Semiconductors Questions and Answers

4 Which of the following statements is incorrect for the depletion region of a diode a There the mobile charges exist b Equal number of holes and electrons exist making the region neutral c Recombination of holes and electrons has taken place d None of these diode

5 A dielectric slab fills the space between the plates of a parallel plate capacitor The magnitude of the bound charge on the slab is 75 of the magnitude of the free charge on the plates The capacitance is 480 F and the maximum charge that can be stored on the capacitor is 240 L Emax where Emax is the breakdown field Choose the CORRECT statement s A The dielectric constant for the dielectric slab is 4 B Without the dielectric the capacitance of the capacitor would be 360 F C The plate area is 60 L D If the dielectric slab is having the same area as the capacitor plate but the width half that of the capacitor the capacitance would be 192 F

An FM transmission has a frequency deviation of 18 75 kHz percent modulation if it is broadcast i in the 88 108 MHz band ii as a portion of a T V broadcast are respectively A skipped B C 25 75 75 75 33 3 66 6 MY

The clock frequency applied to the digital circuit shown in the figure below is 1KHz If the initial state of the output of the flip flop is 0 the frequency of the output waveform Q in KHz is 1 0 25 05 D X Cik T

A dual slope analog to digital converter uses an N bit counter When the input signal Va is being integrated the counter is allowed to count up to a value 1 Equal to 2N 2 2 Equal to 2N 1 3 Proportional to Va Inversely proportional to V

The circuit has two oppositely connected ideal diodes in parallel What is the current flowing in the circuit VL 12V Question Type Single Correct Type 1 1 71 A 22 00 A 422 wwww 3 2 31 A D 3 Q 2 Q

96 When NPN transistor is used as an amplifier then 1 Electrons move from collector to base 2 Holes move from collector to base 3 Holes move from base to collector 4 Electrons move from emitter to base

belled Reason R Select the correct answer to these ques tions from the codes a b c Note For question numbers 13 and 14 two statements are given one labelled Assertion A and the other labelled Reason R Select the correct answer to these questions from the codes a b c and d as given below a Both A and R are true and R is correct explanation of the assertion A b Both A and R are true but R is not the correct explanation of the assertion c A is true but R is false d A is false but R is true 13 Assertion A Following are the members of a homologous series CH OH CH CH OH CH CH CH OH Reason R A series of compounds with same functional group but differing by CH unit is called a homologous series 14 Assertion A Alloys are commonly used in electrical heating devices like electric iron and heater Reason R Resistivity of an alloy is generally higher than that of its constituent metals but the alloys have low melting points then their constituent metals Note For question numbers 13 and 14 two statements are given one labelled Assertion D Galant 1 1

In semiconductors at room temperature 2004 a the conduction band is completely empty b the valence band is partially empty and the conduction band is partially filled c the valence band is completely filled and the conduction band is partially filled the valence band is completely filled

8 You are given several identical resistors each of value 50 and each capable of carrying a maximum current of 2A It is required to make a suitable combination of these resistances to produce a resistance of 2 502 which can carry current of 4A The minimum number of resistances required for this job is 1 2 2 4 3 6 4 8

90 In a p n junction depletion region contains 1 No charges at all 2 Equal number of conduction electrons a holes 3 Equal number of donor and acceptor ions 4 More conduction holes than electrons

4 Consider an NPN transistor amplifies in common emitter configuration the current gain of the transistor is 100 If the collector current changes by 1mA what will be change in emitter current 1 1 1 mA 2 1 01 mA 4 10 mA A

Problem 9 A junction diode has a resistance of 25 2 wher forward biased and 2500 2 when reverse biased The current in the arrangement shown in figure will be 5V OV 1 A 15 3 A 100 wwwww 2 4 1 25 A 1 A 480

For the circuit shown in figure find i the output voltage ii the voltage drop across ries resistance iii current through Zener diode iv current through load resistor 4 R 5kn w 120 V I 12 50 V 10 k 4

The carrier frequency in an FM modulator is 500 kHz If the modulating frequency is 3 kHz What are the upper sideband and two lower sideband frequencies A 503 497 494 kHz B 506 494 488 kHz

What fraction of tetravalent atom must be replaced with pentavalent atom so as to 10 2 m 3 increase its number density of about by a factor of 10000 density of tetravalent is 2 33 g cm molar mass is 28 1 g mol density of pentavalent is 4 28 g cm 3 molar mass is 17 3 g mol A B C skipped One in five million One in five hundred million One in five thousand billion One in five thousand million

With respect to the potential of emitter base and collector a NPN transistor conducts when 1 both collector and emitter are positive with respect to the base 2 collector is positive and emitter is negative with respect to the base 3 collector is positive and emitter is at same potential as the base 4 both collector and emitter are negative with respect to the base

Illustration 10 For a common emitter amplifier current gain 50 If the emitter current is 6 6 mA calculate the collector and base current Also calculate current gain when emitter is working as common base amplifier

25 Figure shows two convex lenses A and B each made up of three different transparent materi als The number of images formed of an object kept on the principal axis of each lens will be 1 3 and 3 3 1 and 1 2 3 and 1 4 3 and 2

Q No 13 Convert 1 01 0 0100 binary number into decimal equivalent number A 10 25 B 18 1 C 10 01 D 10 01

llector current to base current of a transistor is B B x X 1 La 1 1 B 1 B 1 B Question Type MC Question ID 964

articular semiconductor in equilibrium has 1 x 10 cm donor atoms 107 cm acceptor atoms If the intrinsic carrier density n of the iconductor is 10 cm then the electron density in it will be n 11 X 10 11 x 10 6 106 le ni nw 24 10 1017 10 x10 6 10 7 cm A 10 cm 10 B 10 C 1 1

