Question

The potential difference $\mathrm{V}$ across a cell of emf $\mathrm{E}$ and internal resistance $\mathrm{r}$ is ___________.

Answer 1

Electromotive force:

1. Electromotive force, often known as emf, is measured in volts.
2. The electro motive force is the potential difference between the terminals of a cell when no current is taken from it, i.e. when the cell is in an open circuit.

Factors affecting emf $\left(\mathrm{E}\right)$:

1. Material of the electrodes.
2. Electrodes that are used in the cell.

Moreover, the shape of the electrodes, the distance between them, and the amount of electrolyte used in the cell have no effect on the e.m.f of the cell, and the amount of current drawn from it has no effect on the e.m.f of the cell.

Potential Difference across a cell:

1. Let the potential difference be $\mathrm{V}$, Emf of cell be $\mathrm{E}$, current be $\mathrm{I}$ and internal resistance be $\mathrm{r}$.
2. When no current flows via an external circuit and the circuit is open, the emf (electromotive force) is the potential difference between the terminals of a battery.
3. The voltage between the terminals of the battery when the current is taken from it to an external source is known as the potential difference.
4. The potential difference across a cell will be $\mathrm{V}=\mathrm{E}-\mathrm{Ir}$.

Hence, the potential difference V across a cell of emf E and internal resistance r is $\mathbf{V}\mathbf{=}\mathbf{E}\mathbf{-}\mathit{I}\mathit{r}$.