Plot a graph showing the variation of current density (J) versus the electric field ( E ) For two conductors of different materials. What information from this plot regarding the properties of the conducting material, can be obtained which can be used to select suitable materials for use in making (i ) standard resistance and (ii) connecting wires in electric circuit?

Explanation

We know that `J = sigma E` or `sigma = J//E`
where `sigma` is the electrical condutivity of the conductor.
The variation of current density ( J) versus the electric field (E ) for two conductors A and B is shown in figure.
Here, the slope of each st. line tells the conductivity of that material.
From graph, `sigma_(B) gt sigma_(A)`.
We know that electrical resistivity (`rho)` is reciprocal of electrical conductivity.
`:. rho_(A)/rho_(B) = sigma_(B)/sigma_(A) gt 1 or rho_(A) gt rho_(B)`
The material to be used in making a standard resistance, we require that the resistance of the given conducting wire is large. It will be so if its resistivity is large and its conductivity is small. Therefore, the material A is used in making the standard resistance.
The material to be used in making a connecting wire, we require that the resistance of the given connecting wire is small. It will be so if its resistivity is small and the conductivity is large. Therefore the material B is used in making a connecting wire is the circuit.