Semiconductors Questions and Answers

has a drop of 0 5 V which is assumed to be independent of current The current in excess of 10 mA through the diode produces large joule heating which damages the diode If we want to use a 1 5 V battery to forward bias the diode the resistor used in series with the diode so that the maximum current does not exceed 5 mA is P 0 5V N SVDH ER

In a NPN transist emitter in 1 us Only 1 of electrons are collector current 1 584 mA O 1 54 mA O 1 273 MA O 1 973 mA

The input resistance of silicon transistor is 600 Q Its base current is changed by 16 A which results in change in collector current by 2 mA This transistor is used as a common emitter amplifier with a load resistance of 3 kQ The voltage gain of transistor is 400 O 625 O 700 O 910

d its resist In the following figure the diodes which are forward biased are 2011M A 5V B 10V C 12V D R www 4 R R www R T SV R 10V 259

The input resistance of silicon transistor is 600 Its base current is changed by 16 A which results in change in collector current by 2 mA This transistor is used as a common emitter amplifier with a load resistance of 3 k The voltage gain of transistor is O 400 O 625 O 700

When electric field is applied across a semi conductor Electrons move from lower energy level to higher energy level in conduction band Holes in valance band move from lower energy level to higher energy level Holes in conduction band move from higher energy level to lower energy level Electrons move from higher energy level to lower energy level in valence band

To use transistor as an amplifier Both junctions are forward biased Both junctions are reversed biased The emitter base junction is forward biased and collector base junction is reverse biased No biasing voltages are required

Which of the following relations is are correct Symbols have their usua meaning NCERT Pg 499 1 B tions Rout Rin a 1 2 Ap B Rout R 4 All of these

The conductivity of semi conductor increases with increase in temperature because Number density of free charge carriers decreases Relaxation time increases Both number density of carriers and relaxation time increases Number density of carrier increases and relaxation time decreases but effect of decrease in relaxation time is much smaller than increase in number density

Q 1 In an n type silicon which of the following statement is true a Electrons are majority carriers and trivalent atoms are the dopants b Electrons are minority carriers and entavalent atoms are the dopants c Holes are minority carriers and entavalent atoms are the dopants d Holes are majority carriers and

Three amplifiers are connected in series cascaded If the voltage gain of amplifiers are 2 dB 4 dB and 10 dB then overall voltage gain of the amplifier will be 1 80 dB 2 16 dB 3 6 dB 4 14 dB

2 To produce high output 1 at R we x and y respectively as X y 1 x 0 y 1 2 x 1 y 1 31 x 1 y 0 I n ty Do R n 1 fety

9 A change of 8 0 mA in the emitter current brings a change of 7 9 mA in the collector current How much change in the base current is required to have the same change 7 9 mA in the collector current Find the values of a and B

Doping of a semiconductor with small traces of impurity atoms generally changes the resistivity as follows 1 does not alter 2 increases 3 decreases 4 may increase or decrease depending on the dopant

A potential barrier of 0 50 V exists across a P N junction If the depletion region is 5 0 x 107 wide the intensity of the electric field in this region is O 1 0 x 10 V m 1 0 x 105 V m 2 0 x 105 V m 2 0 x 106 V m

22 If the lattice constant of this semiconductor is decreased then which of the following is correct AIEEE 2006 Conduction band width Band gap 11 TE E Valence band width I a E and E increase but Eg decrease POT E and E decrease but E increase c All E Eg E decrease 1 Ev

3 cannot be zero 4 none of these 142 A potential barrier of 0 50 V exists across a P N junction If the depletion region is 5 0 x 10 7 m wide th intensity of the electric field in this region is 1 1 0 x 105 V m 2 1 0 x 10 V m 3 2 0 x 10 V m

In the following common emitter circuit if B 100 VCE 7V VBE 0 RC 2K02 then Ig will be R Re 1 3 4 Correct Answer 3 0 01 mA 0 02 mA 0 04 mA 0 06 mA B ww E t l 15V

What will be conductivity of pure silicon crystal at 300 K temperature If electron hole pairs per cm 1 072 x 10 0 at this temperature 1350 cm volt s 480 cm volt s