40 A p n junction D shown in the figure can act as a rectifier when an alternating current source V is connected in the circuit 1 D 3 The current in the resistor can be shown by 1 2 www 4 R st

Analyze how LED is different from pn diode Justify the role of P N Junction diode as LED

A 1 1 2 3 0 B 1 3LED Y OR R The correct Boolean operation repres circuit diagram drawn is NOR AND O

The following Boolean Function is equivalent to F X Y Z 0 2 4 5 6 A XY Z B Z XY 7

4 The output of the following circuit can be summarised as AD B 1 OR 3 XOR D Do 7 4 A B 1 Bo 01 0 1 0 0 Da 1 00 0 0 2 AND 4 XNOR 9 2

An n channel JFET having a pinch off voltage of 3 5V has a saturation current of 2 3 mA when VGs 1 V What is its saturation current when a VGS 0V and b Vcs 2 V

0 What volume of air at 1 atm and 273 K containing 21 of oxygen by volume is requirec completely burn sulphur Sg present in 200 g of sample which contains 20 inert mate which does not burn Sulphur burns according to the reaction 1 Sg s O g SO g 8

In an unbiased n p junction electrons diffuse from n region to p region because 1 electrons travel across the junction due to potential difference 2 electron concentration in n region is more as compared to that in p region 3 holes in p region attract them 4 only electros move from n to p region and not the vice versa 2015

5 Identify the semiconductor devices whose characteristics are given below in the order 1 2 Resistance 3 4 V dark Illuminated c 1 Zener diode Simple diode Light dependent resistance Solar cell 2 Solar cell Light dependent resistance Zener diode Simple diode 3 Zener diode Solar cell Simple diode Light dependent resistance 4 Simple diode Zener diode Solar cell Light dependent resistance Intensity of light d 2016

For LED s to emit light in visible region of electromagnetic light it should have energy band gap in the range of 2014 1 0 1 eV to 0 4 eV 3 0 9 eV to 0 8 eV 2 0 5 eV to 0 8 eV 4 1 7 eV to 3 0 eV

then current gain a and B are For a CE amplifier current gain is 69 If the emitter current is 7 mA then calculate the base current and collect AIPMT Mains 2008 current

What is an SCR Define the following terms i Forward current rating ii Breakover voltage

Problem 2 A full wave rectifier is fed with ac mains of frequency 50 Hz What is the fundamental frequency of the ripple in the output current 1 25 Hz 3 75 Hz 2 4 50 Hz 100 Hz

When npn transistor is used as an amplifier then a electrons move from collector to base b holes move from base to emitter c electrons move from base to collector d electrons move from emitter to base 1006

29 For transistor action a Base emitter and collector regions should have similar size and doping concentrations JOUR b The base region must be very thin and lightly doped c The emitter base junction is forward biased and base collector junction is reverse biased d Both the emitter base junction as well as the base collector junction are forward biased Which one of the following pairs of statements is correct 1 S 1 a b 3 c d 2 b c 4 n

If the forward voltage in a diode is increased the width of the depletion region a Fluctuates Increases b d Decreases Remains the same

36 The increase in the width of the depletion region in a p n junction diode is due to s forward bias only reverse bias only both forward bias and reverse bias increase in forward current 2 3 4

1 The solids which have the negative temperature coefficient of resistance are metals insulators only semiconductors only 4 insulators and semiconductors 1 2

The truth table for the circuit shown in the figure is 2 5 V Ao Bo ABY 000 1 01 0 100 1 1 1 ABY 000 3 01 101 K Diode 1 Diode 2 OY ABY 0 0 1 2 0 1 1 100 1 1 1 ABY 001 4 0 1 0 10 1 C

5 The truth table for the circuit shown will be X D 1 Z 0 0 0 0 1 0 100 1 1 1 x y z 000 b 011 1 0 1 1 2011 0 2 4 o Z 0 0 0 0 1 1 10 1 1 1 1 y z 0 0 1 0 1 0 100 1 1 1 Z

5V 6KQ 9V B BE g t 0 IKO 1 22 2Kn For the given transistor circuit V 0 7 V Find I E 1 3 7 mA 3 1 8 mA 2 2 2 mA 4 1 5 mA

4 In the circuit shown in figure find the value of Rc RB HH 20k 100 k T www H 20 KQ ww E Rc 7 8 k Vc RE ww Rc C Vcc 12V A 12V A B 100 VBE 0 5 V VCE 3V

0 A 1 0 B 1 R adi prib loLED Y R The correct Boolean operation represented by the circuit diagram drawn is 1 AND 3 NAND 2YOR 4 NOR

In the following common emitter VCE 7V VBE negligible Rc 2k2 then IB 1B Vic ww RB 1 0 01 mA B Rc E 15V 2 0 04 mA 4003 mA

In the given circuit Zener diode regulated voltage is taken across load resistance 6 k22 if current through 0 5 k resistor is 4 mA then current in load resistor is V 10 V 1 2 67 mA 0 5 KQ www www 2 4 mA 1 2 mA 6 KQ

Select the correct match A A B A B B A B A B C A B A B A B 1 A and C 2 B and C 3 A and B 4 A B C

A common emitter transistor amplifier is connected with a load resistance of 6 ks When a small a c signal of 15 mV is added to the base emitter voltage the alternating base current is 20 A and the alternating collector current is 1 8 mA What is the voltage gain of the amplifier A 90 B 640 C 900 D 720

25 Find the currents through the resistances in the circuits shown in figure 45 E3 K 2V 252 Imm 2V 292 0 2 V 2 V 292 KH 252