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Multiple choice chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

If we mix a pentavalent impurity in a crystal lattice of germanium, what type of semiconductor formation will occur? 

  1. p-type

  2. n-type

  3. Both A and B

  4. None of the the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Silicon and germanium belong to group 14 of the periodic table and have four valence electrons each. In their crystals each atom forms four covalent bonds with its neighbours. When doped with a group 15 element like P or As, which contains five valence electrons, they occupy some of the lattice sites in silicon or germanium crystal. Four out of five electrons are used in the formation of four covalent bonds with the four neighbouring silicon atoms. The fifth electron is extra and becomes delocalised.These delocalised electrons increase the conductivity of doped silicon(or germanium). Here the increase in conductivity is due to the negatively charged electron, hence silicon doped with electron-rich impurity is called n-type semiconductor.

Multiple choice chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

Select the correct statement.

  1. LiF and MgO are isostructural and also isodimensional, but a crystal of MgO is much harder than one of LiF.
  2. The thermal stability of the isomorphous sulphates of $Ca^{2+}, Sr^{2+}$ and $Ba^{2+}$ w.r.t. decomposition into metal oxide and sulphur trioxide increases in the order $CaSO _4, SrSO _4, BaSO _4$.

  3. Both (a) and (b)

  4. None of above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

LiF and MgO are isostructural and also isodimensional, but a crystal of MgO is much harder than one of LiF because of electronic repulsions in the small sized LiF.
Thermal stability of group 2 sulphates increases down the group. Hence, $CaSO _4 < SrSO _4 < BaSO _4$.

Multiple choice chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids
Assertion (A): Group-$13$ doped crystals of silicon are called a p-type semiconductors.
Reason (R): Holes (positive in charge) appear to be responsible for the semiconducting properties.

  1. Both Assertion and Reason are true and Reason is the correct explanation of Assertion

  2. Both Assertion and Reason are true but Reason is not the correct explanation of Assertion

  3. Assertion is true but Reason is false.

  4. Assertion is false but Reason is true
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Doping silicon with Group 13 elements creates holes because there are fewer valence electrons than in silicon. These holes act as positive charge carriers, making it a p-type semiconductor.

Multiple choice chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

Which of the following statement is correct?

  1. Silicon doped with Boron is a n-type semi conductor.

  2. Silicon doped with Arsenic is a p-type semiconductor.

  3. Semiconductors are good conductors of electricity.

  4. Electrical conductivity of semiconductors increases with increasing temperature.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
The electrical conductivity of a semiconductor increases exponentially with an increase in temperature because as temperature is increased, more electrons get energy and can jump to the conduction band which increases conductivity.
$\sigma=Ce^{\displaystyle {-E _g} /{2KT}}$
Multiple choice chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

Assertion: Group-$15$ doped crystals of silicon are called an n-type semiconductor.


Reason: Neutrons are responsible for the semiconducting properties.

  1. Both Assertion and Reason are true and Reason is the correct explanation of Assertion

  2. Both Assertion and Reason are true but Reason is not the correct explanation of Assertion

  3. The Assertion is true but Reason is false

  4. The Assertion is false but Reason is true
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Group-15 doped crystals of silicon are called a n-type semiconductors because of the presence of a valence electron and electrons are responsible for the semiconducting properties.

Multiple choice chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

The density for simple cubic lattice is :


[where A is atomic weight, N is the Avogadro number and a is lattice parameter]

  1. $\displaystyle \frac{4A}{Na^3}$
  2. $\displaystyle \frac{2A}{Na^3}$
  3. $\displaystyle \frac{A}{Na^3}$
  4. $\displaystyle \frac{A}{Na^2}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Density = $\displaystyle \frac{\text{Mass of atom in unit cell}}{{\text{Total volume of unit cell}}} = \cfrac{nM}{V _cN _A} $


For simple cubic lattice, 

$n = 1  \\   V _c = a^3  \\$

$Given,  M = A$

$= \cfrac{A}{Na^3}$

Multiple choice chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids
Statement: The melting point of ice changes markedly with pressure.

State whether the given statement is true or false.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The melting point of ice is $0^oC$ $(32\ F,\ 273.15\ K)$ at standard pressure. A significant increase of pressure is required to lower the melting point of ordinary ice. The pressure exerted by an ice skater on the ice only reduces the melting point by approximately $0.09^oC$ $(0.16\ F)$.