33 In an unbiased p n junction which of the following is correct 1 p side is at higher potential than n side 2 n side is at higher potential than p side 3 Both p side and n side are at the same potential 4 Any of the above is possible depending upon the carrier density in the two sides

If the lattice constant of this semiconductor is decreased then which of the following is correct 12000 conduction band width band gap valence band width a All E E E increase b E and E increase but E decreases c E and E decrease but E increases d All E E E decrease g Eg E E

A B C and D are input bits and Y is the output bit in the XOR gate circuit of the figure below Which of the following statements about the sum S of A B C D and Y is correct A B C D 1 XOR XOR XOR S is always either zero or odd 2 S is always either zero or even Y

PASSAGE The Hall coefficient of a semiconductor is 3 22 X 10 power 4 m3 C Its resistivity is 9 X 10 power 3 ohm m Read the following passage to answer correct options Marks 2 Current density is given as OPTIONS 4 31 X 10 power 8 A m2 6 31 X 10 power 6 A m2 6 31 X 10 power 7 A m2

23 A transistor is operated in CE configuration at Vcc 2V such that a change in base current from 100 A to 200 A produces a change in the collector current from 9 mA to 16 5 mA The value of current gain is 1 45 2 50 3 60 4 75

20 A junction diode in which one of the p or n sections is made very thin can be used to convert light energy into electrical energy then the diode is called 1 Light emitting diode 2 Zener diode 3 Solar cell 4 Photo diode

The Hall coefficient of a semiconductor is 3 22 X 10 power 4 m3 C Its resistivity is 9 X 10 power 3 ohm m correct options Marks 2 If drift velocity 300 m s Electric field is calculated as OPTIONS

5 Germanium is doped one part per million with indium at room temperature Calculate the conductivity of doped germanium Given concentration of Ge atoms 4 4 x 1028 m 3 intrinsic n 2 4 x 10 9m 3 carrier concentration 0 39 m V s and 0 19 m V s S e 1 1 S Ans 1 34 x 10 ohm m 1

Assume F x y z 1 3 4 5 then the correct OR NAND implementation from the figures below is N X Y X Z X Y X Fig 2 Fig 3 Fig 4 Fig 1 Fig 1 Fig 3 F ZX Y X Z X Y Fig 2 D Fig 4

17 When a diode is forward biased it has a voltage drop of 0 5 V The safe limit of current through the diode is 10 mA If a battery of emf 1 5 V is used in the circuit the value of minimum resistance to be connected in series with the diode so that the current does not exceed the safe limit is 1 300 2 2 502 3 100 2 4 2009

2 5 Take the breakdown voltage of the zener diode used in the given circuit as 6V For the input voltage shown in figure below the time variation of the output voltage is Graphs drawn are schematic and not to scale 10V V 0 if A 1 10V 3 R www A t hr A 2 A

Q 3 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 O 10 10Hz O 5 10 44 Hz 4 1 00 14 1 10 4 Hz

The reverse bias in a junction diode is changed from 5V to 15V then the value of current changes from 38 A to 88 A The resistance of junction diode will be 1 4 x 105 2 3 105 2 3 2 x 105 4 106 2

1 0 V 2 5 V 3 10 V 4 Any of these 168 Five diodes and three resistors are connected along with a cell of emf 1 5 V and internal resistance 0 1 2 as shown The current drawn from the cell is diodes are ideal neet prep B diagram for OR gate 1 2 3 S S wing represents analog circun 8 High Yielding Test Series Part Test 7 1 Frequency of photon 2 Wavelength of photon 3 Intensity of photon 4 Stopping potential 175 Page 2 Contact Number 9667591930 8527521718 When monochromatic photons of wavelength 4000 A are incident on metal plate of work function 2 1 eV the stopping potential for the photo current is 1 1 V

The transistors provide good power amplification when they are used in 1 Common collector configuration 2 Common emitter configuration 3 Common base configuration 4 None of these

Example 14 5 In a Zener regulated power supply a Zener diode with 6 0 Vis used for regulation The load current is to be 4 0 mA and he unregulated input is 10 0 V What should be the value of series esistor R i 4mA ugh the Zener

