A potentiometer wire has a length of 4 m and resistance of 20 Ω. It is connected in series with resistance of 2980 Ω and a cell of emf 4 V. Calculate the potential along the wire. 

0.65 × 10^-2 V m^-1

Length of potentiometer wire l = 4m

Resistance of potentiometer wire is $ r = 20\Omega$

Resistance connected in series with potentiometer wire R = 2980$\Omega$

EMF of the cell is $\xi = 4V$

Effective resistance is $R_s = r+R = 3000\Omega$

$I = \frac{\xi}{R_s} = \frac{4}{3000} = 1.33 \times 10^{-3}A$

Potential drop across the wire is $V = IR_s = 26.6 \times 10^{-3}V$

Potential Gradient $= \frac{V}{l} = \frac{ 26.6 \times 10^{-3}}{4} = 6.65\times 10^{-3} V/m$