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When the electric current is too small, the voltage of cell is given as

E=E (cathode)-E(anode)

E( cathode) is electrode's potential which is attached to the negative terminal of the current source.

E (anode) is electrode's potential which is attached to the positive terminal of the current source.

Overpotential:The activation energy of a reaction at an electrode can be overcome by voltage. The required voltage to apply is called overpotential.

Ohmic potential:In an electrochemical cell, the electrical resistance of a solution while current I flows can be overcome by voltage. The required voltage to apply is called ohmic potential.

${\mathrm{E}}_{\mathrm{ohmic}}=\mathrm{IR}$

Concentration Polarization: It is the change in concentration of products and reactants at electrode's surface unlike they are same in solution.

Given,

The concentration of${\mathrm{I}}^{-}$ is 0.01 M.

E( anode$)0.535-\frac{0.05916}{2}\log \frac{0.{01}^3}{0.0003}=0.608\mathrm{V}$

E=E( cathode ) -E( anode )IR-overpoetentials

$$\begin{gathered} =-0.591\mathrm{V}-0.608\mathrm{V}-(2.0\mathrm{惟})(0.063\mathrm{A})-0.382\mathrm{V}-0.025\mathrm{V} \\ =-1.732\mathrm{V} \end{gathered}$$

In order to drive the electrolysis of ${\mathrm{I}}^{-}$to role="math" localid="1663645612720" ${\mathrm{I}}_3^{-},-1.732\mathrm{V}$is required.