Download The electrical conductivity of a semiconductor at absolute zero of

The electrical conductivity of a semiconductor at absolute zero of temperature is zero
At room temperature, the conduction band electrons are equal to that of valence band holes in an intrinsic
semiconductor
If m*h > m*e, then the position of Fermi energy level is just above the center of forbidden energy gap
Dual nature [particle and wave] of matter was proposed by de Broglie
Spectral line splitting due to the influence of magnetic fields is called Zeeman Effect
The Zeeman Effect without the spin of the electron is called Normal Zeeman Effect
In semiconductors with the increase in temperature the resistance Decreases
Conduction band contains free electrons
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
All semiconductors in their last orbit have 4 electrons
Hall Effect is associated with Semiconductors
What was demonstrated by G. P. Thomson?
Diffraction of electrons
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
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
Hall effect measurement helps us to get
Measurement of magnetic field
Sign and Concentration of charge carrier
Mobility of charge carriers
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
Silicon and Germanium element have four valence electrons
Valence electrons are the Electrons present in the outermost orbit
A Germanium atom contains Four valance electron
Free electrons exist in Conduction band
The energy band occupied by valence electrons that are incorporated into covalent bonds is called Valence
band
The energy band hosing the free electrons capable of electrical conduction is called the Conduction band
The energy interval between the top edge of valence band and the bottom edge of the conduction band is
Forbidden band gap
Depending of existence and width of which band the solids are classified as conductors, semiconductors, and
insulators?
Forbidden band gap
At absolute zero temperature, in insulators and semiconductors The valence band is full and conduction band
is empty
The valence band and conduction band are separated by Forbidden band gap
Materials which show negligible conductivity at 0K but exhibit significant Conductivity at normal temperatures
are called as, Semiconductors
In semiconductor, the forbidden gap Eg typically From 0.5 eV to 1.5 eV
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
The uppermost filled energy level in a conductor at 0K -Fermi energy
The maximum energy energy that an electron can have in a conductor at 0K
-Fermi energy
The average energy possessed by the electrons which participate n conduction process in conductors at
temperatures above 0K Fermi energy
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
Chemically pure semiconductors are known as Intrinsic semiconductors
A semiconductor is considered to be pure when …There is less than one impurity atom in a billion host
atoms.
Intrinsic semiconductors have Low conductivity
An introduction of impurity atoms in an perfect semiconductor gives rise to Extrinsic semiconductors
An intentional introduction of controlled quantity of impurity into an intrinsic semiconductor is called as
Doping
In an intrinsic semiconductor, the concentration of electrons and holes will be equal
The process that generates carriers in an intrinsic semiconductors Thermal process
The electrical conductivity increases when an intrinsic semiconductor is doped with suitable impurity. Such
semiconductor is known as Extrinsic semiconductors
Semiconductor doped with pentavalent impurities become 'n' type semiconductor
Semiconductor doped with trivalent impurities become 'p' type semiconductor
pentavalent impurities are called as Donor impurities
trivalent impurities are called as Acceptor impurities
In n-type semiconductor, donor levels are near the edge of conduction band.
In p-type semiconductor, acceptor levels are near the edge of valance band
The more numerous carriers in an extrinsic semiconductor are known as,
Majority carriers
The less numerous carriers in an extrinsic semiconductor are known as,
Minority carriers
In case of Raman effect the lines on lower frequency side are more intense and called as,
Stokes lines
In case of Raman effect the lines on higher frequency side are less intense and called as,
Anti - Stokes line
Stokes and anti Stoke lines are observed in Raman effect
Raman effect can be observed in Benzene
Which of the following is magneto-optical phenomenon Zeeman effect
The simplest splitting in Zeeman effect is obtained with Strong magnetic field
The complex splitting in Zeeman effect is obtained with Weak magnetic field
In case of Zeeman effect, longitudinal view reveals Doublet
In case of Zeeman effect, transverse view reveals Triplet
In Raman effect, in addition to original line New lines symmetric to both sides of mean line are observed
In Zeeman effect, splitted spectral line are Circularly polarized
The wavelength associated with a particle of mass m moving with velocity v is given by
h/mv
The product of uncertainties between position and momentum is given by
p=h
The equation of wavelength of matter wave was derived by de-broglie
The wavelength of electron accelerated though the potential V is Inversely proportional to square root of
potential V
The velocity of matter wave is Larger than the velocity of light
The equation of motion of matter wave was derived by Schrodinger
The particle is specified by Mass and Velocity
The particle is specified by Mass and Momentum
The wave is specified by Frequency, Wavelength, Amplitude
The time-independent Schrödinger equation is a partial differential equation
De-Broglie wavelength of a particle with momentum p is h/p
