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31 Year NEET Previous Year Questions: Semiconductor Electronics - 4

25 Questions MCQ Test Physics 31 Years NEET Chapterwise Solved Papers | 31 Year NEET Previous Year Questions: Semiconductor Electronics - 4

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Attempt 31 Year NEET Previous Year Questions: Semiconductor Electronics - 4 | 25 questions in 50 minutes | Mock test for NEET preparation | Free important questions MCQ to study Physics 31 Years NEET Chapterwise Solved Papers for NEET Exam | Download free PDF with solutions

QUESTION: 1

p-n junction is said to be forward biased, when [1988]

A.
the positive pole of the battery is joined tothe p-semiconductor and negative pole tothe n-semiconductor
B.
the positive pole of the battery is joined tothe n-semiconductor and p-semiconductor
C.
the positive pole of the battery is connectedto n- semiconductor and p-semiconductor
D.
a mechanical force is applied in the forwarddirection

Solution:

For forward biasing of p-n junction, the
positive terminal of external battery is to be
connected to p-semiconductor and negative
terminal of battery to the n-semiconductor.

QUESTION: 2

At absolute zero, Si acts as [1988]

A.
non-metal
B.
metal
C.
insulator
D.
none of these

Solution:

Semiconductors are insulators at room
temperature

QUESTION: 3

When n-type semiconductor is heated [1989]

A.
number of electrons increases while that ofholes decreases
B.
number of holes increases while that ofelectrons decreases
C.
number of electrons and holes remain same
D.
number of electrons and holes increasesequally.

Solution:

Due to heating, when a free electron is
produced then simultaneously a hole is also
produced.

QUESTION: 4

Radiowaves of constant amplitude can begenerated with [1989]

A.
FET
B.
filter
C.
rectifier
D.
oscillator

Solution:

Radiowaves of constant amplitude can be
produced by using oscillator with proper
feedback.

QUESTION: 5

In a common base amplifier the phase differencebetween the input signal voltage and the outputvoltage is [1990]

A.
0
B.
π/4
C.
π/2
D.
π

Solution:

The phase difference between output
voltage and input signal voltage in common
base transistor or circuit is zero.

QUESTION: 6

When a triode is used as an amplifier the phasedifference between the input signal voltage andthe output is [1990]

A.
0
B.
π
C.
π/2
D.
π/4

Solution:

Voltage gain of an amplifier

The negative sign indicates that the output
voltage differs in phase from the input
voltage by 180°(or π). This holds for a pure
resistive load.

QUESTION: 7

The depletion layer in the p-n junction region iscaused by [1991]

A.
drift of holes
B.
diffusion of charge carriers
C.
migration of impurity ions
D.
drift of electrons

Solution:

The depletion layer in the p-n junction region
is caused by diffusion of charge carriers.

QUESTION: 8

The following truth table corresponds to the logic gate [1991]

A.
NAND
B.
OR
C.
AND
D.
XOR

Solution:

This truth table is of identity, X = A + B, hence
OR gate.

QUESTION: 9

To use a transistor as an amplifier [1991]

A.
the emitter base junction is forward biasedand the base collector junction is reversebiased
B.
no bias voltage is required
C.
both junctions are forward biased
D.
both junctions are reverse biased.

Solution:

To use a transistor as an amplifier the emitter
base junction is forward biased while the
collector base junction is reverse biased

QUESTION: 10

Which one of the following is the weakest kindof bonding in solids [1992]

A.
ionic
B.
metallic
C.
Vander Waal’s
D.
covalent

Solution:

Vander Waal’s bonding is the weakest
bonding in solids

QUESTION: 11

For amplification by a triode, the signal to beamplified is given to [1992]

A.
the cathode
B.
the grid
C.
the glass-envelope
D.
the anode

Solution:

The amplifying action of a triode is based on
the fact that a small change in grid voltage
causes a large change in plate current. The
AC input signal which is to be amplified is
superimposed on the grid potential.

