Physics - Solids and Semiconductor Devices
Exam Duration: 45 Mins Total Questions : 30
Copper has no hole current because
- (a)
it has large forbidden gap
- (b)
it has no valency band
- (c)
it has full electron gas
- (d)
it has overlapping valency and conduction bands
Sodium chloride is
- (a)
ionic crystal
- (b)
covalent crystal
- (c)
semi-conductor
- (d)
insulator
Ice has
- (a)
ionic binding
- (b)
covalent binding
- (c)
metallic bonding
- (d)
van der Waals' binding
the number of lattice points per unit cell in copper lattice is
- (a)
1
- (b)
2
- (c)
4
- (d)
14
A crystal has fcc structure.Its molecular weight is 62.5 and the lattice constant is \(4\mathring {A}\).its density is of the order of
- (a)
\({10}^{3}kg {m}^{-3}\)
- (b)
\({10}^{4}kg {m}^{-3}\)
- (c)
\({10}^{23}kg {m}^{-3}\)
- (d)
\({10}^{30}kg {m}^{-3}\)
Which of the following has greatest packing fraction?
- (a)
simple cubic
- (b)
body-centred cubic
- (c)
face-centred cubic
- (d)
all have equal packing fraction
The forbidden band in germanium at 0 K is
- (a)
0.785 eV
- (b)
1.21 eV
- (c)
1.00 eV
- (d)
0.01 eV
The pure semiconductor has
- (a)
an infinite resistance at \({ 0 }^{ \circ }\)C
- (b)
a finite resistance which does not change with temperature
- (c)
a finite resistance which decreases with temperature
- (d)
a finite resistance which increases with temperature
When we apply reverse bias to a junction diode it
- (a)
lowers the potential barrier
- (b)
raises the potential barrier
- (c)
Increases the majority carrier current
- (d)
Increases the minority carrier current
In case of diamond, the forbidden gap is about
- (a)
0.8 eV
- (b)
1. eV
- (c)
6.0 eV
- (d)
8.2 eV
In a p-n junction diode at high value of reverse bias the current rises sharply.The value of reverse bias is known as
- (a)
cut-off voltage
- (b)
zener voltage
- (c)
inverse voltage
- (d)
critical voltage
When a p-n junction is reverse biased, the flow of current across the junction is mainly due to
- (a)
diffusion of charge carriers
- (b)
drift of charges
- (c)
both drift and diffusion of the charges
- (d)
depends upon the nature of material
Read the following statements:
Y: The resistivity of a semi conductor decreases with increase of temperature
Z: In a conducting solid, the rate of collisions between free electrons and ions increases with increase of temperature.
select the correct statements from the following:
- (a)
Y is true but Z is false
- (b)
Y is false but Z is true
- (c)
Both Y and Z is true
- (d)
Y is corect and Z is the correct reason for Y
The energy gap of a silicons is 1.14 eV.The maximum wavelength at which silicon absorbs energy is
- (a)
10.888\(\mathring { A } \)
- (b)
\(108.88\mathring { A } \)
- (c)
\(1088.8\mathring { A } \)
- (d)
\(10888\mathring { A } \)
The typical ionisation energy of a donor in silicon is
- (a)
10.0 eV
- (b)
1.0 eV
- (c)
0.1 eV
- (d)
0.001 eV
In p-n junction diode the reverse saturation current is \({10}^{-5}A\)at \(27^{ \circ }C\). the forward current for a voltage of 0.2 V is [exp(7.62)=2038.6; k=\(1.4\times{10}^{-23} J{K}^{-1}\)]
- (a)
\(2037.6\times{10}^{-3} A\)
- (b)
\(203.76\times{10}^{-3} A\)
- (c)
\(20.376\times{10}^{-3} A\)
- (d)
\(2.0376\times{10}^{-3} A\)
The part of a transistor which is heavily doped to produce a large number of majority carriers is
- (a)
base
- (b)
emitter
- (c)
collector
- (d)
none of these
Three semiconductors are arranged in the increasing order of their energy gap as follows.The correct arrangement is
- (a)
tellurium,germanium,sillicon
- (b)
tellurium,silicon,germanium
- (c)
silicon,germanium,tellurium
- (d)
silicon,tellurium, germanium
In p-n jundtions , the barrier potential offers resistance to
- (a)
free electrons in n region and holes in p-region
- (b)
free electrons in p region and holes in n-region
- (c)
only free electrons in n-region
- (d)
only holes in p-region
In a full wave rectifier with input frequency 50Hz, the ripple in the output is mainly of the frequency(in Hz)
- (a)
25
- (b)
50
- (c)
100
- (d)
None of these
In Boolean Algebra A+A is equal to
- (a)
0
- (b)
1
- (c)
A
- (d)
2A
Which one of the following gates correspond to the truth table given below?
A | B | y |
1 | 1 | 0 |
1 | 0 | 1 |
0 | 1 | 1 |
0 | 0 | 1 |
- (a)
XOR
- (b)
OR
- (c)
NAND
- (d)
NOR
Consider the two inputs of AND gate.Which of the following enteries in the truth table correspond to its working?
A | B | y | |
(i) | 0 | 1 | 0 |
(ii) | 1 | 0 | 0 |
(iii) | 1 | 1 | 1 |
(iv) | 0 | 0 | 1 |
- (a)
all
- (b)
(i) and (ii) only
- (c)
(i),(ii) and (iii) only
- (d)
(i),(iii) and (iv) only
A logic gates is an electronic circuit which
- (a)
makes logic decisions
- (b)
allows electrons flow only in one direction
- (c)
works binary algebra
- (d)
alternates between 0 and 1 values
Two wires P and Q made up of different materials have some resistance at room temperatures.When heated,resistance of P increases and that of Q decreases.We may conclude that
- (a)
P and Q are both conductors but because of being made of different materials it happens so.
- (b)
P is n-type semiconductor and Q is p-type semiconductor
- (c)
P is semiconductor and Q is conductor
- (d)
P is conductor and Q is semiconductor
Holes are majority charge carriers in
- (a)
intrinsic semiconductor
- (b)
ionic solids
- (c)
p-type semiconductor
- (d)
metals
A transistor is used in common emitter mode as an amplifier.Then
A. the base -emitter junction is forward biased
B. the base-emitter junction is reverse biased
C. the input signal is connected in series with the voltage applied to the base-emitter junction
D. the input signal is connected in series with the voltage applied to bias the base-collector junction
- (a)
if A and C are correct
- (b)
if B and D are correct
- (c)
if A is correct
- (d)
if B is correct