The velocity of matter waves depend upon Velocity of Particle
In Fermi-Dirac Distribution function, the probability that the energy level E occupied by
Electron
Fermi level for extrinsic semiconductor depends on
A Donor element
B Impurity concentration
C Temperature
D All of these
Answer D
When a Pentavalent impurity is added to pure semiconductor it becomes N-Type semiconductor
Addition of Pentavalent impurity to a Semiconductor creates Free Electrons
A hole in a Semiconductor is defined as a In-complete part of an electron pair bond
Fermi energy level for intrinsic semiconductors lies Close to valence band
Fermi energy level for p-type extrinsic semiconductors lies Close to conduction band
The intrinsic charge concentration
Is independent of Fermi level
Has an exponential dependence on the band gap value Eg
Strongly depends on the temperature
The Fermi level in an intrinsic semiconductor may be considered as independent
In an n type semiconductor, at T=0K, Fermi level lies midway between the donor levels and the bottom of
the conduction band
In an p type semiconductor, at T=0K, Fermi level lies midway between the acceptor level and the top of the
valence band
The Fermi-Dirac distribution function gives fractional occupancy of the energy states
Matter waves are present when particles are in motion
The wave function
of the particle is a solution to the wave equation
Schrodinger time in-dependent wave equation is given by
2 +8 2m/h2(E-V) =0
Schrodinger time dependent wave equation is given by H
=E
Identify the properties of wave function
Both Normalize and It must be single valued
To prepare a n type semiconductor, the element to be added with tetra valant element is
Pentavalent element
To prepare a p type semiconductor, the element to be added with tetra valant element is
Tri valant element
If the Hall coefficient is negative then the semiconductor is n-type
The sign of Hall coefficient in p type semiconductor is positive
In G. P. Thomson experiment for diffraction, the sample used for diffraction is,
Thin film of gold or silver or aluminum
Raman effect was discovered while study of scattering of light by liquids
Zeeman Effect is a magneto-optic phenomenon which provides a link between spectroscopic and magnetic
properties of elements
The range of critical length below which Nanomaterials begin to demonstrate new physical or chemical
phenomenon is in between 1 to 100 nm
The tensile strength of a carbon nano-tube is 100 times that of steel
The ratio of thermal conductivity of silver to that of carbon nanotubes is 1: 10
Nano material is an emerging branch of science for designing tools and devices of size:
1 to 100 nm
Nanomaterials are a science of creation of:
Functional materials
Control on the nanometer length scale
Exploitation of properties
All of the above
Nano science involves the manipulation of materials on Atomic Scale, Molecular Scale
Micro molecular Scale
The change in the properties of Nanomaterials as compared to bulk is because of
Both Large surface area to volume ratio and Quantum confinement
Materials that are Nano scale in one dimension and are extended in the other two dimensions are
Thin film
Materials that are Nano scale in two dimensions and are extended in one dimension include
Both Nano tubes and Nano wires
Materials that are Nano scale in three dimensions are Nano particles
The properties of Nanomaterials that differ significantly from the bulk are increased
Both Relative surface area and Quantum effect
Greater proportion of atoms are found on the surface as the particle decreases in size
The quantum effect starts dominating the properties of matter, as the materials particle size reduces to nano
scale
The Nanomaterials are ________ in nature Hard
The Nanomaterials are chemically Active
The Nanomaterials are ductile at High temperature
In nanometer size range, the hardness increases with Decrease of particle size
The density of Nanomaterials is ____________ as compared to its bulk density Lowered
Melting temperature of nano Particles gets __________ as compared to bulk melting point
Reduced
In magnetic properties of Nanomaterials below the critical size, material prefers to be
Single domain
__________ play an important role in the magnetic properties of nanostructures
Surface and interfaces
The surface to volume ratio is _______ in Nanomaterials Very large
In Nanomaterials ionization potential is ________ when compared with that of the bulk Higher
The bulk material when reduced to Nanomaterials will show _____ physical and chemical properties
Different
Nanomaterials can be synthesized by Top-down approach, Bottom-up approach
Gold nono Spheres of 100nm appear Orange
Nanomaterials was brought into day light by delivering lectures by Feynman
______ are the extensions of bucky balls
Carbon nano tubes
As the substance change from bulk to nano range they show the change in the properties like,
Opaque material is converted in to transparent
Inert material start behaving like catalysts
Insulators become conductors
The optical properties of nano particles include
Opaque substances are converted into transparent material
Colors of nano particles depend on the particle size
nano particles exhibits photoluminescence but bulk material will not show this effect
The change in the properties of Nanomaterials as compared to bulk is because of
Large surface area to volume ratio
quantum confinement
In Nanomaterials with decrease of size the inter-atomic spacing Decreases
Nanoparticles are transparent
The single domain magnetic particles which do not show coercivity or hysteresis are known as
super-paramagnetic particle
Which one of the following is a physical process of synthesis of nanoparticles?
