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Materials and Components – Section 2(Page3)

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Materials and Components – Section 2

21. In molecules of ionic crystals, orientation polarization is zero.
A. True
B. False

Answer: Option A
22. Assertion (A): CO2 has no resultant dipole moment but CO has a dipole moment.

Reason (R): The structure of CO2 is O = C = O.
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

Answer: Option A
23. 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
A. a change in o.c voltage
B. a change in s.c current
C. decrease in resistance
D. increase in resistance

Answer: Option C

Explanation:

It is the characteristic of a photoconductor that its resistance decreases with increase in illumination.
24. A permeable substance is one
A. which is strong magnet
B. which is a weak magnet
C. which is a good conductor
D. through which magnetic lines of force can pass easily

Answer: Option D
25. 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
A. ∈“r
B. both ∈‘r and ∈“r
C. ∈‘r
D. (∈“r)2

Answer: Option A

Explanation:

The imaginary part of ∈r gives rise to absorption of energy.
26. The classes of solid dielectrics are
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

Answer: Option C
27. A 200 turn coil has a self inductance of 10 mH. If the number of turns is doubled, all other quantities remaining the same, the self inductance will be
A. 2.5 mH
B. 5 mH
C. 20 mH
D. 40 mH

Answer: Option D

Explanation:

Inductance is proportional to square of number of turns.
28. A material which is lightly repelled by a magnetic field is known as
A. diamagnetic material
B. non-magnetic material
C. ferromagnetic material
D. paramagnetic material

Answer: Option A
29. Which of the following is the poorest conductor of electricity?
A. Aluminium
B. Nichrome
C. Copper
D. All of the above

Answer: Option B
30. The magnetic moment in units of Bohr magneton of a ferrous ion in any ferrite is
A. zero
B. 2
C. 4
D. 6

Answer: Option C

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