# Materials and Components – Section 3(Page 3)

Materials and Components – Section 3

21.  The dielectric constant of ferroelectric materials can be expressed by the equation
 A.    B.    C.    D.    22.  A liquid has N permanent dipoles μp per unit volume and has been subjected to dc field for a long time such that orientation polarization is P0. At t = 0, the field is suddenly removed, then polarization
 A. will remain constant at P0 B. will become zero at t = 0 C. will delay to zero with a time constant D. either b or c

23. Assertion (A): Orbital magnetic moment of an electron in an atom is of the order of 1 Bohr magneton.

Reason (R): 1 Bohr magneton = 9.27 x 10-24 A/m2.

 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

24.  As per Bohr’s postulate, only those circular orbits are stable for which the angular momentum is equal to an integer times .
 A. True B. False

Explanation:

It is a quantum condition postulated by Bohr.

25.  Inductors used at V.H.F. are made using
 A. air core B. cast iron cored C. sheet steel cored D. thin film technique

Explanation:

Thin film technique ensure low hysteresis and eddy current losses.

26.  If a capacitor C having selectivity factor Q is scaled down in all its dimensions by a factor K without any altering the dielectric material, the new capacitor will have capacitance and selectivity as
 A. C,    B.    , Q C.    ,    D. C, K

Explanation:

Since the dimension of plates is scaled down by K, the area decreases by a factor of K2, the distance between plates decreases by a factor of K.

Therefore, capacitance changes to .

The selectivity will not be affected.

27.  The hysteresis loss is
 A. proportional to frequency B. independent of frequency C. proportional to (frequency)2 D. proportional to    28.  If m, v, r are the mass, velocity and radius of orbit of electron and h is Planck’s constant, quantum condition for electron’s orbit is
 A.    B.    C.    D.    Explanation:

For stable circular orbit angular momentum is equal to integer times .

29. Assertion (A): For a magnetic material M = (μr – 1) H, where M is magnetic dipole moment/m3, H is field intensity A/m and μr is relative permeability.

Reason (R): μr can have any value from 0 to hundreds of thousands.

 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:

μr is always more than 1. It cannot be 0 or less than 1.

30.  As regards ∈0 and ∈r (absolute and relative permittivity)
 A. both ∈0 and ∈r can be interpreted in terms of atomic properties of medium B. only ∈r can be interpreted in terms of atomic properties of medium C. only ∈0 can be interpreted in terms of atomic properties D. ∈r has no physical significance