Engineering Physics

1) The electrical conductivity of a semiconductor at absolute zero of temperature is zero

2) At room temperature, the conduction band electrons are equal to that of valence band holes in
an intrinsic semiconductor

3) If m*h > m*e, then the position of Fermi energy level is just above the center of forbidden energy gap

4) Dual nature [particle and wave] of matter was proposed by de Broglie

5) Spectral line splitting due to the influence of magnetic fields is called Zeeman Effect

6) The Zeeman Effect without the spin of the electron is called Normal Zeeman Effect

7) In semiconductors with the increase in temperature the resistance Decreases

8) Conduction band contains free electrons

9) Semiconductors are material in which conductivity is None of the options

A .Greater than conductivity of a conductor B . less than conductivity of an insulator

C. Equal to conductivity of a conductor D. None of the above

Answer D

10) All semiconductors in their last orbit have 4 electrons

11)  Hall Effect is associated with Semiconductors

 12) What was demonstrated by G. P. Thomson?

Diffraction of electrons

13)  If line spectrum is subjected to magnetic field, the line splits into a number of components symmetrically
distributed about the original line. This effect is known as, Zeeman effect

14)  When a beam of monochromatic light passed through organic liquids, the scattered light contained other
frequencies in addition to that of the incident light. This effect is known as, Raman Effect

 15) In Hall Effect if magnetic field is applied along X-axis, current is flowing along Y axis, then in what
direction the hall voltage would develop? Perpendicular to magnetic field direction as well as current
flow direction

16)  Silicon and Germanium element have four valence electrons

17)  Valence electrons are the Electrons present in the outermost orbit

 18) A Germanium atom contains Four valance electron

 19) Free electrons exist in Conduction band

 20) The energy band occupied by valence electrons that are incorporated into covalent bonds is
called Valence band

21) The energy band hosing the free electrons capable of electrical conduction is called the Conduction
band
 22) The energy interval between the top edge of valence band and the bottom edge of the conduction band
is Forbidden band gap 

 23) Depending of existence and width of which band the solids are classified as conductors, semiconductors,
and insulators?

Forbidden band gap 

24) At absolute zero temperature, in insulators and semiconductors The valence band is full and
conduction band is empty

25) The valence band and conduction band are separated by Forbidden band gap

26)  Materials which show negligible conductivity at 0K but exhibit significant Conductivity at normal
temperatures are called as, Semiconductors

 27) In semiconductor, the forbidden gap Eg typically From 0.5 eV to 1.5 eV

28)  In semiconductors, the empty states left behind in the valence band assume particle character and act as
charge carriers. These empty states are called as, Holes

29)  The uppermost filled energy level in a conductor at 0K -Fermi energy

30)  The maximum energy energy that an electron can have in a conductor at 0K

-Fermi energy

31)  The average energy possessed by the electrons which participate n conduction process in conductors at
temperatures above 0K Fermi energy

32) The class of solids in which, at normal temperatures, a significant number of electrons are thermally
excited from valence band to conduction band and an equal number of holes are produced in the valance band
is............Semiconductors

33)  Chemically pure semiconductors are known as Intrinsic semiconductors

34)  A semiconductor is considered to be pure when …There is less than one impurity atom in a billion
host atoms.

 35) Intrinsic semiconductors have Low conductivity

36)  An introduction of impurity atoms in an perfect semiconductor gives rise to Extrinsic semiconductors

37)  An intentional introduction of controlled quantity of impurity into an intrinsic semiconductor is called as

Doping

38)In an intrinsic semiconductor, the concentration of electrons and holes will be equal

39)  The process that generates carriers in an intrinsic semiconductors Thermal process

40) The electrical conductivity increases when an intrinsic semiconductor is doped with suitable impurity.
Such semiconductor is known as Extrinsic semiconductors

 41)Semiconductor doped with pentavalent impurities become 'n' type semiconductor

42) Semiconductor doped with trivalent impurities become 'p' type semiconductor

43) pentavalent impurities are called as  Donor impurities

45) In n-type semiconductor, donor levels are near the edge of conduction band.

