The resistivity of potentiometer wire is $40\times {10}^{-8} \mathrm{\Omega } \mathrm{m}$ and its area of cross-section is $8\times {10}^{-6} {\mathrm{m}}^2$. If $0.2 \mathrm{A}$ current is flowing through the wire, the potential gradient of the wire is

• A

  $0.1 \mathrm{V} {\mathrm{m}}^{-1}$

   
• Correct answer
  B

  ${10}^{-2} \mathrm{V} {\mathrm{m}}^{-1}$
• C

  ${10}^{-3} \mathrm{V} {\mathrm{m}}^{-1}$
• D

  ${10}^{-4} \mathrm{V} {\mathrm{m}}^{-1}$

Hence, the correct answer is option: 'B'.