Tag: electrical and magnetic properties of solids

Questions Related to electrical and magnetic properties of solids

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

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

  1. p-type

  2. n-type

  3. Both A and B

  4. None of the the above

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Correct Option: B
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.

Select the correct statement.

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

  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

Show answer
Correct Option: C
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, $CaSO _4 < SrSO _4 < BaSO _4$.

A semiconductor of Ge can be made p-type by adding which impurity?

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

  1. trivalent impurity

  2. tetravalent impurity

  3. pentavalent impurity

  4. hexavalent impurity

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Correct Option: A
Explanation:

A semiconductor of Ge can be made p-type by adding trivalent impurity and for n-type SC pentavalent impurity is dopped.

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.
chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  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

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Correct Option: A

Which of the following statement is correct?

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

  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.

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Correct Option: D
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.
$\sigma=Ce^{\displaystyle {-E _g} /{2KT}}$

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


Reason: Neutrons are responsible for the semiconducting properties.

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

  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

Show answer
Correct Option: C
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.

The density for simple cubic lattice is :


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

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

  1. $\displaystyle \frac{4A}{Na^3}$

  2. $\displaystyle \frac{2A}{Na^3}$

  3. $\displaystyle \frac{A}{Na^3}$

  4. $\displaystyle \frac{A}{Na^2}$

Show answer
Correct Option: C
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, 

$n = 1  \\   V _c = a^3  \\$

$Given,  M = A$

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

Statement: The melting point of ice changes markedly with pressure.

State whether the given statement is true or false.
chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. True

  2. False

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Correct Option: A
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 $0.09^oC$ $(0.16\ F)$.

Glass is an example of _____ solids.

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

  1. amorphous

  2. shaped

  3. structured 

  4. determinate

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Correct Option: A
Explanation:

Glass is a non-crystalline, often transparent amorphous solid, that has widespread practical, technological, and decorative uses in, for example, window panes, tableware, optics, and optoelectronics.


Hence, the correct option is $\text{A}$

Statement: In an insulator, the band gap is small.

State whether the given statement is true or false.
chemistry solid state electrical and magnetic properties of solids impurity defects properties of solids

  1. True

  2. False

Show answer
Correct Option: B
Explanation:

In an insulator, the bandgap is large. More energy is required to promote electrons from valence band to conduction band. This energy is not available. The electrons remain in the valence band and cannot move freely. Hence, insulators are bad conductors of heat and electricity.


Hence, the given statement is $\text{false}$