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Materials and Components

31.

The classes of solid dielectrics are

Answer: C

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32.

Assertion (A): In a perfect capacitor, the current density is given by ω ∈0E0∈'rcos(ωt + 90°), where ∈r' is real part of dielectric constant.

Reason (R): In a perfect capacitor, dielectric losses are zero.

Answer: A

If dielectric losses are zero, the current in capacitor leads the applied voltage by 90°.

Also imaginary part of is ∈r is zero.

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Answer: B

Ferroelectric materials have permanent polarization.

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Answer: B

Atomic number is not dependent on lattice structure.

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35.

Inductors used at V.H.F. are made using

Answer: D

Thin film technique ensure low hysteresis and eddy current losses.

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36.

For a photoconductor with equal electron and hole mobilities and perfect ohmic contacts at the ends, an increase in intensity of optical illumination results in

Answer: C

It is the characteristic of a photoconductor that its resistance decreases with increase in illumination.

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37.

Resistivity of rubber is about

Answer: D

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38.

In metals the valence electron wave functions are strongly perturbed by the presence of neighbouring atoms.

Answer: A

In a metal valence electrons are shared by all atoms.

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39.

Diamond is a paramagnetic material.

Answer: B

Diamond is diamagnetic.

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40.

Assertion (A): When an electron is revolving in its orbit and magnetic field is also present, the angular frequency of electron will be affected by the magnetic field.

Reason (R): In the case of electron revolving in its orbit in the presence of magnetic field, the orbital magnetic dipole moment is not affected by the presence of magnetic field.

Answer: C

Orbital magnetic moment is equal to (-e/2m).

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