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ECE :: Materials and Components

  1. The core of a solenoid is made of material of relative permeability μr. A small cavity area dA and length dl is cut in the core. If it is desired that flux density in the cavity should be equal to B0

  2. A.
    the fields inside and outside the cavity must be equal
    B.
    the field inside the cavity must be made stronger than field outside the cavity
    C.
    the field inside the cavity must be made weaker than the field outside the cavity
    D.
    none of the above

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  3. A copper specimen has resistivity equal to 1.8 x 10-8 ohm-m at room temperature. At a temperature of 700 K, the resistivity is likely to be

  4. A.
    1.6 x 10-8 Ω-m
    B.
    2 x 10-8 Ω-m
    C.
    3 x 10-8 Ω-m
    D.
    6 x 10-8 Ω-m

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  5. Assertion (A): Dielectric constant is independent of temperature unless the temperature is extremely high.

    Reason (R): For normal temperatures the number of atoms per unit volume is constant.

  6. A.
    Both A and R are true and R is correct explanation of A
    B.
    Both A and R are true but R is not correct explanation of A
    C.
    A is true but R is false
    D.
    A is false but R is true

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  7. As the atoms of rare gases become larger, electronic polarizability

  8. A.
    increases
    B.
    decreases
    C.
    remains the same
    D.
    may increase or decrease

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  9. Ferrimagnetic materials have anti-parallel orientation of equal moments of permanent dipoles.

  10. A.
    True
    B.
    False

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  11. Yettrium-iron garnet (Y2Fe5O12) is a soft magnetic material suitable for applications involving

  12. A.
    dc
    B.
    50 Hz ac
    C.
    ac of a few K Hz
    D.
    ac of a few hundred MHz

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  13. The mass of proton and electron are

  14. A.
    1.672 x 10-26 kg and 9.107 x 10-31 kg respectively
    B.
    9.107 x 10-26 kg and 9.107 x 10-31 kg respectively
    C.
    9.107 x 10-29 kg and 9.107 x 10-31 kg respectively
    D.
    9.107 x 10-30 kg and 9.107 x 10-31 kg respectively

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  15. A rare gas having N atoms/m3 is subjected to an electric field E. The electric dipole moment per unit volume is proportional to N and E.

  16. A.
    True
    B.
    False

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  17. In an intrinsic semiconductor, at a given temperature T

  18. A.
    the number of electrons-hole pairs generated per second due to thermal motion are equal to the number of electron-hole pairs lost per second due to recombination
    B.
    the number of electron-hole pairs generated per second due to thermal motion is always less than the number of electron-hole pairs lost per second due to recombination
    C.
    the number of electron hole pairs generated per second due to thermal motion is always more than the number of electron-hole pairs lost per second due to recombination
    D.
    any of the above

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