Materials and Components problems
- 1. When subjected to alternating stresses, an insulating material is characterised by complex dielectric constant ?'r - j?"r . In such materials, the dielectric losses under alternating stress is proportional
Options- A. ?"r
- B. both ?'r and ?"r
- C. ?'r
- D. (?"r)2 Discuss
Correct Answer: ?"r
Explanation:
The imaginary part of ?r gives rise to absorption of energy.
- 2. Assertion (A): Relaxation time and mean time between collisions are equal when scattering is isotropic.
Reason (R): Mean free path of an electron ?, velocity of electron v and mean time between collisions tc are related as ? = vTc.
Options- A. Both A and R are true and R is correct explanation of A
- B. Both A and R are true but R is not correct explanation of A
- C. A is true but R is false
- D. A is false but R is true Discuss
Correct Answer: Both A and R are true but R is not correct explanation of A
- 3. Assertion (A): CO2 has no resultant dipole moment but CO has a dipole moment.
Reason (R): The structure of CO2 is O = C = O.
Options- A. Both A and R are true and R is correct explanation of A
- B. Both A and R are true but R is not correct explanation of A
- C. A is true but R is false
- D. A is false but R is true Discuss
Correct Answer: Both A and R are true and R is correct explanation of A
- 4. Paramagnetic materials have permanent magnetic dipoles but interaction between neighbouring dipoles is negligible.
Options- A. True
- B. False Discuss
Correct Answer: True
- 5. Assertion (A): Copper is a monoatomic solid.
Reason (R): In a metal the valence electrons belong to all atoms.
Options- A. Both A and R are true and R is correct explanation of A
- B. Both A and R are true but R is not correct explanation of A
- C. A is true but R is false
- D. A is false but R is true Discuss
Correct Answer: Both A and R are true but R is not correct explanation of A
- 6. If q is charge on an electron, R is radius of electron orbit and ? is angular velocity of electron rotation, the magnetic dipole moment of electron in orbit is
Options- A. 0.5 q?R
- B. 0.5 q2?2R2
- C. 0.5 q?R2
- D. 0.5 q?2R Discuss
Correct Answer: 0.5 q?R2
- 7. The classes of solid dielectrics are
Options- A. A, B, C, D, E, F, H
- B. A E B F H C D
- C. Y A E B F H C
- D. A E B F H C Discuss
Correct Answer: Y A E B F H C
- 8. For a photoconductor with equal electron and hole mobilities and perfect ohmic contacts at the ends, an increase in intensity of optical illumination results in
Options- A. a change in o.c voltage
- B. a change in s.c current
- C. decrease in resistance
- D. increase in resistance Discuss
Correct Answer: decrease in resistance
Explanation:
It is the characteristic of a photoconductor that its resistance decreases with increase in illumination.
- 9. Assertion (A): If WF is Fermi energy, v is velocity of electron and m is mass of electron, then
.Reason (R): Conductivity of a metal depends on temperature and impurity concentration.
Options- A. Both A and R are true and R is correct explanation of A
- B. Both A and R are true but R is not correct explanation of A
- C. A is true but R is false
- D. A is false but R is true Discuss
Correct Answer: Both A and R are true but R is not correct explanation of A
- 10. The temperature below which certain materials are antiferromagnetic and above which they are paramagnetic is called
Options- A. Weiss temperature
- B. Curie temperature
- C. Neel temperature
- D. None of the above Discuss
Correct Answer: Neel temperature
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