Solid State Test

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Solid State Test - 14

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Weekly Quiz Competition

Question 1
1 / -0

Which of the following is true about the charge acquired by p-type semiconductors?

A
Positive

B
Neutral

C
Negative

D
Depends on concentration of p impurity

Solution

p-type semiconductor by itself has mainly positively charged carriers (holes) which are able to move freely .It is , however , still neutral because the fixed acceptor atoms having accepted electrons are negative.
Question 2
1 / -0

To get a n-type semiconductor from silicon, it should be doped with a substance with valence ................

A
2

B
1

C
3

D
5

Solution

When silicon is doped with a pentavalent substance like P or As , four out of five electrons are used in the formation of four covalent bonds with four of its neighbouring silicon atoms.The fifth electron is extra and becomes delocalised. These delocalised electrons increase the conductivityy of doped silicon.
Question 3
1 / -0

The total number of tetrahedral voids in the face centred unit cell is .................

A
6

B
8

C
10

D
12

Solution

In face centred unit cell the number of atoms per unit cell = 4 atoms therefore , the number of tetrahedral voids in fcc unit cell = 8
Question 4
1 / -0

Which of the following point defects are shown by AgBr(s) crystals?

(A) Schottky defect

(B) Frenkel defect

(C) Metal excess defect

(D) Metal deficiency defect

A
(A) and (B)

B
(C) and (D)

C
(A) and (C)

D
(B) and (D)

Solution

AgBr shows both Frenkel as well as Schottky deffects.
Question 5
1 / -0

In which pair most efficient packing is present?

A
hcp and bcc

B
hcp and ccp

C
bcc and ccp

D
bcc and simple cubic cell

Solution

In hcp and ccp the packing efficiency is maximum ( ie. 74% ) , hence this pair of packing is considered as " most efficient packing".
Question 6
1 / -0

The percentage of empty space in a body centred cubic arrangement is ...............

A
74

B
68

C
32

D
26

Solution

Since the packing efficiency in bcc arrangement is 68% , therefore the percentage empty space = (100 - 68) = 32
Question 7
1 / -0

Which of the following statement is not true about the hexagonal close packing?

A
The coordination number is 12.

B
It has 74% packing efficiency

C
Tetrahedral voids of the second layer are covered by the spheres of the third layer.

D
In this arrangement spheres of the fourth layer are exactly aligned with those of the first layer.

Solution

In hexagonal close packed structure there is ABAB.......type pattern. This means that in this case spheres of third layer are exactly aligned with those of the first layer.. Thus the pattern of spheres is repeated in alternate layers. Thus the statement at (iv) is not true about hexagonal closed packing.
Question 8
1 / -0

Which of the following statements are true about semiconductors?

(i) Silicon doped with electron rich impurity is a p-type semiconductor.

(ii) Silicon doped with an electron rich impurity is an n-type semiconductor.

(iii) Delocalised electrons increase the conductivity of doped silicon.

(iv) An electron vacancy increases the conductivity of n-type semiconductor.

A
(ii) and (iii)

B
(i) and (ii)

C
(i) and (iv)

D
(iv) and (iii)

Solution

Silicon (valence electron – 4) doped with electron rich impurity is an n-type semiconductor due to extra electron and the delocalised electrons increase the conductivity of doped silicon.
Question 9
1 / -0

An excess of potassium ions makes KCl crystals appear violet or lilac in colour since .....

(i) some of the anionic sites are occupied by an unpaired electron.

(ii) some of the anionic sites are occupied by a pair of electrons

(iii) there are vacancies at some anionic sites.

(iv) F-centres are created which impart colour to the crystals.

A
(i), (iv)

B
(i), (ii)

C
(iii), (iv)

D
(ii), (iv)

Solution

An excess of potassium ions makes KCl crystals appear violet due to' nonstoichiometric - metal excess defect' . The anionic vacancies are caused due to movement of potassium atoms to the surface of the crystal when KCl is heated in an atmosphere of potassium vapours.The \(Cl^-\) ions then diffuse to the surface .This happens by loss of electron by potassium atom to form \(K^+\) ions. The released electrons diffuse into the crystal and occupy anionic sites. The anionic sites occupied by unpaired electrons are called F-centres. The Fcentres impart colour to the crystals (e.g. yellow to NaCl and violet to KCl) due to excitation of these electrons by absorbing energy from the visible light falling on the crystals.
Question 10
1 / -0

The number of tetrahedral voids per unit cell in NaCl crystal is ........

(i) 4

(ii) 8

(iii) twice the number of octahedral voids.

(iv) four times the number of octahedral voids.

A
(ii) and (iii)

B
(i) and (ii)

C
(iv) and (i)

D
(i) and (iii)

Solution

The number of tetrahedral voids per unit cell in NaCl is calculated as

Since NaCl has fcc lattice.

No. of atoms (n) per unit cell = 4

No. of octahedral void = n = 4

No. of tetrahedral void \(= 2n = 2\times 4 = 8\)

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Solid State Test - 14

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Solid State Test - 14

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SHARING IS CARING

Question 1

Positive

Neutral

Negative

Depends on concentration of p impurity

Solution

Question 2

2

1

3

5

Solution

Question 3

6

8

10

12

Solution

Question 4

(A) and (B)

(C) and (D)

(A) and (C)

(B) and (D)

Solution

Question 5

hcp and bcc

hcp and ccp

bcc and ccp

bcc and simple cubic cell

Solution

Question 6

74

68

32

26

Solution

Question 7

The coordination number is 12.

It has 74% packing efficiency

Tetrahedral voids of the second layer are covered by the spheres of the third layer.

In this arrangement spheres of the fourth layer are exactly aligned with those of the first layer.

Solution

Question 8

(ii) and (iii)

(i) and (ii)

(i) and (iv)

(iv) and (iii)

Solution

Question 9

(i), (iv)

(i), (ii)

(iii), (iv)

(ii), (iv)

Solution

Question 10

(ii) and (iii)

(i) and (ii)

(iv) and (i)

(i) and (iii)

Solution

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