Materials And Components MCQs
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A 200 turn coil has a self inductance of 10 mH. If the number of turns is doubled, all other quantities remaining the same, the self inductance will be
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A. 2.5 mH
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B. 5 mH
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C. 20 mH
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D. 40 mH
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Correct Answer: Option D
A capacitor can be represented by a capacitance and resistance in parallel. For a good capacitor, this parallel resistance should be
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A. negligible
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B. low
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C. high
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D. very high
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Correct Answer: Option D
A circular sphere mile is the area of cross-section of a wire
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A. having a diameter equal to 1 miles
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B. having a radius equal to 1 miles
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C. having a circumference equal to 1 miles
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D. none of the above
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Correct Answer: Option A
A conductor carries 10 A current in + x direction and is lying in a field having a flux density 0.2 T directed along + z direction. The magnitude of force per metre length and direction are
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A. 2 N, + y direction
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B. 2 N, - y direction
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C. 0.02 N, + y direction
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D. 0.02 N, - y direction
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Correct Answer: Option B
A copper atom is neutral. Its core has a net charge of
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B. + 1
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C. - 1
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D. + 2
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Correct Answer: Option B
A copper specimen has resistivity equal to 1.8 x 10-8 ohm-m at room temperature. At a temperature of 700 K, the resistivity is likely to be
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A. 1.6 x 10-8 Ω-m
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B. 2 x 10-8 Ω-m
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C. 3 x 10-8 Ω-m
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D. 6 x 10-8 Ω-m
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Correct Answer: Option D
A dielectric is subjected to alternating field. The dielectric losses are potential to
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A. real part of dielectric constant
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B. imaginary part of dielectric constant
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C. both real and imaginary parts of dielectric constant
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D. either real or imaginary part of dielectric constant
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Correct Answer: Option B
A dielectric material must be
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A. insulator
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B. good conductor
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C. resistor
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D. semiconductor
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Correct Answer: Option A
A dielectric of relative permittivity ∈r is subjected to a homogeneous electric field E. The dipole moment P per unit volume is given by
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A. P = constant
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B. P = ∈0 E
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C. P = ∈0(∈r - 1) E
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D. P = ∈r E
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Correct Answer: Option C
A good dielectric should have
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A. low losses
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B. good heat conductivity
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C. high intrinsic strength
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D. all of the above
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Correct Answer: Option D
A liquid has N permanent dipoles μp per unit volume and has been subjected to dc field for a long time such that orientation polarization is P0. At t = 0, the field is suddenly removed, then polarization
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A. will remain constant at P0
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B. will become zero at t = 0
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C. will delay to zero with a time constant
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D. either b or c
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Correct Answer: Option C
A magnet does not attract
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A. nickel
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B. iron
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C. copper
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D. iron and copper
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Correct Answer: Option C
A magnetic field exists around
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A. moving charges
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B. static charges
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C. iron
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D. copper
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Correct Answer: Option A
A material which is lightly repelled by a magnetic field is known as
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A. diamagnetic material
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B. non-magnetic material
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C. ferromagnetic material
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D. paramagnetic material
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Correct Answer: Option A
A parallel plate capacitor having C = 200 x 10-12 F has loss dielectric having tan δ = 4 x 10-4. At an ac voltage of f = 106 Hz and peak value 2 V, the dielectric losses are
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A. 10-8 W
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B. 10-6 W
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C. 10-4 W
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D. 10-2 W
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Correct Answer: Option B
A permeable substance is one
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A. which is strong magnet
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B. which is a weak magnet
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C. which is a good conductor
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D. through which magnetic lines of force can pass easily
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Correct Answer: Option D
A photoconductor is a
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A. conductor
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B. semiconductor
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C. insulator
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D. superconductor
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Correct Answer: Option B
A piece of copper and another piece of Germanium are cooled from 30°C to 80 K. The resistance of
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A. copper decreases and germanium increases
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B. both decreases
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C. both increases
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D. copper increases and germanium decreases
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Correct Answer: Option A
A piece of iron is placed in a magnetic field
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A. the magnetic field will not be affected
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B. the magnetic lines of force will bend to pass through the piece
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C. the magnetic lines of force will bend away from the piece
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D. any of the above depending on type of iron
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Correct Answer: Option B
A rare gas has N atoms per m3. If electronic polarizability of single atom of this gas is ae, then
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A. ∈r = Ne
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B. ∈0∈r = Ne
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C. ∈0(∈r - 1) = Ne
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D. ∈0(∈r - 2) = Ne
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Correct Answer: Option C
A sample of N type semiconductor has an electron density of 6.25 x 1018/cm3 at 300 K. If intrinsic concentration of carriers in this sample is 2.5 x 1013/cm3 at this temperature, the hole density is
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A. 106 / cm3
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B. 108 / cm3
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C. 1010 / cm3
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D. 1012 / cm3
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Correct Answer: Option B
A sheet of bakelite is inserted between the plates of an air capacitor. The capacitance will
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A. increase
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B. decrease
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C. remain the same
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D. may increase or decrease
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Correct Answer: Option A
A single layer air cored coil has n turns and inductance L. If a new coil is formed by having 2n turns while keeping the coil length and diameter the same, the new inductance is
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A. 0.5 L
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B. L
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C. 2 L
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D. 4 L
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Correct Answer: Option D
A wire is carrying current I. The field intensity H at a distance r from the wire
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A. is directed towards wire
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B. is directed away from wire
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C. is tangential every where to a circle of radius r
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D. none of the above
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Correct Answer: Option C
Above a certain temperature, the specific heat of a metal becomes constant. This temperature is called
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A. Debye temperature
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B. Curie temperature
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C. Neel temperature
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D. Transition temperature
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Correct Answer: Option A
An atom of a rare gas is placed is an electric field E. Then
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A. the nucleus will be shifted in the direction of E by an amount which is proportional to E.
