1Which of the following defines the Dielectric Constant () of a material?
A.The ratio of electric field in vacuum to electric field in the material
B.The ratio of electric flux density to electric field intensity
C.The product of permittivity of free space and electric field
D.The ratio of polarization to electric field
Correct Answer: The ratio of electric field in vacuum to electric field in the material
Explanation:The dielectric constant ( or ) is defined as the ratio of the permittivity of the substance to the permittivity of free space, which is equivalent to the ratio of the electric field in a vacuum to the electric field inside the dielectric material.
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2What happens to the electric field intensity inside a dielectric material when it is placed in an external electric field?
A.It increases
B.It decreases
C.It remains zero
D.It remains unchanged
Correct Answer: It decreases
Explanation:When a dielectric is placed in an external electric field, polarization occurs. An internal electric field is induced in the opposite direction, which reduces the net electric field intensity inside the material.
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3The relationship between electric flux density (), electric field (), and polarization () is given by:
A.
B.
C.
D.
Correct Answer:
Explanation:The total electric flux density inside a dielectric is the sum of the contribution from the external field () and the polarization of the material ().
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4Which type of polarization depends strongly on temperature?
A.Electronic Polarization
B.Ionic Polarization
C.Orientational Polarization
D.Space Charge Polarization
Correct Answer: Orientational Polarization
Explanation:Orientational polarization involves the alignment of permanent dipoles. Thermal energy tends to randomize this alignment; therefore, it is strongly temperature-dependent, usually inversely proportional to temperature.
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5The phenomenon where an electric potential difference is generated across a material in response to applied mechanical stress is known as:
A.Inverse Piezoelectric Effect
B.Direct Piezoelectric Effect
C.Magnetostriction
D.Electrostriction
Correct Answer: Direct Piezoelectric Effect
Explanation:The Direct Piezoelectric Effect is the generation of an electric charge or potential difference in response to applied mechanical stress.
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6Which of the following materials is a common piezoelectric material?
A.Silicon
B.Quartz
C.Copper
D.Germanium
Correct Answer: Quartz
Explanation:Quartz () is a naturally occurring crystal that exhibits piezoelectric properties due to its non-centrosymmetric crystal structure.
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7The Inverse Piezoelectric Effect is utilized in which of the following applications?
A.Production of ultrasonic waves
B.Detection of ultrasonic waves
C.Microphones
D.Pressure sensors
Correct Answer: Production of ultrasonic waves
Explanation:The inverse piezoelectric effect involves changing the dimensions of a material by applying an electric field. If an alternating electric field is applied, the crystal vibrates, which is used to produce ultrasonic waves.
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8For a material to exhibit the piezoelectric effect, its crystal structure must lack:
A.Periodicity
B.Center of inversion (Centrosymmetry)
C.Grain boundaries
D.Dislocations
Correct Answer: Center of inversion (Centrosymmetry)
Explanation:Piezoelectricity occurs only in crystals that have no center of symmetry (non-centrosymmetric). If a center of inversion exists, the stress does not result in net polarization.
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9In the detection of ultrasonic waves using the piezoelectric detector, the principle used is:
A.Direct Piezoelectric Effect
B.Inverse Piezoelectric Effect
C.Magnetostriction
D.Hall Effect
Correct Answer: Direct Piezoelectric Effect
Explanation:When ultrasonic waves hit a piezoelectric crystal, they cause mechanical stress. The direct piezoelectric effect converts this stress into an electrical signal, allowing for detection.
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10Magnetic susceptibility () for a diamagnetic material is:
A.Small and positive
B.Large and positive
C.Small and negative
D.Large and negative
Correct Answer: Small and negative
Explanation:Diamagnetic materials repel magnetic fields slightly, resulting in a magnetic susceptibility that is small and negative (independent of temperature).
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11Which material class has permanent magnetic dipoles that are randomly oriented in the absence of an external field?
A.Diamagnetic
B.Paramagnetic
C.Superconducting
D.Dielectric
Correct Answer: Paramagnetic
Explanation:Paramagnetic materials possess permanent magnetic dipoles. In the absence of an external field, thermal agitation randomizes their orientation, resulting in zero net magnetization.
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12Above the Curie temperature, a ferromagnetic material becomes:
A.Diamagnetic
B.Paramagnetic
C.Superconducting
D.Antiferromagnetic
Correct Answer: Paramagnetic
Explanation:The Curie temperature is the critical point above which the thermal energy disrupts the magnetic domain alignment of a ferromagnetic material, turning it into a paramagnet.
