400. There are four contributors to total polarization of a material. These contributions are electronic, ionic, dipolar and space-charge polarization. At optical frequencies the only major contribution to polarization is from
A. electronic polarization
B. ionic polarization
C. dipolar polarization
D. space-charge polarization

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401.  For electrons and holes, the Hall I +Er coefficients are
A. both positive
B. both negative
C. positive and negative, respectively
D. negative and positive, respectively

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402. In semiconductor wafer cleaning, trichloroethylene is used to remove
A. Dust particles from the surface
B. Grease from the surface
C. Impurities from within the crystal
D. Moisture from the surface

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403.  Consider the following statements about ferrites :1. Ferrites have high resistivity.2. Ferrites have low eddy current losses.3. Ferrites are used as core materials in high frequency (MHz) transformers. Which of the statements given above are correct?
A. 1, 2 and 3
B. 1 and 2
C. 1 and 3
D. 2 and 3

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404. Anecessary but not a sufficient condition for a crystal to show ferro-electricity is
A. absence of centre of symmetry
B. presence of centre of symmetry
C. presence of both translational and rotational symmetry
D. absence of both translational and rotational symmetry

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405.  In a dielectric material there are four contributions to the total polarisation. Out of these only one is dependent on temperature and this contribution is
A. electric polarization
B. space-charge polarization
C. ionic polarization
D. orientational polarisation

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406.  If m = permanent dipole moment, k = Boltzmann constant and T= absolute temperature, then orientational polarisability is equal to
A.3kT
B.3kT
C. 3kTm
D. 3kTm2

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