materials and components section 2

8/18/2019 Materials and Components Section 2

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ELECTRONICS AND COMMUNICATIONS ENGINEERING: MATERIALS AND COMPONENTS sec. 2

1. In crystalline solids, atoms are stacked in a regular manner.

A.True

B. False

2. The temperature below which certain materials are antiferromagnetic and above which they areparamagnetic is called

A. Weiss temperature

B. urie temperature

C.!eel temperature

D. !one of the above

". In metals, the average drift velocity of electron per unit field is called mobility.

A.True

B. False

#. Ferrites have

A. a low copper loss

B.low eddy current loss

C. low resistivity

D. higher specific gravity compared to iron

$esistivity of ferrites is very high as compared to that of iron. %ence eddy curretns are muchless.

&. In intrinsic semiconductors, the number of free electrons is e'ual to the number of mobile holes.

A.True

B. False

When a material becomes a superconductor, its resistivity becomes

A. very small


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B.(ero

C. about 1)* of normal value

D. about 2)* of normal value + superconductor has (ero resistance.

. In a pie(oelectric crystal, the application of mechanical force will cause

A. plastic deformation of crystal

B.magnetic dipoles in the crystal

C. electrical polari(ation in the crystal

D. shift in Fermi level

-ie(oelectric materials permit conversion of mechanical force into electrical energy.

. onsider the following statementIf an electric field is applied to an n type semiconductor bar, the electrons and holes move inopposite directions due to their opposite charges. The net currents is

1. both due to electrons and holes with electrons as ma/ority carriers

2. sum of hole and electron currents

". difference between electron and hole currents.

Which of above statements are correct0

A. 1 only

B.1 and 2

C. 2 only

D. " only

The net current is sum of currents due to holes and electrons.

In n type materials, electrons are ma/ority carriers.

. +s the temperature of a pure silicon specimen is increased


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A. the number of free electrons increases

B. the number of holes decreases

C. the number of holes increases

D.the number of free electrons and holes increases

1). +ssertion +34 In many materials, dielectric polari(ation causes mechanical distortion.

$eason $34 If dielectric polari(ation causes mechanical distortion then mechanical distortion mustcause dielectric polari(ation.

A. 5oth + and $ are true and $ is correct e6planation of +

B. 5oth + and $ are true but $ is not correct e6planation of +

C.+ is true but $ is false

D. + is false but $ is true

11.7emi conducting materials are all

A. elements

B. compounds

C.elements or compounds

D. elements or mi6tures

8any compounds also show semiconducting properties.

12. 7ilicon and germanium atoms combine orderly into array of atoms located in repetitivegeometric pattern. This pattern is called

A.crystal

B. covalent bond


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C. molecule

D. valence bond

1". In a pure sample of silicon

A.the number of holes and free electrons is always e'ual

B. the number of free electrons is more than the number of holes

C. the number of free electrons and holes is e'ual at low temperature

D. the number of free electrons is less than number of holes

1# 9rbital magnetic dipole moment is due to the motion of electron in its orbit around nucleus.

A.True

B. False

1&. +ssertion +34 ∈ r can be determined e6perimentally by measuring the capacitance of a parallelplate capacitor with and without the dielectric.

$eason $34 apacitance of a parallel plate capacitor : .

A.5oth + and $ are true and $ is correct e6planation of +


C. + is true but $ is false


1;. In a homogeneous magnetic field % of a solenoid, the core carries a magnetic dipole moment 8per unit volume e'ual to

A. < ) %


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B. < r %

C.


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Reason (R): Thermionic emission current ∝ T 2 e =CwDk T.





21. In molecules of ionic crystals, orientation polari(ation is (ero.

A.True

B. False

22. Assertion (A): 9 2 has no resultant dipole moment but 9 has a dipole moment.

Reason (R): The structure of 9 2 is 9 : : 9.





2". For a photoconductor with e'ual electron and hole mobilities and perfect ohmic contacts at theends, an increase in intensity of optical illumination results in

A. a change in o.c voltage

B. a change in s.c current

C. decrease in resistance

D. increase in resistance

It is the characteristic of a photoconductor that its resistance decreases with increase inillumination.

2#. + permeable substance is one


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A. which is strong magnet

B. which is a weak magnet

C. which is a good conductor

D.through which magnetic lines of force can pass easily

2&. When sub/ected to alternating stresses, an insulating material is characterised by comple6dielectric constant ∈ ' r = j ∈ " r . In such materials, the dielectric losses under alternating stress isproportional

A. ∈ " r

B. both ∈ ' r and ∈ " r

C. ∈ ' r

D. ∈ " r 32

The imaginary part of ∈ r gives rise to absorption of energy.

