This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Ferroelectricity”.
1. Dielectrics which show spontaneous polarization are called as __________
Explanation: The Dielectric materials which exhibit spontaneous polarization, i.e., are polarized even in the absence of an applied electric field and whose polarization is reversible are called ferroelectric materials.
2. Polarization in Ferroelectric materials is ___________
Explanation: The polarization in the ferroelectric materials is reversible. Under suitable electric field, the polarization can be reversed as desired.
3. All ferroelectric materials are pyroelectric and piezoelectric.
Explanation: All the ferroelectric materials are pyroelectric and piezoelectric but the reverse is not true. Ferroelectricity can occur only in noncentrosymmetric crystals, just like piezoelectricity.
4. The temperature characteristic of every ferroelectric crystal is called ________
a) Transition Temperature
b) Crystal Temperature
c) Ferro Temperature
d) Weiss Temperature
Explanation: Every ferroelectric curve is characterized by a temperature called Ferroelectric curie temperature or transition temperature, above which it loses its ferroelectric behaviors and shows Para electric behavior.
5. The dielectric constant of a ferroelectric material changes with _______
c) Atmospheric Pressure
Explanation: The dielectric constant of a ferroelectric material changes with temperature according to the Curie-Weiss law which is given by: εr = B + C/T – Tc, where B and C are constants.
6. What happens in Ferroelectric material when T < Tc?
b) Spontaneously polarized
c) Becomes Para-electric
d) Hysteresis loss
Explanation: When the temperature is less than the transition temperature, the material becomes spontaneously polarized i.e., an electric polarization develops in it without the help of an externally applied field.
Explanation: The given graph shows the variation of dielectric constant with temperature T, for T > Tc. It is derived from the expression: εr = B + C/T – Tc, where B and C are constants.
8. The polarization left when the field is reduced to zero is called _______
a) Residual Polarization
b) Spontaneous Polarization
c) Permanent Polarization
d) Dipolar Polarization
Explanation: As we can see in a Hysteresis curve, as the field is lowered to zero, the left-over polarization is called the remnant/residual polarization.
Explanation: The A part in the figure is the region where spontaneous polarization takes place. As the field is lowered, the curve changes. This curve is known as hysteresis loop.
10. Which of the following is not a group of Ferroelectric Materials?
a) The Rochelle salt group
b) The KDP group
c) The Phosphate group
d) The Perovskites group
Explanation: The Ferroelectric materials are broadly classified into three major groups: The Rochelle salt group, the KDP group and the perovskites group headed by BaTiO3.
11. Rochelle salt is ferroelectric only in the Temperature range 255 K to 296 K.
Explanation: Rochelle salt has a unique property that is ferroelectric only in the temperature range of 255 K to 296 K. Other than this, the structure is orthorhombic while the structure is monoclinic in the ferroelectric phase.
12. The curie temperature for KH2PO4 is ________
a) 100 K
b) 123 K
c) 178 K
d) 273 K
Explanation: KH2PO4 is the most representative compound of the KPD group. They are characterized by the presence of hydrogen bonds in which the motion of the photon is related. The curie temperature is 123 K.
13. The symmetry of BaTiO3 in ferroelectric form is _________
c) Trigonal Bipyramidal
Explanation: In the ferroelectric form, BaTiO3 is tetragonal in shape as the crystal is slightly elongated owing to the polarization. In non-ferroelectric form, it is cubic.
Sanfoundry Global Education & Learning Series – Engineering Physics.
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