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Materials and Components – Section 4(Page 3)

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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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