD b OR gate d XOR gate In the circuit below A and B represent two inputs and C represents the output the circuit represents AO OC b AND gate d OR gate 40 The Boolean expression for the gate circuit shown below is a NOR gate e NAND gate I a 4 A 1 C A A A B 41 Identify the gate represented by the block diagram as shown in fig a AND gate c NAND gate 42 The logic gate having an output of 1 is a iv c ii b 4 1 1 A B 200 b NOT gate d NOR gate 43 The input of A and B for the Boolean expression H b 1 d iii 1 is b01

35 In a given circuit as shown the two input wave forms A and B are applied simultaneously D C d B a b A The resultant wave form at Y is 7 Y

33 The constant a of a transistor is 0 9 What would be the change in the collector current corresponding to a change of 4 mA in the base current in a common emitter arrangement a 30 mA c 36 mA C 11 b 63 mA d 3 6 mA

9 In a common base mode of transistor collector current is 5 488 mA for an emitter current of 5 60mA The value of the base current amplification factor will be a 48 b 49 c 50 d 51

8 Design the simplest circuit that has three inputs x x2 and x3 which produces an output value of 1 whenever two of the input variables have the value 1 otherwise the output has to be 0 CO2 3MI

220 as figure the diodes are silicon diodes and Vr 0 7V the diodes D1 and D2 should be A B C D 6V D D K D1 on D2 on D1 off D2 off D1 off D2 on D1 on D2 off 3kQ A 12V 25

small balls are interconnected with a light and inextensible thread having length L The system is on a smooth horizontal table with the thread just taut Each ball is imparted a velocity v one towards the other ball and the other in a direction that is perpendicular to the velocity given to the first ball V L V a After how much time the thread will become taut again Calculate the kinetic energy of the system after the string gets taut

59 For the logic circuit shown the truth table is A BO ABY 000 a 0 1 0 100 1 1 1 ABY 001 c 0 1 1 101 10 1 b d ABY 000 0 1 1 101 111 ABY 001 0 1 0 100 1 1 0 Y NEFTC

Q4 A flux quantum fluxoid is approximately equal to 2 x 107 gauss cm A type II superconductor is placed in a small magnetic field which is then slowly increased till the field starts penetrating the superconductor The strength of the field at this point is 2 x 10 gauss The applied field is further increased till superconductivity is completely destroyed The strength of the field is now 8 7 x 10 gauss Find the correlation length of the superconductor

3 A pure Si crystal has 5 1022 atoms m It is doped by 1 ppm concentration of pentavalent impurity The number of holes is n nn Take n 1 5 x 10 6 m a 4 5 x 10 m c 2 5 x 109 m b 4 5 x 106 m 3 d 2 5 x 106 m 3 d hel

20 Increase in temperature of a gas filled in a container would lead to a Increase in its mass b Increase in its kinetic energy c Decrease in its pressure d Decrease in intermolecular distance