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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