QUESTION: 12

For an electronic valve, the plate current I andplate voltage V in the space charge limited regionare related as [1992]

A.
I is proportional to V^3/2
B.
I is proportional to V^2/3
C.
I is proportional to V
D.
I is proportional to V²

Solution:

According to Child’s Law,

QUESTION: 13

A piece of copper and other of germanium arecooled from the room temperature to 80 K, then [1993]

A.
resistance of each will increase
B.
resistance of copper will decrease
C.
resistance of copper will increase while thatof germanium will decrease
D.
resistance of copper will decrease while thatof germanium will increase

Solution:

Copper is a conductor, so, its resistance
decreases on decreasing temperature as
thermal agitation decreases whereas
germanium is semiconductor, therefore, on
decreasing temperature resistance increases.

QUESTION: 14

Diamond is very hard because [1993]

A.
it is a covalent solid
B.
it has large cohesive energy
C.
high melting point
D.
insoluble in all solvents

Solution:

Diamond is very hard due to large cohesive
energy.

QUESTION: 15

The part of the transistor which is heavily dopedto produce large number of majority carriers is [1993]

A.
emitter
B.
base
C.
collector
D.
any of the above depending upon the natureof transistor

Solution:

The function of emitter is to supply the
majority carriers. So, it is heavily doped

QUESTION: 16

An oscillator is nothing but an amplifer with [1994]

A.
positive feedback
B.
negative feedback
C.
large gain
D.
no feedback

Solution:

A positive feed back from output to input in
an amplifier provides oscillations of constant
amplitude.

QUESTION: 17

When a p-n junction diode is reverse biased theflow of current across the junction is mainly dueto [1994]

A.
diffusion of charges
B.
drift of charges
C.
depends on the nature of material
D.
both drift and diffusion of charges

Solution:

When p-n junction is reverse biased, the flow
of current is due to drifting of minority charge
carriers across the junction.

QUESTION: 18

In Fig., the input is across the terminals A and C and the output is across B and D. Then the output is

A.
zero
B.
same as the input
C.
half wave rectified
D.
full wave rectified

Solution:

It is the circuit of full wave rectifier.

QUESTION: 19

Which of the following gates corresponds tothe truth table given below? [1994]

A.
AND
B.
OR
C.
NAND
D.
XOR

Solution:

This truth table is of the identity, hence it is NAND gate.
Here, the output is high even if all inputs are low or one input is low.

QUESTION: 20

In the diagram, the input is across the terminals A and C and the output is across B and D. Then the output is [1994, 02]

A.
zero
B.
same as the input
C.
full wave rectifier
D.
half wave rectifier

Solution:

The given circuit is a circuit of full wave
rectifier.

QUESTION: 21

Which of the following, when added as animpurity, into the silicon, produces n-type semiconductor? [1995]

A.
Phosphorous
B.
Aluminium
C.
Magnesium
D.
Both b and c

Solution:

Phosphorous (P) is pentavalent and silicon
is tetravalent. Therefore, when silicon is
doped with pentavalent impurity, it forms a
n-type semiconductor.

QUESTION: 22

The current gain for a transistor working ascommon-base amplifier is 0.96. If the emittercurrent is 7.2 mA, then the base current is [1996]

A.
0.29 mA
B.
0.35 mA
C.
0.39 mA
D.
0.43 mA

Solution:

Current gain (α) = 0.96

QUESTION: 23

When an n–p–n transistor is used as an amplifierthen [1996]

A.
the electrons flow from emitter to collector
B.
the holes flow from emitter to collector
C.
the electrons flow from collector to emitter
D.
the electrons flow from battery to emitter

Solution:

In an n-p-n transistor, the charge carriers,
are free electrons in the transistor as well as
in external circuit; these electrons flow from
emitter to collector

QUESTION: 24

When arsenic is added as an impurity to silicon,the resulting material is [1996]

A.
n-type semiconductor
B.
p-type semiconductor
C.
n-type conductor
D.
insulator

Solution:

Arsenic contains 5 electrons in its outermost
shell. When Arsenic is mixed with silicon
there is one electron extra in silicon crystal.
Hence, such type of semi conductor is ntype
semi conductor

QUESTION: 25

To obtain a p-type germanium semiconductor,it must be doped with [1997]