Which of the following statements is not correct about cell potential ?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → Measured when current is flowing
The cell potential is the potential difference between the two electrodes of a galvanic cell, i.e. the difference between the reduction potentials of the cathode and the anode:
\( \displaystyle E_{\mathrm{cell}} = E_{\mathrm{right}} - E_{\mathrm{left}} = E_{\mathrm{cathode}} - E_{\mathrm{anode}} \)
When a current is drawn, part of this potential is lost inside the cell, so the reading falls. The cell potential is therefore taken as the emf, the value when no current is drawn through the cell, and it is measured with a potentiometer, which balances the cell so that no current flows. So “Measured when current is flowing” is not correct.
Option (1) Difference in the electrode potential — Correct about cell potential. Ecell = Ecathode − Eanode.
Option (2) Measured by potentiometer — Correct about cell potential. A potentiometer measures the potential with no current drawn, i.e. the emf.
Option (3) Cell potential depends on temperature — Correct about cell potential. The Nernst equation, Ecell = E°cell − (2.303RT/nF) log Q, contains T.
Option (4) Measured when current is flowing — Not correct about cell potential. The emf is the value when no current is drawn.
NCERT (2026-27 edition):
Galvanic Cells – “… The potential difference between the two electrodes of a galvanic cell is called the cell potential and is measured in volts. The cell potential is the difference between the electrode potentials (reduction potentials) of the cathode and anode. It is called the cell electromotive force (emf) of the cell when no current is drawn through the cell.”