Assignment No 10 Semiconctor Devices

8/13/2019 Assignment No 10 Semiconctor Devices

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ASSIGNMENT-10

SEMICONDUCTOR DEVICESGUIDE LINE FOR PREPARING CBSE (PHYSICS) EXAMINATION THROUGH

PREVIOUS YEARS QUESTIONS OF CBSE

MARKED WITH STARS ( )THESE QUESTIONS ALSO APPEARED OFTEN IN QUATERLY, HALFYEARLY AND PRE-

BOARD EXAINATION S OF DIFFERENT PUBLIC SCHOOLS OF DELHI.

(Generally five-, three-, two- and one- marks questions are generated from the theory andderivation part of the questions mentioned below including final formula)

1.

2. Discuss the energy band in solids.***

3. What is hole in a semiconductor? What is the charge on it?**4. What are energy bands? How are these formed? Distinguish between metals, insulators and

semiconductors on the basis of their energy bands.( CBSE2004; MATA DIE P S;ANDHRA EDUC. SOC)

. What is the order of energy ga! in a semiconductor?*** "#ns$ %he energy ga! in a semiconductor is of the order of 1 e&'

(. How does the conducti)ity of a semiconductor change with tem!erature? "#ns$%he

conducti)ity of a semiconductor increases with increase of tem!erature.'**. +i)e the ratio of number of holes and number of conduction electrons in an intrinsic

semiconductor."#ns$ atio 1:1'****

-. What is an etrinsic semiconductor? Distinguish between its ty!es.******

/. How can !ure Gebe con)erted into 0inty!e semiconductor and 0iipty!esemiconductor.***

1. What ty!e of etrinsic semiconductor is formed when 0i germanium is do!ed indium and

0ii silicon is do!ed with bismuth?"#ns$0i nty!e semiconductor 0iipty!e semiconductor.'***

11. 5ame one im!urity each, which when added to !ure Si, !roduces 0inty!e semiconductorand 0iipty!e semiconductor. ***

12. How does the energy ga! in a semiconductor )ary, when do!ed with a !enta)alentim!urity? "#ns$ %he energy ga! decreases by miing !enta)alent im!urity.'***

13. 6n a nty!e semiconductor, the number of free electrons is greater than the number of holes .

Does it ha)e net negati)e charge? Why? ***14. Why is the conducti)ity of nty!e semiconductor greater than that of thepty!e

semiconductor e)en when both of these ha)e same le)el of do!ing?***

1. 5ame two factors on which electrical conducti)ity of a !ure semiconductor at a gi)en

tem!erature de!ends.***1(. +i)e the ratio of the number of holes and number of concentration of electrons in intrinsic

semiconductor.**1. 6s the ratio of number of holes and number of conduction electrons in ap ty!e

semiconductor more than, less than or e7ual to 1 ?**1-. How does the energy ga! of an intrinsic semiconductor )ary, when do!ed with a tri)alent

im!urity?**1/. How does the conductance of semiconductor material change with rise in tem!erature?**2. Draw energy band diagram for a 0ipty!e etrinsic semiconductor, 0ii n ty!e etrinsic

semiconductor and 0ii intrinsic semiconductor.***

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21. Distinguish betweenn-ty!e andpty!e semiconductor on the basis of energy diagram.**

22. 6n semiconductor, the concentration of electrons is - 113cm3and hole 112cm3. 6s it

apty!e ornty!e semiconductor? "#ns$%he concentration of electron is more than the

concentration of holes, therefore the etrinsic semiconductor is n-ty!e.'**

23. # semiconductor has e7ual electron and hole concentration of 2 1-8 m3. 9n do!ing, hole

concentration increases to 4 11

8 m3

$ 0iWhat ty!e of semiconductor is obtained afterdo!ing ? 0ii:alculate new electron concentration in the semiconductor and 0iii How does

energy ga! )ary with do!ing.*****

24. +i)e the ratio of the number of holes and the number of conduction electron in an intrinsicsemiconductor.**

2. %he ratio of the number density, of free electrons to holes 0ne/ nh, for three different

materialsA,B and Care e7ual to one, less than one and more than one res!ecti)ely. 5ame

the ty!e of semiconductor to whichA,Band : belong. Draw labeled energy band diagramsfor the three materials.***

2(. # co!!er stri!, semiconductor stri! and a milliammeter is connected in series with a cell.

