81. Ferroelectric materials are the dielectrics and analogous to………materials.
(a) diamagnetic
(b) paramagnetic
(c) ferromagnetic
(d) antiferromagnetic
Answer: (c) ferromagnetic
82. Ferroelectrics are widely used as transducers.
(a) active
(b) passive
(c) electromechanical
(d) none of the above
Answer: (c) electromechanical
83. The materials having permanent electric moment are known as
(a) electrets.
(b) dielectrics.
(c) semiconductors.
(d) none of the above.
Answer: (a) electrets.
84. Consider the following statements: Electrets are the materials which are
- having permanent electric moments.
- electromagnets.
- very similar to permanent magnet materials.
- similar to anti-ferroelectric materials.
Which of the above statements is/are correct?
(a) 2 only.
(b) 1 and 3 only.
(c) 2 and 3 only.
(d) 1, 2, 3 and 4.
Answer: (c) 2 and 3 only.
85. Which one the following statements is correct?
(a) The absence of a hysteresis loop in a plot of polarization against field is proof of the absence of spontaneous polarization.
(b) The Curie temperature of a ferroelectric is the temperature above which its spontaneous polarization disappears.
(c) The Curie temperature of a ferroelectric is the temperature below which its spontaneous polarization disappears.
(d) Barium titanate is a ferroelectric because its lattice strains spontaneously above the Curie temperature.
Answer: (b) The Curie temperature of a ferroelectric is the temperature above which its spontaneous polarization disappears.
86. Magnetic material in VHF applications is
(a) silicon steel.
(b) Alnico.
(c) cobalt salt.
(d) ferrite.
Answer: (d) ferrite.
87. Air exhibits
(a) ferromagnetism.
(b) paramagnetism.
(c) anti-ferromagnetism.
(d) ferrimagnetism.
Answer: (b) paramagnetism.
88. Soft magnetic material is
(a) tungsten steel.
(b) Alcomax.
(c) bismuth.
(d) iron.
Answer: (d) iron.
89. Which one of the following materials can be used for permanent magnets?
(a) Alnico.
(b) Barium ferrite.
(c) Carbon steel.
(d) Iron-cobalt alloy.
Answer: (d) Iron-cobalt alloy.
90. Which one of the following is not a permanent magnetic material?
(a) Chromium steel.
(b) Silicon iron.
(c) Cobalt steel.
(d) Alnico.
Answer: (b) Silicon iron.
91. Which among the following magnetic materials has the highest energy-product to make it a permanent magnet?
(a) Alnico.
(b) Ferrite.
(c) Samarium cobalt.
(d) Cobalt-iron alloy.
Answer: (c) Samarium cobalt.
92. Which one of the following is correct? Ferrites are particularly suited for high frequency applications because of their
(a) low distortion.
(b) low eddy current loss.
(c) high conductivity.
(d) high mobility.
Answer: (b) low eddy current loss.
93. Up to about 4% silica is added in iron to be used as a soft magnetic material. The major reason for this is to
(a) increase permeability of the material.
(b) increase electrical resistivity of the material.
(c) increase the coercive force.
(d) increase the Saturation flux density.
Answer: (a) increase permeability of the material.
94. Soft iron is used in the manufacture of electromagnets because of its
(a) high saturation magnetization only.
(b) low retentivity only.
(c) low coercive field only.
(d) high saturation magnetization, low retentivity and low coercive field.
Answer: (c) low coercive field only.
95. Soft iron is used to manufacture electromagnets because it has
(a) high retentivity.
(b) high coercive field.
(c) low retentivity.
(d) low coercive field.
Answer: (d) low coercive field.
96. Magnetically hard materials do not possess which of the following characteristics?
(a) high retentivity.
(b) high coercivity.
(c) strong magnetic reluctance.
(d) zero differential permeability.
Answer: (c) strong magnetic reluctance.
97. Which one of the following classes of materials can be categorized as ferities?
(a) Plastics.
(b) Metals.
(c) Alloys.
(d) Ceramics.
Answer: (d) Ceramics.
98. High frequency transformer cores are generally made of
(a) cast iron.
(b) mu-metal.
(c) ferrite.
(d) graphite.
Answer: (c) ferrite.
99. A ferrite core has lower specific eddy current loss compared to an iron core because the ferrite core has
(a) higher electrical resistance.
(b) lower electrical resistance.
(c) higher permeability.
(d) lower permeability.
Answer: (a) higher electrical resistance.
100. A coil wound on a magnetic core is excited from an ac source. The source voltage and its frequency are both doubled. What will be the eddy current loss in the core?
(a) Four times the original value.
(b) Double the original value.
(c) Same as the original value.
(d) Half the original value.
Answer: (a) Four times the original value.