Materials and Components – Section 4(Page 3)

Materials and Components – Section 4

21. Semiconductors have a positive temperature coefficient of resistivity.
A.True
B.False

Answer: Option B

Explanation:

In semiconductors the temperature coefficient of resistivity is negative.

22. From a homogeneous and isotropic dielectric material of dielectric constant ∈r, a small volume element is taken out creating a cavity. The field can be kept homogeneous if Di. (i.e., electric flux density inside the cavity) and D0 (i.e., electric flux density outside the cavity) are such that
A.D0 = Di
B.
C.
D.either (a) or (b)

Answer: Option B

Explanation:

Since the field is homogeneous .

23. An electrolytic capacitor can be used for
A.ac only
B.dc only
C.both ac and dc
D.high frequency ac

Answer: Option B

24. Figure shows a composite capacitor. If CA, CB, CC are the capacitances of capacitors A, B, C, the overall capacitance C is
A.C = CA + CB + CC
B.C = (CA + CB) CC
C.C =
D.C =

Answer: Option C

Explanation:

B and C are in series and A is in parallel with this combination.

25. As regards ferromagnetic Curie temperature Qf and paramagnetic curie temperature θ
A.Qf > θ
B.θ > Qf
C.θ equal to or less than Qf
D.θ may be equal to less than or more Qf

Answer: Option B

26. If there are no permanent dipoles in a dielectric material, the dielectric constant is independent of temperature.
A.True
B.False

Answer: Option A

27. Assertion (A): Magnetic susceptibility of copper is -0.5 x 10-5.

Reason (R): Copper is diamagnetic material.

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

Explanation:

If magnetic susceptibility is very low μ, is nearly equal to 1 and the material is diamagnetic.

28. An electron shell corresponding to principal quantum number n can contain a maximum of
A.n2 electrons
B.2n2 electrons
C.2n electron
D.n3 electron

Answer: Option B

Explanation:

The electron shell corresponding to the principal quantum number can contain no more than 2n2 electrons.

29. A sheet of bakelite is inserted between the plates of an air capacitor. The capacitance will
A.increase
B.decrease
C.remain the same
D.may increase or decrease

Answer: Option A

Explanation:

Bakelite has higher permittivity than air.

30.The spin angular momentum along a given direction is either or .
A.True
B.False

Answer: Option A

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