1
MCQ (Single Correct Answer)

AIPMT 2008

With which one of the following elements silicon should be doped so as to give p-type of semiconductor?
A
Selenium
B
Boron
C
Germanium
D
Arsenic

Explanation

The semiconductors formed by the introduction of impurity atoms containing one elecron less than the parent atoms of insulators are termed as p-type semiconductors. Therefore silicon containing 14 electrons has to be doped with boron containing 13 electrons to give a p-type semi-conductor.
2
MCQ (Single Correct Answer)

AIPMT 2007

If NaCl is doped with 10$$-$$4 mol% of SrCl2, the concentration of cation vacancies will be (NA = 6.02 $$ \times $$ 1023 mol$$-$$1)
A
6.02 $$ \times $$ 1016 mol$$-$$1
B
6.02 $$ \times $$ 1017 mol$$-$$1
C
6.02 $$ \times $$ 1014 mol$$-$$1
D
6.02 $$ \times $$ 1015 mol$$-$$1

Explanation

As each Sr2+ ion introduces one cation vacancy, therefore concentration of cation vacancies = mole % of SrCl2 added.

$$ \therefore $$ Concentration of cation vacancies

= 10–4 mole %

= $${{{{10}^{ - 4}}} \over {100}} \times 6.023 \times {10^{23}}$$

= $$6.023 \times {10^{23}}$$ $$ \times $$ 10-6

= $$6.023 \times {10^{17}}$$
3
MCQ (Single Correct Answer)

AIPMT 2007

The fraction of total volume occupied by the atoms present in a simple cube is
A
$${\pi \over {3\sqrt 2 }}$$
B
$${\pi \over {4\sqrt 2 }}$$
C
$${\pi \over 4}$$
D
$${\pi \over 6}$$

Explanation

The maximum properties of the available volume which may be filled by hard sphere in simple cubic arrangement is $${\pi \over 6}$$ or 0.52.
4
MCQ (Single Correct Answer)

AIPMT 2006

CsBr crystallises in a body centered cubic lattice. The unit cell length is 436.6 pm. Given that the atomic mass of Cs = 133 and that of Br = 80 amu and Avogadro number being 6.02 $$ \times $$ 1023 mol$$-$$1, the density of CsBr is
A
4.25 g/cm3
B
42.5 g/cm3
C
0.425 g/cm3
D
8.25 g/cm3

Explanation

Density of CsBr = $${{Z \times M} \over {V \times {N_A}}}$$

= $${{1 \times 213} \over {{{\left( {436.6 \times {{10}^{ - 10}}} \right)}^3} \times 6.023 \times {{10}^{23}}}}$$

= 4.25 g/cm3

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