materials and components section 1

8/18/2019 Materials and Components Section 1

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ELECTRONICS AND COMMUNICATIONS ENGINEERING:MATERIALS AND COMPONENTS sec. 1

1.

Diamond is a paramagnetic material.

A. True

B.False

Diamond is diamagnetic.

2.

Which capacitor-store higher amount of energy?

A. Air capacitor

B. Paper capacitor

C. Mica capacitor

D. Plastic film capacitor

Energy stored is proportional to capacitance and capacitance is proportional to permittivity.

3.

Above ferroelectric curie temperature, spontaneous polarization in ferroelectric materials becomes

stronger.

A. True

B. False

Spontaneous polarization vanishes above ferro-electric Curie temperature.

4.

In paramagnetic materials

A.permanent magnetic dipoles exist but the interaction between neighbouring dipoles is

negligible


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B. permanent magnetic dipole do not exist

C.permanent magnetic dipoles exist and the interaction between neighbouring dipoles is very

strong

D. permanent magnetic dipole moment may or may not exist

In paramagnetic materials interaction between neighbouring dipoles is negligible.

5.

Assertion (A): Atomic number of sodium is 11.

Reason (R): Sodium has a body centred cubic lattice.

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

Atomic number is not dependent on lattice structure.

6.

The conductivity of intrinsic semiconductor is given by

A. eni(μ p - μn)

B. eni(μ p + μn)

C. ni(μ p + μn)

D. ni(μ pμn)

For intrinsic semiconductor,

Conductivity = (Electron charge) x (Number of charge carriers) x (Sum of mobilities of holes and

electrons).


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7.

The core of a coil has a length of 10 cm. The self inductance is 8 mH. If the core length is doubled, all

other quantities remaining the same, the self inductance will be

A. 32 mH

B. 16 mH

C. 8 mH

D. 4 mH

Inductance is inversely proportional to the core length.

8.

The minority carrier life time and diffusion constant in a semiconducting material are 100 μs and 100

cm2 /s respectively. The diffusion length of carriers is

A. 0.1 cm

B. 0.01 cm

C. 0.0141 cm

D. 1 cm

Diffusion length = sqrt(Carrier life time x Diffusion constant) = (100 x 10-6 x 100)

0.5 = 0.1 cm.

9.

Assertion (A): Electronic and Ionic polarization in a polyatomic gas are independent of temperature.

Reason (R): The orientation polarization is independent of temperature.

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


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D. A is false but R is true

Orientation polarization is inversely proportional to temperature.

10.

Two materials having temperature coefficients of 0.004 and 0.0004 respectively are joined in series.

The overall temperature coefficient is likely to be

A. 0.08 B. 0.04

C. 0.001 D. 0.0001

The overall temperature coefficient will be less than 0.004 and more than 0.0004.

11.

The number of valence electrons in pentavalent impurity is

A. 5 B. 4

C. 3 D. 1

Pentavalent means 5 valence electrons.

12.

If the diameter of a wire is doubled, its current carryin capacity becomes

A. one!fourth

B. half

C. twice

D. four times

"urrent carryin capacity depends on area of cross!section.


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13.

The law # $ %&, where # is current density, % is electrical conductivity and & is field strenth is

A. 'hm(s law

B. )auss law

C. *mpere(s law

D. +iot!avart law

It is another form of 'hm(s law.

14.

Assertion (A): ilicon is less sensitive to chanes in temperature than ermanium.

Reason (R): "ut in voltae in silicon is less than that in ermanium.

A. +oth * and - are true and - is correct eplanation of *

B. +oth * and - are true but - is not correct eplanation of *


D. * is false but - is true

"ut in voltae of silicon is hiher than that in ermanium.

15.

/aterial which lac0 permanent manetic dipoles are 0nown as

A. paramanetic B. diamanetic

C. ferromanetic D. ferrimanetic

iamanetic materials have no permanent manetic diploes.

1. * parallel plate capacitor has its lenth, width and separation doubled. It frinin effects are

nelected, to 0eep the capacitance same, the dielectric constant must be

A.halved


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B. 0ept the same

C. doubled

D. made 4 times

. hen dimensions are chaned, * become four times and d becomes twice.

ince ∈ is constant, ∈r must be halved to 0eep " constant.