Example 14 9 In Fig 14 31 a the VBB supply can be varied from OV to 5 0 V The Si transistor has Bac 250 and R 100 kn R 1 KQ Vcc 5 0V Assume that when the transistor is saturated V OV and VBE 0 8V Calculate a the minimum base current for which the transistor will reach saturation Hence b determine V when the transistor is switched on c find the ranges of V for which the transistor is switched off and switched on

lium arsenide phosphide is a semiconducting material having energy band gap of 2 eV The frequency of radiation is OPTIONS 2 83 X 10 14 Hz 5 83 X 10 14 Hz 4 83 X 10 14 Hz

conductor the fermi level lies 0 3 eV below the conduction band at 300 K What is the position of Fermi Level in intrinsic semiconductor OPTIONS near valence band near conduction band overlaps with conduction band

Semiconductor the fermi level lies 0 3 ev below the conduction band at 300 K If the temperature is increased to 330 K then new position of fermi level will be at OPTIONS 0 13 eV 0 23 eV 0 33 eV

figure strings are light Pulleys are massless and smooth System is released from rest In 0 3 seconds 2kg 1kg a work done on 2 kg block by gravity is 6J b work done on 2 kg block by string is 2J c work done on 1 kg block by gravity is 1 5J d work done on 1 kg block by string is 2 J 1 only a d are correct 3 only a b c are correct A body of mass 0 5 kg tu 4 All are correct 2 only b d are correct

The temperature dependence of resistances of Cu and undoped Si in the temperature range 300 400 K is best described by A B C Linear increase for Cu exponential decrease for Si Linear decrease for Cu linear decrease for Si Linear increase for Cu linear increase for Si Linear increase for Cu

8 For a semiconductor material the conventional flat band energy diagram is shown in the figure Y The variables Y X respectively are a distance energy c energy momentum Conduction band wwwwwwww Valence band X b momentum energy d energy distance

For the situation shown in the figure below mark out the correct statement s A Potential of the conductor is B Potential of the conductor is Hollow neutral conductor 9 4 d R q 4 d R D Potential at point B due to induced charges is C Potential of the conductor can t be determined as nature of distribution of induced charges is known SROOM qR 4TE d B d

A sequence detector is designed to detect precisely 3 digital inputs with overlapping sequences detectable For the sequence 1 0 1 and input data 1 1 0 1 0 0 1 1 0 1 0 1 1 0 of this detector what is the output 1 1 1 0 0 0 0 1 1 0 1 0 0

In an intrinsic semiconductor we doped boron with density 1 5 x 1018 atoms cm and posphorus with density 10 8 atoms cm then which type of semiconductor forms and what is the charge carrier density 1 P type 0 5 x 10 8 cm 3 2 N type 0 5 x 10 8 cm 3 3 P type 2 5 x 10 8 cm 3 4 N type 2 8 10 8 cm 8 9 R

Example 14 6 The current in the forward bias is known to be more mA than the current in the reverse bias UA What is the reason then to operate the photodiodes in reverse bias on the case of an n timo

n type semiconductors If acceptor impurity doping is higher than donor impurity doping then variation of charge density at junction is N eq 1 3 NA ND to not P ND 2 4 NA NA AP P

4 If resistivity of pure silicon is 3000 ohm m and the electron and hole motilities are 0 12m v s and 0 45 m v s respectively determine i The resistivity of a specimen of material when 10 9 atoms of phosphorus are added per m ii The resistivity of the specimen if further 2x10 9 boron atoms per m are also added

A rigid closed tank of volume 3 m contains 5 kg of wet steam at a pressure of 200 kPa The tank is heated until the steam becomes dry saturated Determine the final pressure and the heat transfer to the tank Ans 304 kPa 3346 kJ

For the situation in figure mark the correct statement Solid neutral conductor 9 lot d B H R Potential of the conductor is X Potential of the conductor is 9 4neod Both 2 and 3 9 4x eo d R Potential at point B due to the induced charges is qR 4neod d R