A sol gel method
B Chemical vapor deposition
C Mechanical Ball milling
D None of these
Answer C
The method in which small balls are allowed to rotate around a drum and drop on the solid enclosed in drum so
that the size of solid is reduced to nano scale is known as,
A sol gel method
B Chemical vapor deposition
C Mechanical Ball milling
D None of these
Answer C
The change in the property of material occurs at nanoscale due to the reason,
A High surface to volume ratio
B More chemical reactivity
C interaction with the environment change
D All of these
Answer D
Which one of the following is not a physical process of synthesis of nanoparticles?
A sol gel method
B Sputter deposition
C Mechanical Ball milling
D Physical vapor deposition
Answer A
Which one of the following is not a chemical process of synthesis of nanoparticles?
A sol gel method
B collide suspension
C inverse micelles
D Physical vapor deposition
Answer D
Which one of the following is a chemical process of synthesis of nanoparticles?
A sol gel method
B Physical vapor deposition
C Mechanical Ball milling
D Laser ablation
Answer A
Mechanical Ball milling is a
A top down approach
B bottom up approach
C top down approach and bottom up approach
D None of these
Answer A
In top down approach of nanoparticles synthesis,
A start with large structure and is made nano form
B starts with individual atom and made nano structures
C starts with nano particles and is made still smaller
D None of these
Answer A
The synthesis method in which, nanoparticles are deposited from the gas phase by heating the material and
depositing on a surface under vacuum, is known as,
A sol gel method
B Chemical vapor deposition
C Mechanical Ball milling
D Laser ablation
Answer B
The synthesis method in which, ions are accelerated towards the surface of the target, causing atoms of the
source material to break off from the target and condense on the substrate is known as,
A sol gel method
B Chemical vapor deposition
C Mechanical Ball milling
D Sputtering
Answer D
The synthesis method in which, high intensity laser beam is focused on target material, target material
converted in to plasma and condense on the substrate at room temperature is known as,
A sol gel method
B Chemical vapor deposition
C Mechanical Ball milling
D Laser ablation
Answer D
Which of the following is not a stage of Sol gel synthesis technique of nanoparticles?
A Agglomeration
B Condensation
C Sputtering
D Hydrolysis
Answer C
Which of the following is a stage of Sol gel synthesis technique of nano particles?
A Growth of particles and Agglomeration
B Condensation
C Hydrolysis
D All of these
Answer D
Synthesis of Nanomaterials, in mechanical ball milling method, size of the containers depends upon the amount
of
A Grain size
B Nature of materials
C Type of nanostructure
D None of the above
Answer A
Evaporation can be achieved by
A Resistive heating
B Laser heating
C Both Resistive heating and Laser heating
D Mechanical crushing
Answer C
In evaporation, the number of atoms leaving the surface of solid or liquid material should
A Greater than atoms returning to the surface
B less than atoms returning to the surface
C some times greater than or some times less than atoms returning to the surface
D None of these
Answer A
Sputter deposition can be carried out using
A Direct current sputtering
B Radio frequency sputtering
C Both Direct current sputtering and Radio frequency sputtering
D None of the above
Answer C
In sputter deposition method, discharge of some __________ atoms are used
A Inert gas
B Iron gas
C Carbon di oxide gas
D Hydrogen gas
Answer A
In sputter deposition method, deposition is carried out in a required ___________ obtained in a high vacuum
system
A Vapor pressure
B Atmospheric Pressure
C Gas pressure
D Both A and B
Answer C
In chemical method, synthesis of Nanomaterials occur at
A Low temperature
B High temperature
C Stellar temperature
D None of these
Answer A
In chemical method, materials are obtained in the form of ________ but can be converted into dry power or thin
films quite easily
A solid
B liquid
C gaseous
D plasma
Answer B
__________ are best synthesized using a Sol-gel method
A Argon
B Oxide ceramics
C Aluminium
D Zeolites
Answer B
The properties of nanoparticles which make them suitable for their use in space technology are,
A reduced weight
B High tensile strength
C low temperature coefficient of expansion
D All of these
Answer D
Cloths made up of nano fabrics are
Water and stain repellent
Wrinkle free
Less frequently washed
The environmental applications of nanoparticles include
A reduction in pollutants and waste
B renewable energy technologies
C detects and decomposes toxic gases and hazardous compounds
D All the above
Answer D
In the application of nanoparticles in medical science, drugs can be encapsulated in nano capsules and targeted
towards desired part of the body. This technique is known as,
A untargeted drug treatment
B Site specific drug delivery
C random drug treatment
D regular drug treatment
Answer B
Application of nano materials in electronics does not include
A Single electron transistor
B spintronics
C magnetic tunnel junctions
D smart clothes
Answer D
Nanoparticles are used in cosmetic industry as they,