46) In p-type semiconductor, acceptor levels are near the edge of valance band

 47) The more numerous carriers in an extrinsic semiconductor are known as,

Majority carriers

 48) The less numerous carriers in an extrinsic semiconductor are known as,

Minority carriers

49)   The wavelength λ associated with a particle of mass m moving with velocity v is given by

h/mv

50) The product of uncertainties between position and momentum is given by ΔxΔp=h

 51)The equation of wavelength of matter wave was derived by de-broglie

52) The wavelength of electron accelerated though the potential V is Inversely proportional to square root
of potential V

53)The velocity of matter wave is Larger than the velocity of light

54)  The equation of motion of matter wave was derived by Schrodinger

 55) The particle is specified by Mass and Velocity

56) The particle is specified by Mass and Momentum

57) The wave is specified by Frequency, Wavelength, Amplitude

 58) De-Broglie wavelength of a particle with momentum p is h/p

 59) The velocity of matter waves depend upon Velocity of Particle

60) In Fermi-Dirac Distribution function, the probability that the energy level E occupied by

Electron

61) Fermi level for extrinsic semiconductor depends on

A Donor element B Impurity concentration

C Temperature D All of these

 62)  When a Pentavalent impurity is added to pure semiconductor it becomes N-Type semiconductor

 63) Addition of Pentavalent impurity to a Semiconductor creates Free Electrons

64)  A hole in a Semiconductor is defined as a In-complete part of an electron pair bond

 65) Fermi energy level for intrinsic semiconductors lies Close to valence band

66)  Fermi energy level for p-type extrinsic semiconductors lies Close to conduction band
67) In an n type semiconductor, at T=0K, Fermi level lies midway between the donor levels and the
bottom of the conduction band

68) In an p type semiconductor, at T=0K, Fermi level lies midway between the acceptor level and the top
of the valence band

69)  The Fermi-Dirac distribution function gives fractional occupancy of the energy states

70) Matter waves are present when particles are in motion

 71 )The wave function Ψ of the particle is a solution to the wave equation

72) Schrodinger time dependent wave equation is given by HΨ =EΨ

73) If the Hall coefficient is negative then the semiconductor is n-type

74) The sign of Hall coefficient in p type semiconductor is positive

75) In G. P. Thomson experiment for diffraction, the sample used for diffraction is,

Thin film of gold or silver or aluminum

76)Which of the following is not the characteristic of a LASER source Divergence

 77)What is the full form of LASER Light amplification by stimulated emission of radiation

 78)Which of the following are the characteristics shown by laser beam

A Coherence B High intensity

C monochromatic  D All of these

79 )As compared Laser, ordinary light does not have

A monochromaticity B coherence C Large intensity

D. All of these

80) Taking atoms from excited state to ground state by photon hitting the excited atom is known
as, stimulated emission 

81) Atoms in the ground state absorb the energy photon and rose to excited state. This interaction is known
as, Absorption of radiation

82) The natural tendency of atoms in the excited state to release the photon and return to the ground state is
known as, spontaneous emission

83) Population Inversion means, More number of atoms in the excited state

84) The method of raising the particles from lower energy state to higher energy state so that population
inversion achieved is called,                 

Pumping mechanism

85) An energy state which has longer life time as compared to excited state is known as

Metastable state

86) An energy state which have highest life time and in which atoms are most stable is,
 Ground state

87) Population inversion is completed in certain medium so that laser beam can be produced. Such a medium
is known as,

Active medium

88) The emission responsible for producing laser is,

Stimulated emission

 89) Population inversion in preparing a laser beam can be achieved

when one of the excited states is more populated than the ground state

90) Stimulated emission process is favored whenever

Population inversion is attained

91) In a three level pumping mechanism, which one of the following energy state is not present? non
radiative transition state

92) In a three level pumping mechanism, how many energy states are present? three

93) In a four level pumping mechanism, how many energy states are present?

four

94) The laser action takes place when a transition of atoms occurs from

Metastable state to any lower energy state

95) In ruby laser which part acts as an active medium material

Ruby rod 

 96) Ruby laser is a Solid state laser

 97) Ruby laser is a_ Three level laser system

98)  In Ruby laser optical pumping is achieved by _ Xenon Flash lamp

99)  Ruby laser is a pulsed laser source

100) Ruby rod is made up of Aluminum oxide Al2O3 + Chromium Oxide Cr2O3

Optical pumping

 The wavelength of the emitted light in Ruby laser is6943 Å

 He-Ne Laser is a Gaseous laser

  He-Ne laser is a _ Continuous laser

 He-Ne Laser is a Four level laser system

  In He-Ne laser system, the helium and neon gases respectively maintained at a ratio 10:1

 In He-Ne laser, neon atoms obtain energy On collision from Helium atoms

 In He-Ne laser, population inversion is achieved by Electrical pumping

 The active medium for a He-Ne laser is mixture of He and Ne atoms

 The wavelength of the emitted light in He-Ne laser is 6328 Å

 Which of the following is a gas laser? He-Ne laser

 Which of the following is a solid state laser? Ruby laser

 In a semiconductor laser, the active medium is heavily doped p and n region

 In a semiconductor laser, the p-n junction is connected in forward bias

 In a semiconductor laser, the population inversion is achieved in depletion layer  