What will ha!!en to the milliammeter reading if 0i when only semiconductor stri! is

heated ***and 0ii when only co!!er stri! is heated.

P N- jun!"#n $"#$%&'%!""%'& "+,! %"!"n+ $"#$% (ED) P,#!#$"#$%

2. +i)e the )alue of the threshold )oltage for a 0i ;ilicon diode and 0ii +ermanium diode.(**ANDHRA EDUC. SOC)

2-. Draw the symbolic notation for a p-n con)entional ightemitting diode0>D, @hotodiode. 6n which mode these diodes are used***

2/. Howpn


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con)entional diode im!urity concentration is moderate. 6n =ener diode the !otential barrier width is )ery small

and the electric field eisting at the


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. # transistor am!lifier has , load resistanceRL= ohmand in!utresistanceRi

ohm. Eind the )oltage am!lification. ( BA BH P S)

(. 6n a silicon transistor the base current is changed by 2 #. %his results in a change of .2

& in base to emitter )oltage and a change of 2 m# in the collector current:0i Eind the in!ut

resistance, a.c and transconductance of the transistor and 0ii 6f the transistor is used as an

am!lifier with the load resistance ohm, what is the )oltage gain of the am!lifier?(R3ANINT P SCH)

. %he in!ut resistance of a silicon transistor is (( ohm. 6ts base current is changed by 1 #

which results in change of collector current by 2 m#. %his transistor is used as common

emitter am!lifier with a load resistance of ohm. :alculate$

0i a.c,0ii %ransconductance and 0iii &oltage gain of the am!lifier.(MA3UR P S)

-. 0aDraw a circuit diagram of a common emitter am!lifier using n-p-ntransistor. ;how in!ut

and out!ut )oltages gra!hically.(CBSE 200/)

0b %he current gain for common emitter am!lifier is /. 6f the emitter current is (. m#,find$ 0i base current and 0ii collector current.(CBSE 200/)

/. Eor npntransistor in the commonemitter configuration, draw a labeled circuit diagram of

an arrangement for measuring the collector current as a function of collectoremitter )oltagefor at least two different )alues of base current. Draw the sha!es of the cur)es obtained.Define the terms$ 0i out!ut resistance and 0ii current am!lification factor.(*****CBSE

2004)

(. Draw a circuit diagram of use ofnpntransistor as an am!lifier in common emitterconfiguration. %he in!ut resistance of a transistor is 1 ohm. 9n changing its base current

by 1 # , the collector current increased by 2 m#. 6f a load resistance of ohm is used

in the circuit, calculate:0i the current gain and 0ii )oltage gain of the am!lifier.(CBSE

200/)

(1. Why the base region of a transistor is usually made thin? 6n commonemitter mode of

transistor, d.c. current gain is 2, the emitter current is m#. :alculate 0i base current and

0ii collector current (CBSE)(2. Draw the circuit diagram to show the use of a transistor as an oscillator. ;tate how the

!ositi)e feedbacA is !ro)ided in the circuit.( CBSE 2004&200/ BA BH P S ; D P SNOIDA; DAV PB SC& D3AND VHR)

#+" +6!%

(3. Write the logic symbol and truthtable of anAND& OR gate. !lain how it can be realiBed

by using two


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figure are used as two in!uts

of 0iAND gate and 0ii OR

gate. Eind the out!utwa)eforms.**

(/. Write the truth table and draw

the logic symbol of the gatefor the circuit gi)en below$(CBSE 2007)

0a

0b

. %wo signalsAandBshown in

figure are used as two in!uts

of 0iNOR gate and 0ii

NAND gate. Eind the out!utwa)eforms.**

1. %he gi)en in!utsA,Bare fed to

a 2in!ut of 5#5D gate. Draw

the out!ut wa)e form of thegate. (CBSE 2007)

3 %he in!utsAandB are in)erted by using two 59% gates and their in!uts are fed to the

59 gate as shown below

#nalyBe the action of the gates 01 and 02 and identify the logic gate of the

com!lete circuit so obtained. (CBSE 2007)


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Assignment No 10 Semiconctor Devices

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