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Materials and Components – Section 3(Page 2)

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Materials and Components – Section 3

11. The resistivity of intrinsic semiconductors, at room temperature, is of the order of
A. 1 Ω-m
B. 1000 Ω-m
C. 106 Ω-m
D. 10-3 Ω-m

Answer: Option A
12. Assertion (A): Ferromagnetic materials possess ferromagnetic properties only when temperature is less than paramagnetic curie temperature.

Reason (R): For a ferromagnetic material

for T > θf.
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
13.  In terms of classical representation of electrons
A. an atom is essentially empty
B. an atom is essentially full
C. an atom may be essentially empty or full depending on the material
D. an atom may be essentially empty or full depending on temperature

Answer: Option A
14.  To produce magnetic flux, mmf is necessary.
A. True
B. False

Answer: Option A

 

15.  For a polyatomic gas, the equation relating dielectric constant ∈r with molecular properties is
A.
B.
C.
D.

Answer: Option A
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

Answer: Option C
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

Answer: Option A

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

Answer: Option A
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

Answer: Option B
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

Answer: Option A

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