IISER 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
Conduction electrons have more mobility than holes because they
- (a)
are lighter
- (b)
experience collisions less frequently
- (c)
need less energy to move them
- (d)
have negative charge
In a semiconducting material,
- (a)
both holes and electrons move in valency band
- (b)
both holes and electrons move in conduction band
- (c)
holes move in valency band whereas free electrons move in conduction band
- (d)
holes move in conduction band whereas free electrons move in valency band
Sodium chloride is
- (a)
ionic crystal
- (b)
covalent crystal
- (c)
semi-conductor
- (d)
insulator
Solid paraffin and sulphur have
- (a)
metalic binding forces
- (b)
ionic binding forces
- (c)
covalent binding forces
- (d)
van der Wala's binding forces
Ice has
- (a)
ionic binding
- (b)
covalent binding
- (c)
metallic bonding
- (d)
van der Waals' binding
A bcc crystal has a lattice parameter of \(3.4\mathring { A } \).Its atomic radius is
- (a)
\(3.10\mathring { A } \)
- (b)
\(1.47\mathring { A } \)
- (c)
\(2.60\mathring { A } \)
- (d)
None of the above
The structure of NaCl is
- (a)
superposition of two fcc lattices
- (b)
having coordination number for same kind of ions is 12
- (c)
having coordination number for opposite kinds of ions is 6
- (d)
all of the above
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)
\({10}^{30}kg {m}^{-3}\)
The type of binding in germanium crystal is
- (a)
ionic
- (b)
metallic
- (c)
covalent
- (d)
van der Waals
Single crystals are, in general
- (a)
anisotropic
- (b)
dielectric
- (c)
homogenous
- (d)
all of the above
The weakest bonding is
- (a)
ionic
- (b)
covalent
- (c)
metallic
- (d)
van der Waals
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
In a pn-junction with open ends
- (a)
holes and conduction electrons systematically go from the p-side to the n-side and from n-side to the p-side respectively
- (b)
there is no net charge transfer between the two sides
- (c)
there is a constant electric field near the junction
- (d)
All of the above
The value of \(\beta\)
- (a)
is always less than 1
- (b)
lies between 50 and 150
- (c)
is always greater than 150
- (d)
is always 100
In a transistor (\(\beta=45\)), the voltage across \(5 K\Omega\) load resistance in collector circuit is 5V. the base current is
- (a)
0.022 mA
- (b)
0.978 mA
- (c)
1.0 mA
- (d)
2.5 mA
In a transistor
- (a)
The emitter has the least concentration of impurity
- (b)
the collector has the least concertration of impurity
- (c)
the base has the least concentration of impurity
- (d)
the concentration of inpurity is uniform in all the regions, namely,emitter,collector,and base
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
Resistivity of a semiconductor depends on
- (a)
shape of semiconductor
- (b)
atomic nature of semiconductor
- (c)
length of semiconductor
- (d)
shape and atomic nature of semiconductor
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
N-type germanium is obtained on doping intrinsic germanium by
- (a)
aluminium
- (b)
boron
- (c)
phosphorus
- (d)
gold
Zener diode is used for
- (a)
rectification
- (b)
stabilisation
- (c)
amplification
- (d)
oscillation
In a halfwave rectifier, the r.m.s value of the a.c. component of the wave is
- (a)
equal to d.c value
- (b)
more than d.c value
- (c)
less than d.c value
- (d)
zero
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
The following truth table corresponds to the logic gate
A | B | x |
0 | 0 | 0 |
0 | 1 | 1 |
1 | 0 | 1 |
1 | 1 | 1 |
- (a)
NAND
- (b)
OR
- (c)
AND
- (d)
XOR
The band gap inGe and Si ineV respectively is
- (a)
0.7,1.1
- (b)
1.1,0.7
- (c)
1.1,0
- (d)
0,1.1
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
Which of the following statements is NOT ture?
- (a)
The resistance of intrinsic semiconductor decreases with increase of temperature
- (b)
Doping pure Si with trivalent impurities given p-type semiconductor
- (c)
The majority carriers in n-type semiconductors are holes
- (d)
A p-n junction can act as a semiconductor diode
A transistor is used in common emitter mode as an amplifier.then
A. the collector-emitter junction is forward biased
B. the collector-emitter junction is reverse biased
C. the output signal is connected in series with voltage applied to the collector-emitter junction
D. the output 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 C are correct
- (c)
if A and D are correct
- (d)
if B and D are correct