# Electronics and Communication Engineering - Materials and Components

### Exercise :: Materials and Components - Section 3

16.

The relaxation time of electrons in a metal is of the order of

 A. 10-6 secs B. 10-10 secs C. 10-14 secs D. 10-20 secs

Explanation:

No answer description available for this question. Let us discuss.

17.

Assertion (A): For elemental dielectrics, P = NaeEi where N is number of atoms/m3, P is polarization, ae is electronic polarization and Ei is internal electric field.

Reason (R): In elemental dielectrics there are no permanent dipoles or ions.

 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:

In elemental dielectrics Pi = Po = 0.

18.

The circumference of an electron orbit is equal to integer times the wavelength of electron.

 A. True B. False

Explanation:

No answer description available for this question. Let us discuss.

19.

In a specimen of silicon steel, a field strength of 200 A/m causes a flux density of 0.5 T. In a specimen of cast iron, the same H would cause B to be

 A. 0.5 T B. less than 0.5 T C. more than 0.5 T D. 0.5 T or more or less

Explanation:

Because cast iron has lower permeability than silicon steel.

20.

In a rare gas, the molecules of some atoms have an excess positive or negative charge. The electric field tends to shift positive ions relative to negative ions. This is known as ionic polarization.

 A. True B. False