A absorb ultraviolet radiation thus protecting skin
B appearance of wrinkles suppressed
C dyes and colors based on nanoparticles are harmless to the skin
D All of these
Answer D
Nanoparticles are used in textile industry as they,
A give pleasant look of synthetic fiber but comfort of cotton
B are dirt free and water repellent
C protect from germs and bacteria
D All of these
Answer D
Nanomaterials, in other words, is
A Bulk engineering
B Atomic engineering
C Small technology
D Microphysics
Answer B
Nanomaterials are being applied extensively to provide
A Drug therapy
B Diagnostics
C Tissue degeneration
D All of the above
Answer D
There is an increasing use of nanoscale particles in
A Stain resistant clothing
B Cosmetics
C Sunscreens
D All of these
Answer D
Scientists, researchers and medical personnel can ensure to do:
A Small things using the very big
B Big things using the very small
C Both of the above
D None of the above
Answer B
Nano scale magnetic materials are applied in,
A Data storage
B Cosmetics
C Construction
D None of these
Answer A
The application of Nanomaterials in the automobile industry does not include
A friction free spares
B Paining and sensors
C Long life tires with fillers
D Smart cloths
Answer D
Which device is not based on Nanomaterials?
A Single electron transistor
B Spin valves
C Transformer
D Magnetic tunnel junction
Answer C
Spin valve type devices are used in personal computer to read disk which have enabled to
A increase data storage capacity of hard disk
B decrease data storage capacity of hard disk
C both A and B
D None of these
Answer A
Very low density materials, known as
A Sol
B Gel
C Aerogel
D Both A and B
Answer C
Some special lightweight suits, jackets can be made using
A aerogels
B Sol
C Gel
D Iron
Answer A
Aerogel Material is 10 times lighter than iron
Nanocomposite of Fe2O3 and Aluminium burns much faster and is more sensitive than conventional
thermites
Germ free clothes can be obtained using __________ nanoparticles
Silver
__________ Nanoparticles of uniform size are able to absorb ultraviolet light and protect the skin
A zinc oxide and titanium oxide
B zinc chloride and titanium oxide
C titanium chloride and zinc chloride
D zinc oxide and titanium chloride
Answer A
Cloths made up of nano fabrics are
A Water and stain repellent
B Wrinkle free
C Less frequently washed
D All the above
Answer D
Which one of the following synthesis methods is superior for production of nano materials in view of purity?
A sol gel
B mechanical ball milling
C sputter deposition
D physical vapor deposition
Answer A
Which one of the following synthesis methods produces large quantity of nano materials at low cost?
A sol gel
B mechanical ball milling
C sputter deposition
D physical vapor deposition
What characteristic of sol gel technique makes it superior?
Large quantity production
Highly pure product
Production at low cost
Carbon nano tube is a cylindrical rolled up sheet of Graphene
CNT is a short form of Carbon nano tubes
Single domain nanoparticles do not show hysteresis
For increasing the performance of solar panels, which of the following nano materials are used,
Thin films quantum dots Nano tubes
Separation of carbon di oxide gas from automobile and industrial emission to reduce the green house effect is an
application of Nanomaterials in the, Environmental science
Which of the following is not the characteristic of a LASER source Divergence
What is the full form of LASER Light amplification by stimulated emission of radiation
Which of the following are the characteristics shown by laser beam
A Coherence
B High intensity
C monochromatic
D All of these
As compared Laser, ordinary light does not have
A monochromaticity
B coherence
C Large intensity
Answer All of these
Taking atoms from excited state to ground state by photon hitting the excited atom is known as, stimulated
emission
Atoms in the ground state absorb the energy photon and rose to excited state. This interaction is known as,
Absorption of radiation
The natural tendency of atoms in the excited state to release the photon and return to the ground state is
known as, spontaneous emission
Population Inversion means, More number of atoms in the excited state
The method of raising the particles from lower energy state to higher energy state so that population
inversion achieved is called,
Pumping mechanism
An energy state which has longer life time as compared to excited state is known as
Metastable state
An energy state which have highest life time and in which atoms are most stable is,
Ground state
Population inversion is completed in certain medium so that laser beam can be produced. Such a medium is
known as,
Active medium
The emission responsible for producing laser is,
Stimulated emission
Population inversion in preparing a laser beam can be achieved
when one of the excited states is more populated than the ground state
Stimulated emission process is favored whenever
Population inversion is attained
In a three level pumping mechanism, which one of the following energy state is not present? non radiative
transition state
In a three level pumping mechanism, how many energy states are present? three
In a four level pumping mechanism, how many energy states are present?
