1. UNIT- IV SOLID STATE PHYSICS

2. 1)Electrical conductivity in between conductors & insulators is a) high conductors b) low conductors c) Semiconductors d) partial conductors 2)The main distinction between conductors, semiconductors & insulators is Concerned with a) Binding energy of electrons b) Work function c) Temperature coefficient of resistance d) Width of forbidden band

3. 3)Why metals are good conductors of heat than insulators because a) They contain free electrons b) Their atoms are relative far apart c) Their atoms collide frequently d) They have reflecting surface 4) If n-p-n transistor is used as an amplifier, then a) Electrons move from base to collector b) Holes move from base to collector c) Electrons move from collector to base d) Holes move from collector to base

4. 5) Diamond acts as an a) Conductor b) Insulator c) Semiconductord) None of the above 6) The width of the -----------------------is an important factor in determining whether the materials are conductors, semiconductors & Insulators. a) Valence band b) conduction band c) Forbidden band d) band energy 7) The resistivity of semiconductor varies from a) 10 -12 to 10 9 Ωcm b) 10- 14 to 10 8 Ωcm c) 10 -10 to 10 8 Ωcm d) 10 -15 to 10- 20 Ωcm

5. 8)For an N-type semiconductor, the Hall coefficient is a) Negative b) positive c) One d) zero 9) In NPN transistor the arrow head on emitter represents that The conventional current flows from a) base to collector b) base to emitter c) Emitter to collector d) emitter to base

6. 10)Choose the only false statement from the following a) In conductors valence & conduction band may overlap. b) Substances with energy gap of the order of 10 eV are insulators c)The resistivity of semiconductor increases with rise intemperature. d) The conductivity of semiconductor increases with rise in temperature. 11) The electrical conductivity of semiconductor increases when electromagnetic Radiation of wavelength shorter than 2480 nm is incident on it. The band gap in eV for semiconductor is a)1.1eV b) 2.5eV c) 0.5eV d) 0.7eV

7. 12)In a semiconducting material the mobilities of electron & hole are µ e and µ h respectively which of the following is true? a) µ e › µ h b) µ e =µ h c) µ h › µ e d) µ e ›0, µ h ›0 13) One way in which the operation of an NPN transistor differs from that of a PNP transistor is that a) the emitter junction is reversed biased in NPN b) the emitter junction injects minority carriers into the base region of the PNP c) the emitter injects holes into the base of the PNP & electrons into the base region of NPN d) the emitter injects holes into the base of NPN

8. 14)NPN transistors are preferred to PNP transistors because they have a) Low cost b) low Dissipation energy c) Capable of handling large power d) Electrons have high mobility than holes & hence high mobility of energy 15) If the base & collector of a transistor are in forward bias, then it can not be used as a) a switch b) an amplifier c) an Oscillator d) all the above 16) In NPN transistor the arrow head on emitter represents that the conventional current flows from a) base to emitter b) emitter to base c) emitter to collector d) base to collector

9. 17)When two semiconductors of p-type & n-type are brought in contact with each other, the P-N junction formed behaves like a) an oscillator b) a condenser c) an Amplifier d) a Conductor 18) On increasing the reverse voltage in a P-N junction diode the value of reverse current will a) Gradually increase b) suddenly increase c) remains constant d) gradually decrease 19) The forbidden energy gap in an insulator is of the order of a) 1 MeV b) 0.1 MeV c) 4 MeV d) 5 MeV

10. 20)In an N-type semiconductor, doner valence band is a) above the conduction band of the host crystal. b) close to the valence band of the host crystal. c) close to the conduction band of the host crystal. d) below to the valence band of the host crystal 21) Semiconductor devices are a) temperature dependant.b) voltage dependant. c) current dependant.d) none of these.

11. 22)Which of the following properties can be different along different directions in a crystalline solids a)Electrical conductivity b) Refractive index c) Mechanical strength.d) All of these. 23) Which of the following when added as an impurity into the silicon produces n-type semiconductor? a) P b) Al c)Bd) Mg 24)At O o K, intrinsic semiconductor behaves as 1 a) a perfect conductorb) a super conductor c) a semiconductor d) a perfect insulator

12. 25) In n e & n h are the number of electrons & holes in a semiconductor heavily doped with phosphorus, then a)n e >>n h b) n e <<n h c)n e <n h d) n e =n h 26) An n type & p type silicon can be obtained by doping pure silicon with a) Arsenic & Phosphrousb) Indium & Aluminium c) Phosphrous & Indiumd) Aluminium & Boron 27) In forward bias, the width of potential barrier in a p-n junction diode a) increases b) decreases c) remains constantd) first (a) then (b)

13. 28)Deplection layer consists of a) electrons b) protons c) mobile ions d) immobile ions 29) The major constituent of transistor are a) salts b) transistor c) conductors d) semiconductors 30) On reverse biasing the P-N junction,its potential barrier becomes a) narrow b) broad c) zero d) constant

14. 31)The ratio of maximum useful power to ideal power is called as a) Efficiencyb) Open-circuit c) Fill factor d) short-circuit 32) Photoelectric cells convert light energy into a) solar energy b) mechanical energy c) electrical energyd) kinetic energy 33) The Fermi level in intrinsic semiconductor lies exactly at the -- of the forbidden band. a) above b) below c) middle d) none of these

15. 34)In the P-type semiconductor, the hole concentration in valence band is ------ than the electron concentration in conduction band. a) Less b) equal to c) Greater d) all of these 35) Barrier potential of a p-n junction diode does not depend on -- a) temperature b)forward bias c) doping density d) diode design 36) Reverse bias applied on a junction diode------- a) raises the potential barrier b) increases the majority carrier current c) increase the minority carrier current d) lowers the potential barrier

16. 37)A semiconductor is characterized by ------- a) completely filled V.B. b) partially filled C.B. c) overlapping between V.B. and C.B. d) none of these 38)In a PN junction diode -------- a) high potential at N side and low potential at P side b) high potential at P side and low potential at N side c) P and N both are at same potential d) undetermined.

17. 39) Which is the correct relation for forbidden energy cap in conductor, semi-conductor and insulator? a) ∆Eg c > ∆Egs sc > ∆Eg insulator b) ∆Eg insulator > ∆ Egs sc > ∆Eg conductor c) ∆Eg conductor > ∆Eg insulator > ∆ Egs sc d) ∆ Egs sc > ∆ Eg conductor > ∆Eg insulator 40) When the temperature of n- type semiconductor is increases ------ a) net negative charge is increased b) net charge is zero c) minority carriers are decreased d)none of the above is true

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