2;. The classes of solid dielectrics are

A. +, 5, , E, C, F, %

B. + C 5 F % E

C. + C 5 F %

D. + C 5 F %

2 .+ 2)) turn coil has a self inductance of 1) m%. If the number of turns is doubled, all other'uantities remaining the same, the self inductance will be

A. 2.& m%

B. & m%


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C. 2) m%

D.#) m%

Inductance is proportional to s'uare of number of turns.

2 . + material which is lightly repelled by a magnetic field is known as

A.diamagnetic material

B. non=magnetic material

C. ferromagnetic material

D. paramagnetic material

2 . Which of the following is the poorest conductor of electricity0

A. +luminium

B.!ichrome

C. opper

D. +ll of the above

"). The magnetic moment in units of 5ohr magneton of a ferrous ion in any ferrite is

A. (ero B. 2

C.#

D. ;

"1. The relationship of hysteresis loss to ma6imum flu6 density was first determined by

A.. 7teinmet(

B. G.$. Birchoff

C. 8r. Haplace


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D. 8r. +mpere

"2. In metals the thermal conductivity K and electrical conductivity are related as BD T3 : H, H isknown as

A. Hattice constant

B.Horent( number

C. Hanevin function

D. Harmor number

"". Assertion (A): If W F is Fermi energy, v is velocity of electron and m is mass of electron,

then .

Reason (R): onductivity of a metal depends on temperature and impurity concentration.


B.5oth + and $ are true but $ is not correct e6planation of +



"#. Eielectric constant of transformer oil is about

A. 1 B.#

C. 1) D. 2)

"&. Assertion (A): When an electron is revolving in its orbit and magnetic field is also present, theangular fre'uency of electron will be affected by the magnetic field.

Reason (R): In the case of electron revolving in its orbit in the presence of magnetic field, theorbital magnetic dipole moment is not affected by the presence of magnetic field.


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C.

+ is true but $ is false


9rbital magnetic moment is e'ual to = e D2m 3.

";. In carbon resistor colour code, the third band is red. It indicates

A.two (eros

B. three (eros

C. multiplier is ).)1

D. multiplier is ).1

" . $ochelle salt is a ferroelectric material.

A.True

B. False

" . -aramagnetic materials have permanent magnetic dipoles but interaction between neighbouringdipoles is negligible.

A.True

B. False

" . Assertion (A): If difference between static and optical dielectric constant is high, the mechanicalcompressiblity of that material is also high.

Reason (R): For soft ions, ionic polari(ation per unit field is higher than that of hard ions.





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#). Assertion (A): In Figure, the intercept of the line on y =a6is is e'ual to N α e J α i 3, where N is

number of atomsDm " , α e is electronic polari(ability and α i is ionic polari(ability.

Reason (R): α e and α i are independent of temperature.





The intercept on y =a6is e'uals ! α e J α i 3.

This intercept is constant because α e and α i are independent of temperature.

#1. Assertion (A): The optical dielectric constant i.e., K r at optical fre'uencies3of ionic dielectrics isless than static dielectric constant.

Reason (R): +t optical fre'uencies, - i : ).






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#2. + piece of iron is placed in a magnetic field

A. the magnetic field will not be affected

B.the magnetic lines of force will bend to pass through the piece

C. the magnetic lines of force will bend away from the piece

D. any of the above depending on type of iron

#". Assertion (A): 8agnetism can be e6plained by the theory of magnetic domains.

Reason (R): The e6istence of magnetic domains is evident from the 5itter powder patterns.





##. Ferromagnetic materials

A. shows spontaneous magnetisation below a certain temperature

B. have resistivity very high as compared to that of iron

C. can be used even at microwave fre'uencies

D.all of the above

#&. In a specimen of ferromagnetic material, as the flu6 density is increased from (ero to 2.& T, L r will

A. increase

B. decrease

C. first decrease then increase


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D.first increase then decrease

#;. Assertion (A): $ela6ation time and mean time between collisions are e'ual when scattering isisotropic.

Reason (R): 8ean free path of an electron M, velocity of electron v and mean time betweencollisions τ c are related as M : v Tc .





# . Assertion (A): opper is a monoatomic solid.

Reason (R): In a metal the valence electrons belong to all atoms.





# . The heat developed per m " per second W3 in a conductor having a conductivity and a field C is

A.W : C 2

B. W : C

C.W :

D. W : C3 ).&

# . The number of valence electrons in acceptor impurity are


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A. & B. #

C."

D. 1

&). If q is charge on an electron, $ is radius of electron orbit and ? is angular velocity of electronrotation, the magnetic dipole moment of electron in orbit is

A. ).& q ?$

B. ).& q 2? 2$ 2

C.).& q ?$ 2

D. ).& q ? 2$

materials and components section 2

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