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13The area of the B-H hysteresis loop represents:
A.Magnetic permeability
B.Susceptibility
C.Energy loss per cycle per unit volume
D.Retentivity
Correct Answer: Energy loss per cycle per unit volume
Explanation:The area enclosed by the hysteresis loop represents the energy dissipated as heat during a complete cycle of magnetization and demagnetization (hysteresis loss).
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14Hard magnetic materials used for permanent magnets and data storage are characterized by:
A.Low retentivity and low coercivity
B.High retentivity and high coercivity
C.High permeability and low hysteresis loss
D.Zero coercivity
Correct Answer: High retentivity and high coercivity
Explanation:Hard magnetic materials need to retain magnetism (high retentivity) and resist demagnetization (high coercivity), making them suitable for permanent magnets and storage devices.
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15In magnetic data storage (e.g., Hard Drives), data is stored in the form of:
A.Electric charges
B.Magnetic domains
C.Phonons
D.Light pulses
Correct Answer: Magnetic domains
Explanation:Magnetic storage devices record data by magnetizing tiny sections of the material (domains) in specific directions to represent binary bits (0 and 1).
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16The fundamental property of a superconductor is:
A.Zero electrical resistance
B.Zero magnetic permeability
C.Both A and B
D.Infinite conductivity and high resistance
Correct Answer: Both A and B
Explanation:Superconductors are characterized by two fundamental properties below the critical temperature: zero electrical resistance (infinite conductivity) and the Meissner effect (perfect diamagnetism/zero permeability inside).
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17The temperature at which a material transitions from a normal state to a superconducting state is called:
A.Curie Temperature
B.Neel Temperature
C.Critical Temperature ()
D.Debye Temperature
Correct Answer: Critical Temperature ()
Explanation:The Critical Temperature () is the specific temperature below which a material loses all electrical resistance and becomes a superconductor.
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18The expulsion of magnetic flux lines from the interior of a superconductor when it is cooled below is known as:
A.Josephson Effect
B.Meissner Effect
C.Peltier Effect
D.Seebeck Effect
Correct Answer: Meissner Effect
Explanation:The Meissner Effect is the expulsion of a magnetic field from a superconductor during its transition to the superconducting state, making it a perfect diamagnet.
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19According to the Meissner effect, the magnetic susceptibility () of a superconductor is:
A.
B.1
C.-1
D.Infinity
Correct Answer: -1
Explanation:Since inside a superconductor, . Susceptibility .
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20Type I superconductors are also known as:
A.Hard superconductors
B.Soft superconductors
C.High temperature superconductors
D.Ceramic superconductors
Correct Answer: Soft superconductors
Explanation:Type I superconductors are called soft superconductors because they lose their superconductivity abruptly at a relatively low critical magnetic field.
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21Which of the following is a characteristic of Type II superconductors?
A.They exhibit a complete Meissner effect up to a very high field
B.They have only one critical magnetic field
C.They allow partial penetration of magnetic field between and
D.They are usually pure metals
Correct Answer: They allow partial penetration of magnetic field between and
Explanation:Type II superconductors have two critical fields, and . Between these fields, they exist in a mixed or vortex state where magnetic flux partially penetrates the material.
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22According to BCS theory, superconductivity is caused by the formation of:
A.Electron-Hole pairs
B.Cooper pairs
C.Magnetic dipoles
D.Polarons
Correct Answer: Cooper pairs
Explanation:The BCS (Bardeen-Cooper-Schrieffer) theory explains that superconductivity arises from the pairing of electrons, known as Cooper pairs, mediated by lattice vibrations (phonons).
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23The interaction mediating the formation of Cooper pairs in conventional superconductors is:
A.Electron-Electron Coulomb repulsion
B.Electron-Phonon interaction
C.Electron-Photon interaction
D.Spin-Spin coupling
Correct Answer: Electron-Phonon interaction
Explanation:In BCS theory, an electron distorts the lattice (creating a phonon), and this distortion attracts a second electron, overcoming the Coulomb repulsion to form a bound pair.
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24The critical magnetic field varies with temperature according to the relation:
A.
B.
C.
D.
Correct Answer:
Explanation:The critical magnetic field decreases parabolically as temperature increases, reaching zero at the critical temperature .
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25Nanomaterials are typically defined as materials having at least one dimension in the range of:
A.1 to 100 micrometers
B.1 to 100 nanometers
C.1 to 100 angstroms
D.1 to 100 millimeters
Correct Answer: 1 to 100 nanometers
Explanation:Nanomaterials are defined by having structural features or at least one dimension in the range of 1 nm to 100 nm.
