24 - SOLIDS AND SEMI-CONDUCTOR DEVICES (Answers at the end of all questions}

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1 ) In a common base output voltage is

amplifier, the phase difference between the Input signal voltage and

(a) 11: (b) 'It:/ 4 (c) ~/2 (d) zero

2 ) In a full wave rectifier, circuit operating from 50 Hz mains frequency, frequency in the ripple would be (a) 25 Hz ( b I 50 Hz ( c I 70.7 Hz ( d I 100 Hz

3 ) When npn transistor is used as an amplifier ( a ) electrons move from base to collector ( c ) electrons move from collector to base

[ AIEEE 2005 }

2005}

4) For a transistor amplifier in common emitter configura~r.,l~d impedance of 1 M ( ht = 50 and h.,., = 25 IJA IV ), the current gain i , '!{J (a} -5.2 (b) -15.7 (c) -24.8 (d) 48.7. { AIEEE 2004 I

5) temperature to 80 K.

( a ) each of these increases ( b ) h o se decreases ( c ) copper strip increases and that aniUm decreases The resistance of ~

( d ) copper strip decreases and o nlum increases [ AIEEE 2004, 2003 I

6 I The lids is due to ( a ) Heisenberg's uncertain ( c ) Bohr's correspondenc

( b ) Pauli's exclusion principle ( d ) Boltzmann's law

7 ) When p-n junction (a I ( b I (c) both the (d) both

and barrier eight is Increased widened and barrier height is reduced

nJiriogicn and barrier height are reduced region and barrier height are Increased

I AIEEE 2004 I

I AIEEE 2004 I

8 I The variation of resistance with temperature in a metal and a rises essentially due to the difference in

bonding ( b 1 crystal structure g mechanism with temperature ( d } no. of charge carriers with temp.

I AIEEE 2003 I

middle of the depletion layer of a reverse biased p-n junction, the the potential is zero ( b ) electric field is zero potential is maximum ( d ) electric field is maximum 1 AlE EE 2003 1

10) In a p-n junction, the depletion layer consists of ( a ) electrons ( b ) protons ( c ) mobile ions ( d 1 immobile ions

11 ) In forward bias, the width of otential barrier in p-n )unction diode ( a 1 increases ( b ) decreases ( c ) remans constant

( d ) first increases, then decreases

[ AIEEE 2002 I

[ AIEEE 2002 }

24 - SOLIDS AND SEMI-CONDUCTOR DEVICES (Answers at the end of all questions}

12 1 When a potential difference is applied across, the current passing through, ( a 1 an insulator at 0 K is zero ( b 1 a semiconductor at 0 K Is zero ( c 1 a metal at 0 K is finite ( d 1 a p-n diode at 300 K is finite if it is reverse biased

13 1 A transistor is used in common emitter mode as ( a 1 the base emitter junction is forward biased ( b 1 the base emitter junction is reverse biased ( c 1 the Input signal is connected In series with the

emitter junction ( d } the input signal is connected in series with

connector junction

14 1 In a p-n junction diode not connected to any

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9991

the base

(a I ( b I ( c I side to the p-type ( d I from the p-type side to the n-type

(liT 1998] 15 1 Which of the

I liT 1997 I 16)

( b 1 ionic solids [liT 1996]

17 the output is shown in the figure. The

v

t

(b) A, C I c I B, 0 ( d} A, B, C, 0 [liT 19961

18 1 Read the following statements carefully: Y : The resistivity of a semiconductor decreases with increase of temperature Z : In a conducting solid, the rate of collisions between free electrons and ions increases

with increase of temperature ( a 1 Y is true but Z is false ( c 1 Both Y and Z are true

( b 1 Y is false but Z is true ( d 1 Y is true and Z is the correct reason for Y

(liT 1993]

24 - SOLIDS AND SEMI-CONDUCTOR DEVICES (Answers at the end of all questions}

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19 1 In an n-p-n transistor circuit, the collector current Is 10 mA. If 90% of the electrons emitted reach the collector (a 1 the emitter current wll be 9 mA (b) the emitter current will be 11 mA ( c 1 the base current will be 1 mA ( d 1 the base current will be -1 mA

20 } Two Identical p-n junctions may be connected in series with a battery in three ways as shown in the figure. The potential drops Circuit 1

across the two n-p junctions are equal in 1 + ( a 1 circuit 1 and circuit 2 ( b 1 circuIt 2 and cir i ( c 1 circuIt 3 and circuit 1 ( d 1 circuit 1 on I {liT 1989)

21 1 A piece of copper and another of from room temperature to so K. The resistance of ( a 1 each of them increases ( b ) ~ decreases ( c 1 copper increases and germanium rea ( d 1 copper decreases and 1 eas s [liT 1988)

22 ) The impurity atoms with ilicon should be doped to make a p-type semiconductor are those of (a 1 phosphorous ( b~n ( c 1 antimony

23 1 Select the correct state r the following: ( a 1 A diode can be a rectifier.

( c I aluminium [Ill 1988)

( b 1 A triode cannot as a rectifier.

( d 1 The linear I of the I - V characteristic of a triode is used for amplification witho t dist . [ Ill 1984 )

.. ~~listtnce of a triode valve is 3 x 103 ohm and its mutual conductance is volt. The amplification factor of the triode is

(b) 4.5 (c) 0.45 ( d I 2 X 106 1 111 1983, 1981 1

Answers