Introduction

In this article Important questions with answers for Msc Entrances physics, we will discuss some most important questions of physics along with there answers. These questions are recommended for Msc examination as well as for all graduation level competitive examinations.In this article some important questions covered from semiconductor, pn junction ,diodes etc

Important questions with answers for Msc Entrances

Here are some important questions you need to know for Msc entrance entrance examination by physics –

Q.1 A semiconductor is formed by ..bonds.

(a)Covalent

(b)Electrovalent

(c)co-ordinate

(d)none of above

Answer : Covalent bond

Q.2 A semiconductor has…..temperature coefficient of resistance.

(a)Positive

(b)Zero

(c)Negative

(d)none of above

Answer: Negative (Because of Resistance of semiconductor decrease with increase in temperature)

Q.3 The most commonly used semiconductor is..

(a)Germanium

(b)Silicon

(c)Carbon

(d)Sulphur

Answer : Silicon (First of all sulphur is not a semiconductor and carbon is not used as a semiconductor)

Q.4 A semiconductor has normally … valence electrons.

(a)2

(b)3

(c)6

(d)4

Answer : 4

Q.5 When a pure semiconductor is heated, its resistance…

(a)Goes up

(b)Goes down

(c)Remains same

(d)Can’t say

Answer: Goes down (Because as we increase the temperature the conductivity increases. And resistance decreases And Hence negative temperature coefficient)

Q.6 When a pentavalent impurity added to a semiconductor, it becomes

(a)An insulator

(b)an intrinsic semiconductor

(c)p-type semiconductor

(d) n-type semiconductor

Answer: the N-type semiconductor (because when we add a pentavalent impurity in a semiconductor then it forms four covalent bonds with the center atom. But one extra electron remains unbonded which tends to increase the conductivity of semiconductor and becomes an n-type semiconductor)

Q.7 Addition of pentavalent impurity to a semiconductor creates many-

(a)Free Electrons

(b)Holes

(c)Valence electrons

(d)Bound electrons

Answer: Free electrons

Q.8 A pentavalent impurity has… Valence electrons

(a)3

(b)4

(c)5

(d)6

Answer: 5

Questions you should must read

Q.9 An n-type/p-type semiconductor is…

(a)positively charged

(b)Negatively charged

(c)Electrically neutral

(d)None of the above

Answer: Electrically charged (this is because of the fact that an n-type or p-type semiconductor number of holes and electrons are in equal number.)

Q.10 A trivalent impurity has…valence electrons

(a) 4

(b) 5

(c) 6

(d) 3

Answer: 3

Q.11 Addition of a trivalent impurity to a semiconductor creates many…(trivalent B, Al, Ga, In, Ti)

(a) Holes

(b) Free electrons

(c) Valence electrons

(d) Bound electrons

Answer: Holes (because in trivalent impurity there are three electrons in valence electrons which creates a hole.

Q.12 A hole in a semiconductor is defined as…

(a) A free electron

(b) Electron Vacancy

(c) A free proton

(d) A free neutron

Answer: Electron Vacancy

Q.13 As the doping to a pure semiconductor increases, the bulk resistance of the semiconductor…

(a) Remains the same

(b) Increases

(c) Decreases

(d) None of the above

Answer: Decreases

(Because of carrier  concentration increases)

Other

Q.14 In a semiconductor, current conduction is due to…

(a) Only holes

(b) Only free electrons

(c) Holes and free electrons

(d) None of the above

Answer: Holes and free electrons

Q.15 The random motion of holes and free electrons due to thermal agitation is called…

(a) Diffusion

(b) Pressure

(c) Ionization

(d) None of the above

Answer: Diffusion

Q.16 The battery connections required to forward bias a pn junction are…

(a) +ve terminal to p and -ve terminal to n

(b)-ve terminal to p and +ve terminal to n

(c)-ve terminal to p and-ve terminal to n

(d) None of the above

Answer: +ve terminal to p and -ve terminal to n

Q.17 In the depletion region of a pn junction, there is a shortage of…

(a) Acceptor ions

(b) Holes and electrons

(c) Donor ions

(d) None of the above

Answer: Holes and electrons

Q.18 A reverse bias pn junction has…

(a) Very narrow depletion layer

(b) Almost no current

(c) Very low resistance

(d) Large current flow

Answer: Almost no current

(But small current called reverse saturation current)

Q.19 A  Junction acts as a…

(a) Controlled switch

(b) Bidirectional switch

(c) Unidirectional switch

(d) Nonw of the above

Answer: Unidirectional switch

Q.20 The leakage current (order of μA) across a pn junction is due to

(a) Minruity carriers

(b) Majority carriers

(c) Junction capacitance

(d) None of the above

Answer: Minority carriers

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