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26As the size of a material reduces to the nanoscale, the surface area to volume ratio:
A.Decreases significantly
B.Remains constant
C.Increases significantly
D.Becomes zero
Correct Answer: Increases significantly
Explanation:One of the defining characteristics of nanomaterials is a very high surface-area-to-volume ratio, which greatly influences their reactivity and physical properties.
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27Quantum Dots are an example of which type of nanomaterial?
A.0-Dimensional (0D)
B.1-Dimensional (1D)
C.2-Dimensional (2D)
D.3-Dimensional (3D)
Correct Answer: 0-Dimensional (0D)
Explanation:Quantum dots are confined in all three spatial dimensions, essentially reducing them to a point, hence they are classified as 0-Dimensional nanomaterials.
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28Carbon Nanotubes (CNTs) are best described as:
A.Sheets of graphene rolled into a cylinder
B.Spherical fullerene balls
C.Diamond-like cubic structures
D.Amorphous carbon clusters
Correct Answer: Sheets of graphene rolled into a cylinder
Explanation:A Carbon Nanotube can be visualized as a single sheet of graphene (a 2D hexagonal lattice of carbon) rolled into a seamless cylinder.
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29The phenomenon where the band gap of a semiconductor increases as the particle size decreases is known as:
A.Surface Plasmon Resonance
B.Quantum Confinement Effect
C.Meissner Effect
D.Photoelectric Effect
Correct Answer: Quantum Confinement Effect
Explanation:Quantum confinement occurs when the particle size is comparable to the de Broglie wavelength of the electron, leading to discrete energy levels and a widening of the band gap.
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30Which of the following is a 'Bottom-Up' approach for synthesizing nanomaterials?
A.Ball Milling
B.Sol-Gel process
C.Lithography
D.Etching
Correct Answer: Sol-Gel process
Explanation:Bottom-up approaches build materials atom-by-atom or molecule-by-molecule. The Sol-Gel process creates networks from chemical solutions (monomers) to form larger structures.
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31Graphene consists of:
A.A single layer of carbon atoms in a hexagonal lattice
B.A multi-layer structure of silicon
C.A spherical cage of 60 carbon atoms
D.A linear chain of carbon atoms
Correct Answer: A single layer of carbon atoms in a hexagonal lattice
Explanation:Graphene is a 2D allotrope of carbon consisting of a single layer of atoms arranged in a honeycomb (hexagonal) lattice.
Correct Answer: Detection of extremely weak magnetic fields
Explanation:SQUIDs are very sensitive magnetometers used to measure extremely subtle magnetic fields, widely used in medical imaging (MEG) and geology.
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33High-temperature superconductors are typically:
A.Pure metals like Mercury
B.Alloys like Nb-Ti
C.Ceramic oxides (Perovskites)
D.Polymers
Correct Answer: Ceramic oxides (Perovskites)
Explanation:High- superconductors, discovered in the late 1980s, are generally ceramic copper oxide materials (like YBCO) with complex crystal structures.
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34The dielectric strength of a material refers to:
A.The maximum current it can conduct
B.The maximum electric field it can withstand without breakdown
C.Its ability to store magnetic energy
D.Its mechanical tensile strength
Correct Answer: The maximum electric field it can withstand without breakdown
Explanation:Dielectric strength is the maximum electric field intensity a dielectric material can endure before it loses its insulating properties and electrical breakdown occurs.
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35Clausius-Mosotti relation connects:
A.Dielectric constant and magnetic susceptibility
B.Macroscopic dielectric constant and microscopic polarizability
C.Stress and Strain in piezoelectrics
D.Critical temperature and Magnetic field
Correct Answer: Macroscopic dielectric constant and microscopic polarizability
Explanation:The Clausius-Mosotti equation relates the macroscopic property (dielectric constant) of a symmetric dielectric material to the microscopic property (polarizability of atoms/molecules).
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36Ferromagnetic materials show a hysteresis loop. The value of magnetic field required to reduce the residual magnetism () to zero is called:
A.Retentivity
B.Saturation
C.Coercivity
D.Permeability
Correct Answer: Coercivity
Explanation:Coercivity is the intensity of the applied magnetic field required to reduce the magnetization of a material to zero after the magnetization of the sample has been driven to saturation.
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37Which of the following is NOT a property of nanomaterials compared to their bulk counterparts?
A.Lower melting point
B.Changed optical properties (color)
C.Identical electronic band structure
D.Enhanced mechanical strength
Correct Answer: Identical electronic band structure
Explanation:Nanomaterials have distinct electronic band structures (discretization of energy levels) compared to bulk materials due to quantum confinement; they are not identical.
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38What is the primary mechanism of heat loss in a transformer core?