1. Assertion (A): In imperfect capacitors, the current does not lead the applied ac voltae by 67.

Reason (R): hen sub8ected to ac fields, the dielectric constant can be epressed as ∈' r ! j ∈" r .

A.+oth * and - are true and - is correct eplanation of *


C. * is true but - is false


Imainary part of ∈r ives rise to absorption of enery by the material from alternatin field.

9ence current does not lead the voltae by 67.

1:. In atomic physics, a state with l $ is called p state.

A. True B. False

The state with l $ is called s state.

16. If a sample of ermanium and a sample of silicon have the same impurity density and are 0ept at

room temperature

A. both will have e;ual value of resistivity

B. both will have e;ual neative resistivity


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C. resistivity of ermanium will be hiher than that of silicon

D.

resistivity of silicon will be hiher than that of ermanium

-esistivity of silicon is more than that of ermanium.

2. hen an electric field & is applied to solid and li;uid insulatin materials, the internal field

&i actin at the location of atom is such that

A. &i $ &

B.

&i < &

C. &i = &

D. &i may be e;ual to or less than &

The actual field seen by an atom is larer than applied field.

21. hich element ehibits the property of inertia>

A. -esistance

B. "apacitance

C.Inductance

D. +oth resistance and inductance

Inductance opposes rise and decay of current. 9ence it has the property of inertia.

22. ?or a permanent manetic material

A.the residual induction and coercive field should be lare

B. the residual induction and coercive field should be small


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C. area of hysteresis loop should be small

D. initial relative permeability should be hih

/aterials suitable for permanent manet have lare hysteresis loop.

9ence residual and coercive field are lare.

23. In a coaial cable, braided copper is used for

A. conductor B.shield

C. dielectric D. 8ac0et

+raided material is used for shield.

24. The hysteresis phenomenon in ferromanetic materials eists at all temperatures.

A. True B.?alse

9ysteresis phenomenon eists below ferromanetic curie temperature.

25. Assertion (A): /anetic susceptibility of diamanetic materials is much less than that of

paramanetic materials.

Reason (R): ?or diamanetic as well as paramanetic materials, @r is nearly e;ual to 1.





/anetic susceptibility $ A@r ! 1B9.

?or diamanetic and paramanetic materials manetic susceptibility is very very small and @ r $ 1.


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2. The attraction between the nucleus and valence electron of copper atom is

A. Cero

B.wea0

C. stron

D. either Cero or stron

The valence electron, in copper atom, can be easily detached from nucleus.

2. If the temperature of an etrinsic semiconductor is increased so that the intrinsic carrier

concentration is doubled, then

A. the ma8ority carrier density is doubled

B. the minority carrier density is doubled

C. the minority carrier density becomes 4 times the oriinal value

D.both the ma8ority and minority carrier densities double

*s the intrinsic carrier concentration is doubled, the concentration of both electrons and holes

is doubled.

2:. There is no hysteresis phenomenon is any dielectric material.

A. True B.?alse

9ysteresis phenomenon eists in dielectic materials.

26. The units of @ and @r are

A. 9Dm for both


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B. 9Dm for @r and no units for @

C.9Dm for @ and no units for @r

D. bDm for @ and no units for @r

@r is only a numeric.

3. In metals the valence electron wave functions are stronly perturbed by the presence of

neihbourin atoms.

A.True

B. ?alse

In a metal valence electrons are shared by all atoms.

31. ?or a paramanetic material, susceptiblity increases with increasin temperature.

A. True B.?alse

usceptibility ∝ .

32. 9ydroen is used in

A. lare siCe transformers

B. /"+

C.lare siCe enerators

D. circuit brea0ers

/odem lare siCe enerators have hydroen coolin.

33. Assertion (A): ?erroelectric materials have spontaneous polariCation.

Reason (R): *bove curie temperature, ∈ $ for ferro!electric materials.


B.+oth * and - are true but - is not correct eplanation of *


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+oth * and - are correct. pontaneous polariCation vanishes above ferroelectric curietemperature.

