Discussion Forum



1)

The resistivity of potentiometer wire  is  40 x 10-8 ohm  -metre and its area of cross-section is 8 x 10-6 m2 ,If 0.2-ampere current is flowing through the wire , then the potential gradient of the wire is 


A) $10^{-1}$ V/m

B) $10^{-2}$ V/m

C) $10^{-3}$ V/m

D) $10^{-4}$ V/m

Answer:

Option B

Explanation:

Given , $\rho =40 \times 10^{-8}$ $\Omega$m

 A= $8 \times 10^{-6} m^{2}$; l= 0.2 A

 as resistance is given as R= $\frac{ \rho l}{A}$

$\therefore$    $\frac{R}{l}=\frac{\rho}{A}=\frac{40\times 10^{-8}}{8 \times 10^{-6}}=5 \times 10^{-2}$

The potential gradient of the were  is 

$\frac{V}{l}=\frac{lR}{l}=0.2\times5\times 10^{-2}= 10^{-2}  V/m$