32
MCQ (Single Correct Answer)
A ferromagnetic substance becomes a permanent magnet when it is placed in a magnetic field because .......... .
A
all the domains get oriented in the direction of magnetic field
B
all the domains get oriented in the direction opposite to the direction of magnetic field
C
domains get oriented randomly
D
domains are not affected by magnetic field
33
MCQ (Single Correct Answer)
The correct order of the packing efficiency in different types of unit cells is ............ .
A
fcc $<$ bcc $<$ simple cubic
B
fcc $>$ bcc $>$ simple cubic
C
fcc $<$ bcc $>$ simple cubic
D
$\mathrm{bcc}<\mathrm{fcc}>$ simple cubic
34
MCQ (Single Correct Answer)
Which of the following defects is also known as dislocation defect?
A
Frenkel defect
B
Schottky defect
C
Non-stoichiometric defect
D
Simple interstitial defect
35
MCQ (Single Correct Answer)
In the cubic close packing, the unit cell has ............. .
A
4 tetrahedral voids each of which is shared by four adjacent unit cells
B
4 tetrahedral voids within the unit cell
C
8 tetrahedral voids each of which is shared by four adjacent unit cells
D
8 tetrahedral voids within the unit cells
36
MCQ (Single Correct Answer)
The edge lengths of the unit cells in terms of the radius of spheres constituting fcc, bcc and simple cubic unit cells are respectively ............. .
A
$2 \sqrt{2 r}, \frac{4 r}{\sqrt{3}}, 2 r$
B
$\frac{4 r}{\sqrt{3}}, 2 \sqrt{2 r}, 2 r$
C
$2 r, 2 \sqrt{2 r}, \frac{4 r}{\sqrt{3}}$
D
$2 r, \frac{4 r}{\sqrt{3}}, 2 \sqrt{2 r}$