four
The laser action takes place when a transition of atoms occurs from
Metastable state to any lower energy state
In ruby laser which part acts as an active medium material
Ruby rod
Ruby laser is a Solid state laser
Ruby laser is a_ Three level laser system
In Ruby laser optical pumping is achieved by _ Xenon Flash lamp
Ruby laser is a pulsed laser source
Ruby rod is made up of Aluminum oxide Al2O3 + Chromium Oxide Cr2O3
In ruby laser, population inversion is achieved by
Optical pumping
The wavelength of the emitted light in Ruby laser is
6943 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
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 a graded index fiber, the refractive index Decreases parabolically along the radius of the core
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
(
)
All the beams entering the fiber within the acceptance angle travel along the length of fiber. The cone
formed by the range of angles within acceptance angle is called as ,
Acceptance cone
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,
)
Answer (
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
a) 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
28) The Ruby rod is surrounded by a helical Xenon flash tube
31) Population inversion occurs in non-equilibrium state
34) Transmission loss of optical fiber compared to copper wire is lower
36) Step index fiber sustains only
Single mode of propagation
Multimode of propagation
37) Compared to copper cable the information carrying capacity of optical fiber system is Superior
43) In optical fiber, ray undergoes total internal reflection only if angle of incidence is greater than
critical angle
46) In fiber optics, the signal source is Light waves.
52) The main drawback of ruby laser is that the output beam is not continuous
53) The main advantages of gas lasers are Monochromatic, pure spectrum
55) The gas laser consist of a fused Quartz tube
58) Mixture of He : Ne is filled in the tube with pressure of 1.0: 0.1 mm of Hg
59) In Gas laser tube is filled with majority of He and minority of Ne
60) In Gas laser, excited He atoms colloid with Ne atoms
61) Excited state has life time 10-8 sec
63) 10-3 sec is the life time of metastable state
64) Semiconductor diode laser have sides of the order of 1mm
65) In semiconductor diode laser thickness of the active region is 1µm
66) To achieve population inversion in a semiconductor diode, pn junction should be heavily doped
67) Laser is a device which gives output in the form of an intense, coherent and monochromatic
beam of light
71) In a p-n junction diode laser, the role of pumping agent is played by forward current
73) An optical fiber has a shape of cylindrical
75) An optical fiber consists of an inner cylinder called the core
76) In optical fiber, light carried by Core
82) 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
An echo is heard when direct and reflected sound waves reach the listener with a time interval of about
1/7 sec
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
Magnetostriction method is used when frequencies needed are 100 KHZ
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
By using ultrasonic waves, depth of the sea is equal to Vt/2
The coefficient of absorption of an open window is taken as 1
The time for which the sound persists in the hall is called as Reverberation Time
Reverberation Time is measured in B Open Window unit (OWU)
The unit of absorption coefficient is Seconds
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 correct expression for Sabine’s formula is
=
Reverberation time T can be expressed as
The Reverberation time T depends upon,
A the reflecting properties of the walls, floor and ceiling
B volume of the hall
C coefficient of absorption
D All of these
Answer D All of these
The factors which determine the acoustical quality of the hall are,
A The initial sound from the source should be of adequate intensity
B The sound should be evenly spread over the whole area covered by the audience
C The successive sounds should be clear and distinct.
D All of these
Answer D All of these
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 absorption coefficient is defined as,
A =
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 ultrasonics is above 20,000 Hz
Ultrasonic waves can be heard by bat
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 an ac voltage is applied across a quartz crystal, it vibrates at the frequency of the applied voltage.
This effect is known as,
Piezoelectric effect
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