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3. A specimen of metal has n valence electrons per m³. If v_x is the average velocity of these electrons, each having a charge e, the current density J is
Options
A. J = ne v_x
B. J = - ne v_x
C. J =
D. J =

4. A metal has a large number of free electrons. If e is electronic charge and m is mass of electron and an electric field E is applied along (say) x direction, the electrons acquire a velocity having a component v_x is x direction. Then
Options
A.
B.
C.
D.

6. The measurement of Hall coefficient of a semiconductor with one type of charge carriers gives the information about
Options
A. sign of charge carrier
B. density of charge carrier
C. both sign and density of charge carrier
D. none of the above

9. For dielectrics in alternating field, polarizability a_e is a complex quantity. The imaginary part of a_e is zero for
Options
A. ? = 0
B. ? ? ?
C. ? = 0 and ? ? ?
D. ? = natural frequency ?₀

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