 Semiconductor laser can be achieved in  Ga-As   

 The structure of optical fiber from centre to outside is, Core, cladding and Protecting Sheath

  An optical fiber is based on the principal of total internal reflection

 The sheath of an optical fiber enables

A to prevent from mechanical abrasions

B to prevent interaction with other signals. C to prevent from moisture trapping

D.all of these

In case of optical fiber, the innermost region through which the signal light is guided is known as,

Core

 In case of optical fiber, the core is surrounded by a coaxial middle region known as, Cladding

 In case of optical fiber, the outermost region known as, Protecting Sheath

 For optical fiber to transmit the signal, the necessary condition is given by

refractive index of core should be greater than refractive index of cladding

  In step index fiber, the refractive index Changes abruptly at the core cladding interface

 A number which defines the light gathering capacity of an optical fiber is known as

numerical aperture

 In case of optical fiber, the number which is defined as the sin of the acceptance angle is called as,

numerical aperture

 The angle of incidence made by the ray with the axis of the optical fiber such that it strikes at critical angle at
core cladding interface is known as the -Acceptance angle

  A maximum angle that a light signal can have relative to the axis of the fiber, get transmitted in the fiber and
propagate down the fiber is known as, Acceptance angle

 The correct expression for the acceptance angle is, where n1 and n2 are refractive indices of core and
cladding,

 The light signal incident at acceptance angle gets completely transmitted in the fiber 

   The light rays contained within the core having the full angle 2 are accepted and transmitted along the
fiber. This cone is called as, Acceptance cone

 If  n1 is refractive index of core and n2 is refractive index of cladding, then the expression for numerical
aperture of the optical fiber is,

Acceptance cone

 Which one of the following is not a class of optical fiber,

Single mode graded index fiber

 Which of the following is the application of optical fiber?

A In communication applications

B In military applications, by replacing heavy wires with light weight cables

C In temperature and pressure sensors as couplers 

D All of these 

Answer D All of these

 What is nature of output of 0.05% Cr2O3 doped ruby laser? pulsed    

 Acceptance angle is the Maximum angle of incidence

 Probability of spontaneous emission increases rapidly with increase of

Energy difference between two states    

 Resonant cavity in semiconductor-lasers consists of Intrinsic region

 Pumping source preferred for gaseous lasers is Electrical Pumping

 The time during which a particle can remain in the excited state is Life time
 In the process of excitation, the energy is absorbed

 In the process of de-excitation, photon is emitted

 Spontaneous emission is  incoherent

 In stimulated emission the incident photon and emitted photon are

Coherent with each other

 In inverted population always the population of higher energy state is

More than lower energy state

 Ruby is a crystal of Al2O3

 In Ruby crystal aluminum atoms are replaced by Cr2O3

 Ruby crystal contains the Chromium about 0.05%

 Colour of Chromium is Pink

 Dimensions of the Ruby rod are 4 cm length, 0.5 cm in diameter

The Ruby rod is surrounded by a helical Xenon flash tube

Population inversion occurs in  non-equilibrium state

Transmission loss of optical fiber compared to copper wire is lower

Step index fiber sustains only

Single mode of propagation                             

Multimode of propagation

Compared to copper cable the information carrying capacity of optical fiber system is Superior

In optical fiber, ray undergoes total internal reflection only if angle of incidence is greater than critical
angle

 In fiber optics, the signal source is Light waves.

 The main drawback of ruby laser is that the output beam is not continuous

  The main advantages of gas lasers are Monochromatic, pure spectrum

The gas laser consist of a fused Quartz tube

Mixture of He : Ne is filled in the tube with pressure of 1.0: 0.1 mm of Hg

 In Gas laser tube is filled with majority of He and minority of Ne

 In Gas laser, excited He atoms colloid with Ne atoms

Excited state has life time 10-8 sec

 10-3 sec is the life time of metastable state

 Semiconductor diode laser have sides of the order of 1mm

 To achieve population inversion in a semiconductor diode, pn junction should be heavily doped

 Laser is a device which gives output in the form of an intense, coherent and monochromatic beam of light

  In a p-n junction diode laser, the role of pumping agent is played by forward current

An optical fiber has a shape of cylindrical

An optical fiber consists of an inner cylinder called the core

 In optical fiber, light carried by  Core

Numerical aperture of fiber is a measure of light

Gathering power

 The problem of satisfactory speech at the music in a hall is tackled by the scientist

Sabine

 Acoustics is the science which deals with planning of a building to provide best

Audible sound

 Branch of engineering which deals with better audibility of sound is called as…

Architectural acoustics

 In case of good acoustics the reverberation time for music be 1 to 2 sec

 In case of good acoustics the reverberation time for speech should be 0.5 to 1 sec

 Persistence of sound after the source has stopped to emit the sound is called as

Reverberation

 The coefficient of absorption of a material is defined as the ratio of the sound energy absorbed by the
surface to that of the total incident sound energy on the surface

 The absorption coefficient is measured in  O.W.U.

