Materials and Components
Assertion (A): In imperfect capacitors, the current does not lead the applied ac voltage by 90°.
Reason (R): When subjected to ac fields, the dielectric constant can be expressed as ∈'r - j∈"r.
Answer: A
Imaginary part of ∈r gives rise to absorption of energy by the material from alternating field.
Hence current does not lead the voltage by 90°.
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Assertion (A): Copper is a monoatomic solid.
Reason (R): In a metal the valence electrons belong to all atoms.
Answer: B
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Permeability is analogous to
Answer: C
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The class of insulation of impregnated paper is
Answer: A
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The resistivity of intrinsic semiconductors, at room temperature, is of the order of
Answer: A
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A parallel plate capacitor has its length, width and separation doubled. It fringing effects are neglected, to keep the capacitance same, the dielectric constant must be
Answer: A
. When dimensions are changed, A become four times and d becomes twice.
Since ∈0 is constant, ∈r must be halved to keep C constant.
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Assertion (A): Relaxation time and mean time between collisions are equal when scattering is isotropic.
Reason (R): Mean free path of an electron λ, velocity of electron v and mean time between collisions tc are related as λ = vTc.
Answer: B
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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
Answer: C
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Assertion (A): ∈r can be determined experimentally by measuring the capacitance of a parallel plate capacitor with and without the dielectric.
Reason (R): Capacitance of a parallel plate capacitor = 
.
Answer: A
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The relationship of hysteresis loss to maximum flux density was first determined by
Answer: A
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