A student passes different steady currents through a metallic specimen and measures the corresponding internal electric field E for each current density J. The plot of E versus J is a straight line through the origin.
(i) Explain, on the basis of basic definitions, why the E–J graph is linear for a metallic conductor at constant temperature.
(ii) Show that the numerical value of the slope of this straight line represents the resistivity of the material.
(iii) The measured slope is 4.0×10−8VsC−1m. State the physical quantity this value corresponds to and write its SI unit clearly.