Scroll to Top

# Materials and Components – Section 4

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

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)

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

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 =

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

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

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

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

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

Explanation:

Bakelite has higher permittivity than air.

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