Q. In metals the thermal conductivity K and electrical conductivity σ are related as (K/σT) = L, L is known as

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Q. Assertion (A): If WF is Fermi energy, v is velocity of electron and m is mass of electron, then 1/2mv² = WF .
Reason (R): Conductivity of a metal depends on temperature and impurity concentration.

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Q. Dielectric constant of transformer oil is about

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Q. 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.

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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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