34. If e is the chare of an electron, - is the radius of its orbit and E is the anular velocity of

electron, the manetic dipole moment @m of the orbit is F@mF $ eE-2.

A. True B.?alse

1 @m 1 $ .5 eEr 2.

35. If ∈r ' and ∈r " are the real and imainary parts of comple dielectric constant ∈r , and G is the loss

anle. Then

A.

B.

C. tan G $ ∈' ∈"

D. tan G $ 1 ! ∈'

If ∈r " $ , G $ .

3. Assertion (A): *t a temperature of 1 H, thermionic emission current is about .1 *Dcm2 of

surface.

Reason (R): Thermionic emission current is iven by Ith $ * T 2 e!&wDk T.





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If different values are substituted in the e;uation for Ith the value of emission current comes

out to be about .1 *Dcm2.

3. *t room temperature, the current in intrinsic semiconductor is due to

A. holes

B. electrons

C. ions

D.holes and electrons

+oth electrons and holes contribute to flow of current in semiconductors.

3:. ?erroelectric materials are those which

A. cannot be polariCed

B. have a permanent polarization

C. have αe e;ual to Cero

D. have @ p $

?erroelectric materials have permanent polariCation.

36. Assertion (A): Power loss in a conductor of resistance P $ I2-.

Reason (R): hen a conductor is carryin current with current density # as a result of applied

field &, then heat developedDm3 D second $ #&.





9eat developed depends an power loss.


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4. Assertion (A): ?or iamond, @r $ 1

Reason (R): iamond is a diamanetic material.





?or diamanetic materials @r $ 1.

41. If n denotes principal ;uantum number, the anular ;uantum number l $ , 1... An ! 1B.

A.True

B. ?alse

*nular ;uantum number determines the anular momentum of electron.

42. Assertion (A): In a perfect capacitor, the current density is iven by E ∈&∈' r cosAEt 67B,

where ∈r ' is real part of dielectric constant.

Reason (R): In a perfect capacitor, dielectric losses are Cero.





If dielectric losses are Cero, the current in capacitor leads the applied voltae by 67.

*lso imainary part of is ∈r is Cero.

43.

Assertion (A): ?or a solenoid havin J turns, .

Reason (R): ?or all manetic materials, + increases linearly with I.



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C.* is true but - is false


Increase of + with I is not linear. 9ence - is false.

44. Assertion (A): ?rom the slope of the line in ?iure, we can find permanent dipole moment of the

molecules.

Reason (R): Total polariCation of a polyatomic as is iven by P $ N Aαe αi @2 p D 3k TB&.





The slope of the line in fiure is .

ince the total polariCation is as iven by the epression, we can find the permanent dipole

moment of the molecules from the slope.

45. Assertion (A): If & is available enery state eK and &? is ?ermi level, then probability of enery

state & bein occupied $ .5.

Reason (R): .



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B.+oth * and - are true but - is not correct eplanation of *



& $ &?, f A&B $ .5.

4. If a piece of wood is placed in a manetic field

A.the manetic field will not be affected

B. the manetic lines of force will bend towards the piece

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

D. the flu may increase or decrease

ood is non!manetic.

4. The apparent capacitance at a hih anular fre;uency E of an air cored capacitor havin

capacitance " and inductance L is iven by

A.

B.

C.

D.

The combination can be represented as L and " in series.

.

Therefore, .

4:. The number of valence electrons in donor impurity are


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A.5

B. 4

C. 3 D. 1

onor impurity has 5 valence electrons Awhile silicon has 4 valence electronsB.

9ence donor impurity can donate electrons.

46. In a true valence crystal, the bondin between the atoms is accomplished by the sharin of

valence electrons.

A.True

B. ?alse

harin of valence electons is a characteristic of true valence crystal.

5. hich of the followin are donor impurities>

1. )old

2. Phosphorus

3. +oron

4. *ntimony

5. *rsenic

. Induim

elect the correct answer usin the followin codes

A. 1, 2, 3

B. 1, 2, 4,

C. 3, 4, 5,

D. 2, 4, 5

onor impurities have five valence electrons.


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materials and components section 1

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