Question

Define 'current density'. Is it a scalar or a vector ? An electric field E is maintained in a metallic conductor. If n be the number of electrons (mass m, charge – e) per unit volume in the conductor and τ its relaxation time, show that the current density j = αE, where α = (ne²/m)τ.

What is a Wheatstone bridge ? Obtain the necessary conditions under which the Wheatstone bridge is balanced.

Electrons drift with speed vd in a conductor with potential difference V across its ends. If V is reduced to V/2, their drift speed will become :

Define resistivity of a conductor. How does the resistivity of a conductor depend upon the following : (a) Number density of free electrons in the conductor (n) (b) Their relaxation time (τ)