 The reverberation can be controlled by having full capacity of audience and the walls are lined with
absorbent materials

 The materials used to reduce the reflection of sound waves in a room are known as, sound Absorbing
materials

 The walls of a hall built for music concerns should absorb sound

 Relation between intensity of original sound (IO) & the intensity of sound after reverberation (It) is It/IO=10-6

 The sound waves having frequency greater than 20 KHZ are known as

Ultrasonic Waves

 Compared to audible sound, wavelength of ultrasonic waves is  small

 In Magnetostriction method, rod used is made up of  Ferromagnetic material

 In Magnetostriction method, the field applied on the ferromagnetic rod is, magnetic field

 In Piezo electric method, the field applied on the crystal is, Electric field

  In Magnetostriction method, resonance occurs when frequency of the alternating current and the natural
frequency of the rod are equal

 The ferromagnetic rod sends out ultrasonic waves, if the applied frequency and ultrasonic frequency are in
the same order

 In Magnetostriction method, a short nickel rod is clamped at the Center

 In Magnetostriction method, resonant vibrations occur when the natural frequency of the rod is same as the
frequency of the Plate circuit

 In Piezoelectric method, vibrations are produced when the natural frequency of the crystal coincides with the
frequency of the Electric oscillations

 Ultrasonic waves are produced when the quartz crystal is set into mechanical Vibrations

 By using Piezoelectric method ultrasonic waves are obtained up to a frequency of 500 KHZ

 Sound waves having frequency less than 20 Hz are called as Infrasonic

 The speed of propagation of ultrasonic waves increases with increase in  Frequency

 Ultrasonic waves are the waves having Small wavelength, greater frequency

 The time for which the sound persists in the hall is called as Reverberation Time

 The unit of absorption coefficient is Open Window unit (OWU ) 

What will be the reverberation time of the hall if the volume of the hall is 1200 meter cube and total
absorption in hall is 110 metric Sabine? 1.8 S

 A hall has a volume of 7500 meter cube. It is required to have reverberation time of 1.5 seconds. What
should be the total absorption in the hall? 825 OWU

 The factors that are to be considered in acoustical design of the hall are,

A Site selection

B Volume, shape and seating arrangement of the hall 

C Proper reverberation and reverberation time

D All of these

Answer D All of these

 The classes of acoustical materials are,

A Porous and composite material

B Resonant panels  
C Cavity resonator 

D All of these

Answer D All of these

 The class of acoustical material which is effective in the higher frequencies are

Porous material

 The class of acoustical material which is effective at lower frequencies are

Resonant panels

 The class of acoustical material which can be designed to absorb any specific frequency is called as  Cavity
resonator

 The class of acoustical material which combines the functions of all type of acoustical materials is known
as, Composite absorbers

  The sound heard due to reflection from an obstacle is known as Echo

 The persistence of audible sound after the source has stopped to emit the sound is known as Reverberation

 The time taken by sound to fall to one millionth of its intensity and become inaudible, when the source
stopped sounding is known as Reverberation time

 The frequency of ultrasonic’s is above 20,000 Hz

  Ultrasonic waves are Longitudinal

 Ultrasonic waves are Mechanical vibrations

 Bats detect obstacles in their path by producing pulses of ultrasonic waves

 Ultrasonic waves can be used to determine the depth of sea by echo-sounding because of their

A Large velocity B Small velocity

C Small wavelength D Large wavelength

Answer C Small wavelength

 Out of the following, which is not a property exhibited by ultrasonic waves,

A The wavelength of ultrasonic waves is very small B They produces cavitation effect in liquids

C ultrasonic waves has a great penetration power D They are less energetic

Answer D they are less energetic

 The full form of SONAR application of ultrasonic waves is, Sound navigation and ranging

 The applications of ultrasonic waves are

A Echo sounder and SONAR B Non destructive testing

C Welding, soldering and Cleaning D All of these

Answer D All of these

 When a rod of ferromagnetic material, is kept in a magnetic field parallel to its length, the rod suffers a
change in its length. This phenomenon is known as,

Magnetostriction effect

 The range of sound wave frequencies which human ear can hear is known as,

audible range