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B. the nucleus will not be shifted.
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C. the nucleus will be shifted in the direction of E by an amount which is independent of E.
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D. the nucleus will be shifted in a direction opposite to that of E.
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Correct Answer: Option A
An electrolytic capacitor can be used for
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A. ac only
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B. dc only
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C. both ac and dc
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D. high frequency ac
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Correct Answer: Option B
An electron (charge -e) is rotating in a circular orbit of radius R, around a proton with charge +e at a constant angular velocity ω. The orbital magnetic dipole moment is
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A. 0.5 eω R2
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B. eω R2
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C. 2 eω R2
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D. 0.5 eω R3
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Correct Answer: Option A
An electron in a homogeneous magnetic field and having velocity perpendicular to the direction of field moves
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A. perpendicular to the field
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B. along the field
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C. along a straight line inclined at 45° to field
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D. in a circular path
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Correct Answer: Option D
An electron shell corresponding to principal quantum number n can contain a maximum of
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A. n2 electrons
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B. 2n2 electrons
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C. 2n electron
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D. n3 electron
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Correct Answer: Option B
An iron specimen has µr = 1000 when B = 0.3 T. If B = 0.35 T, µr
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A. will be 1000
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B. will be less than 1000
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C. will be more than 1000
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D. may be more or less than 1000
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Correct Answer: Option D
As per Matthiessen’s rule, the total resistivity r of a conductor can be written as r = ri + aT, where ri and a are constants and T is absolute temperature. At very low temperatures
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A. aT = 0
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B. aT > i
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C. aT ∼ i
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D. aT < i
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Correct Answer: Option D
As per temperature limits, the number of categories of solid dielectrics are
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A. 7
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B. 6
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C. 8
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D. 5
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Correct Answer: Option A
As regards ∈0 and ∈r (absolute and relative permittivity)
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A. both ∈0 and ∈r can be interpreted in terms of atomic properties of medium
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B. only ∈r can be interpreted in terms of atomic properties of medium
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C. only ∈0 can be interpreted in terms of atomic properties
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D. ∈r has no physical significance
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Correct Answer: Option B
As regards dielectric constant εr
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A. the units are farads/m
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B. the units are newton/coulomb
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C. it is dimensionless
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D. the units are farads
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Correct Answer: Option C
As regards ferromagnetic Curie temperature Qf and paramagnetic curie temperature θ
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A. Qf > θ
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B. θ > Qf
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C. θ equal to or less than Qf
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D. θ may be equal to less than or more Qf
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Correct Answer: Option B
As the atoms of rare gases become larger, electronic polarizability
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A. increases
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B. decreases
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C. remains the same
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D. may increase or decrease
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Correct Answer: Option C
As the temperature of a pure silicon specimen is increased
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A. the number of free electrons increases
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B. the number of holes decreases
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C. the number of holes increases
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D. the number of free electrons and holes increases
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Correct Answer: Option D
As the temperature of semiconductor is increased
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A. the average number of free charge carriers decreases
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B. the average number of free charge carriers increases
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C. the average number of free charge carriers remains the same
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D. the average number of free charge carriers may increase or decrease
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Correct Answer: Option B
As the viscosity of a liquid increases, the relaxation time
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A. remains constant
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B. increases
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C. decreases
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D. first decreases then increases
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Correct Answer: Option B