The resistivity of a potentiometer wire is `40xx10^(-8)Omega-m` and its area of cross section is `8xx10^(-6)m^(2)`. If 0.2 A current is flowing through the wire the potential gradient will be
A. `10^(-2)` volt/m
B. `10^(-1)` volt/m
C. `3.2 xx 10^(-2)` vol/m
D. 1 vol/m