Q. When a material becomes a superconductor, its resistivity becomes

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Q. In a piezoelectric crystal, the application of mechanical force will cause

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Q. Consider the following statement:

If an electric field is applied to an n type semiconductor bar, the electrons and holes move in opposite directions due to their opposite charges. The net currents is
1. both due to electrons and holes with electrons as majority carriers
2. sum of hole and electron currents
3. difference between electron and hole currents.

Which of above statements are correct?

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Q. As the temperature of a pure silicon specimen is increased

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Q. Assertion (A): In many materials, dielectric polarization causes mechanical distortion.
Reason (R): If dielectric polarization causes mechanical distortion then mechanical distortion must cause dielectric polarization.

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Q. Semi conducting materials are all

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Q. Silicon and germanium atoms combine orderly into array of atoms located in repetitive geometric pattern. This pattern is called

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Q. In a pure sample of silicon

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Q. Orbital magnetic dipole moment is due to the motion of electron in its orbit around nucleus.

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Q. 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 = Ɛ₀ƐᵣA/d .

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Q. Assertion (A): An electron having charge - e and mass m and lying in an electric field E is subjected to an acceleration - (e/m) E.

Reason (R): If there are n electrons/m³ moving with velocity vᵪ and each electron has a charge - e, the current density J = - n evᵪ.

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Q. When a pentavalent impurity is added, the semiconductor becomes

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Q. In body centred cubic structure, comers and centre of the cube are occupied by identical atoms.

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Q. For a multiplate capacitor having n plates, A as area of each plate, the capacitance is proportional to

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Q. The orientation polarization is

1. directly proportional to temperature
2. inversely proportional to temperature
3. inversely proportional to square of permanent dipole moment
4. directly proportional to square of permanent dipole moment.

Which of the above are correct?

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Q. The relaxation time of electrons in a metal is of the order of

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Q. Assertion (A): For elemental dielectrics, P = NaeEi where N is number of atoms/m³, P is polarization, ae is electronic polarization and Ei is internal electric field.

Reason (R): In elemental dielectrics there are no permanent dipoles or ions.

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Q. The circumference of an electron orbit is equal to integer times the wavelength of electron.

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Q. In a specimen of silicon steel, a field strength of 200 A/m causes a flux density of 0.5 T. In a specimen of cast iron, the same H would cause B to be

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Q. In a rare gas, the molecules of some atoms have an excess positive or negative charge. The electric field tends to shift positive ions relative to negative ions. This is known as ionic polarization.

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