A.Dielectric loss
B.Hysteresis loss and Eddy currents
C.Superconducting loss
D.Piezoelectric vibration
Correct Answer: Hysteresis loss and Eddy currents
Explanation:Transformer cores are magnetic materials subjected to alternating fields. Energy is lost due to the hysteresis loop area and circulating eddy currents.
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39A material used for making a permanent magnet should have:
A.High retentivity, High coercivity
B.Low retentivity, Low coercivity
C.High retentivity, Low coercivity
D.Low retentivity, High coercivity
Correct Answer: High retentivity, High coercivity
Explanation:Permanent magnets must retain strong magnetism (High Retentivity) and resist being demagnetized by stray fields (High Coercivity).
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40The energy gap () in a superconductor at K is related to the critical temperature () in BCS theory roughly by:
A.
B.
C.
D.
Correct Answer:
Explanation:BCS theory predicts an energy gap at absolute zero of approximately , which separates the superconducting ground state from excited states.
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41Which material is typically used for magnetic data storage in hard disks?
A.Soft Iron
B.Cobalt-Platinum-Chromium alloy
C.Silicon
D.Lead
Correct Answer: Cobalt-Platinum-Chromium alloy
Explanation:Hard disk platters require a material with high coercivity and granularity to store bits reliably. Co-Pt-Cr alloys are commonly used.
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42What is the effect of a DC electric field on the resonance frequency of a piezoelectric crystal?
A.It has no effect
B.It changes the physical dimensions, potentially altering resonance
C.It melts the crystal
D.It makes the crystal magnetic
Correct Answer: It changes the physical dimensions, potentially altering resonance
Explanation:Applying a DC field causes static deformation (inverse piezo effect), which changes the dimensions and can fine-tune or shift the resonance frequency.
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43The penetration depth () in a superconductor is the depth at which the external magnetic field decays to:
A.Zero
B. times its surface value
C.Half its surface value
D.Infinite
Correct Answer: times its surface value
Explanation:The London penetration depth is the distance into the superconductor where the magnetic field decays exponentially to (approx 37%) of its value at the surface.
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44Which of the following describes the 'Isotope Effect' in superconductors?
A.
B.
C.
D. is independent of Mass
Correct Answer:
Explanation:The Isotope Effect states that the critical temperature is inversely proportional to the square root of the isotopic mass (), supporting the phonon-mediated mechanism of BCS theory.
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45Gold nanoparticles appear red or purple in solution instead of gold due to:
A.Rusting
B.Surface Plasmon Resonance (SPR)
C.Nuclear fission
D.Dye impurities
Correct Answer: Surface Plasmon Resonance (SPR)
Explanation:At the nanoscale, the oscillation of conduction electrons on the surface of gold nanoparticles resonates with specific wavelengths of light (SPR), absorbing green/blue and reflecting red/purple.
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46PZT (Lead Zirconate Titanate) is a famous example of:
A.Superconducting material
B.Ferroelectric/Piezoelectric material
C.Diamagnetic material
D.Nanomaterial
Correct Answer: Ferroelectric/Piezoelectric material
Explanation:PZT is a ceramic perovskite material that shows a strong piezoelectric effect and is widely used in sensors and actuators.
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47Electronic polarization occurs due to:
A.Displacement of positive and negative ions
B.Displacement of the electron cloud relative to the nucleus
C.Alignment of permanent dipoles
D.Accumulation of charges at interfaces
Correct Answer: Displacement of the electron cloud relative to the nucleus
Explanation:Electronic polarization is the displacement of the center of the negative electron cloud relative to the center of the positive nucleus in an atom under an electric field.
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48Maglev trains utilize which property of superconductors?
A.Zero resistance for power transmission
B.Magnetic Levitation via Meissner Effect
C.Thermal insulation
D.Piezoelectric vibration
Correct Answer: Magnetic Levitation via Meissner Effect
Explanation:Maglev (Magnetic Levitation) trains use the strong repulsion generated by the Meissner effect (or magnetic flux pinning in Type II) to float the train above the tracks.
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49A nanowire is an example of:
A.0D nanomaterial
B.1D nanomaterial
C.2D nanomaterial
D.Bulk material
Correct Answer: 1D nanomaterial
Explanation:A nanowire has confinement in two dimensions (diameter is nanoscale), leaving electrons free to move in only one dimension (length). Hence, it is a 1D nanomaterial.
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50The unit of Dipole Moment is:
A.Coulomb / meter
B.Coulomb-meter ()
C.Farad / meter
D.Volt / meter
Correct Answer: Coulomb-meter ()
Explanation:Electric dipole moment , where is charge (Coulombs) and is distance (meters). The unit is Coulomb-meter.
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