(d) A is false but R is true
1. (A): At absolute zero degrees Kelvin temperature the semiconductor materials behave as insulators
(R): At absolute zero degrees Kelvin temperature, there is no energy available to generate the current carriers in the semiconductor.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. a[/otw_shortcode_content_toggle]
2. (A): Electron mobility in metals decreases with increasing temperature.
(R): In metals electron concentration is high.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. b[/otw_shortcode_content_toggle]
3. (A): A heavily doped semiconductor can exhibit positive temperature coefficient of resistance.
(R): The carrier mobility decreases with an increase of temperature.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. a[/otw_shortcode_content_toggle]
4. (A): An electric or mechanical input makes the flux jump from one superconductor to another, generating large direct current.
(R): The electric resistivity of superconductors depends upon the magnetic field.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. d[/otw_shortcode_content_toggle]
5. (A): A superconductor is a perfect diamagnetic material.
(R): A superconductor is a perfect conductor.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. c[/otw_shortcode_content_toggle]
6. (A): Superconductors cannot be used as coils for production of strong magnetic fields.
(R): Superconductivity in a wire may be destroyed if the current in the wire exceeds a critical value.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. a[/otw_shortcode_content_toggle]
7. (A): Superconductivity of a superconducting material can be destroyed by application of an external magnetic field.
(R): if the applied magnetic field is greater than the critical magnetic field at a given temperature which is more than the transition temperature, superconductivity can be destroyed.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. c[/otw_shortcode_content_toggle]
8. (A): Cryotron is a switch constructed out of superconducting materials.
(R): Switching action is characteristic of superconductors only.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. c[/otw_shortcode_content_toggle]
9. (A): if a piece of metal is made to have a temperature gradient between its two ends, an emf exist between these ends.
(R): Electrons at the hot end move towards the cold end.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. a[/otw_shortcode_content_toggle]
10. (A): Thermal noise in metallic resistors can be characterized by Gaussian probability density function.
(R): Power spectral density of thermal noise is essentially constant for a very large frequency range.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. b[/otw_shortcode_content_toggle]
11. (A): Ammonium dihydrogen phosphate is a piezoelectric material.
(R): There is no centre of symmetry in ammonium dihydrogen phosphate.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. a[/otw_shortcode_content_toggle]
12. (A): The Diamagnetic effect is present in all the materials.
(R): The applied magnetic field alters the orbital motion of the constituent electrons of the material.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. d[/otw_shortcode_content_toggle]
13. (A): The spins within a magnetic domain are aligned permanently below Curie temperature in a ferromagnetic material.
(R): Ferromagnetic material is magnetic only when the domains are aligned by an external field.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. c[/otw_shortcode_content_toggle]
14. (A): Iron, cobalt and nickel are ferromagnetic.
(R): Spin imbalance of electrons in the 3rd band is responsible.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. a[/otw_shortcode_content_toggle]
15. (A): Soft magnetic material is used in making electromagnets.
(R): Soft magnetic materials have a high coercive field.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. c[/otw_shortcode_content_toggle]
16. (A): Soft magnetic materials cannot be used for the construction of cores for the electrical machines.
(R): Soft magnetic materials have relatively small and narrow hysteresis loop.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. d[/otw_shortcode_content_toggle]
17. (A): Alnico (aluminium-nickel-iron-cobalt) alloys are the mass importation of hard magnetic materials.
(R): Alnico magnet alloys have the lowest energy per unit of volume of any permanent magnet material available commercially.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. c[/otw_shortcode_content_toggle]
18. (A): Hard magnetic materials are used for making permanent magnets.
(R): Hard magnetic materials have relatively small and narrow hysteresis loop.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. c[/otw_shortcode_content_toggle]
19. (A): DC resistance of ferrites is much higher than that of dia-, para- or ferromagnetic materials.
(R): Ferrites are obtained by replacing divalent ferrous ion in ferrimagnetic magnetite by another divalent metal such as Mg, Zn etc., but the exchange interactions are the antiferromagnetic type.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. b[/otw_shortcode_content_toggle]
20. (A): Ferrites are useful at very high frequencies.
(R): Ferrites have high permeability and high resistivity.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. a[/otw_shortcode_content_toggle]
21. (A): Ferrites cores are used in inductances for high frequencies.
(R): Ferrites provide high flux density with minimum eddy current loss and are insulators.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. a[/otw_shortcode_content_toggle]
22. (A): Magnetic cores are generally used in main memory of a digital computer.
(R): Magnetic cores are slow and volatile.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. c[/otw_shortcode_content_toggle]
23. (A): Storage of energy in a dielectric is due to shift in relative positions of internal charges against normal atomic and molecular forces.
(R): All dielectrics are characterised by the presence of molecules having a permanent displacement between the centres of gravity of the positive and negative charges.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. a[/otw_shortcode_content_toggle]
24. (A): An insulator has a high value of resistivity, and with increasing temperature, the value of its resistivity decreases exponentially.
(R): With increasing temperature, the value of the energy band gap decreases.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. d[/otw_shortcode_content_toggle]
25. (A): The relative dielectric constant of an insulator decreases with increase in the frequency of the applied alternating field.
(R): With an increase in the frequency of the applied field, the polarization process increases in number.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. c[/otw_shortcode_content_toggle]
26. (A): Mica is usually not used for slot linings of high voltage machines.
(R): Space factor in high voltage machines is high.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. c[/otw_shortcode_content_toggle]
27. (A): Skin depth is the depth by which electromagnetic wave has been increased to 37% of its original value.
(R): The depth of penetration of wave in a lossy dielectric increase with increasing wavelength.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. c[/otw_shortcode_content_toggle]
28. (A): Sulphur hexafluoride gas is highly inflammable.
(R): Sulphur hexafluoride gas is used in switchgear.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. d[/otw_shortcode_content_toggle]
29. (A): Mica has very high dielectric strength.
(R): Mica cannot be used for the large commutator of a dc machine.
[otw_shortcode_content_toggle title=”Show Answer” opened=”closed” icon_type=”general foundicon-checkmark”]Answer. b[/otw_shortcode_content_toggle]
Thanks sir. Its useful for ies preparation.