Question

State the relationship between emf and terminal voltage of a cell.

Answer 1

According to the law of conservation of energy, the total work done W in moving a charge Q through the complete circuit is equal to the sum of the work done W' in the external circuit and the work done ω inside the electrolyte of the cell. This can be expressed as:

W = W' + ω

By dividing this entire equation by the charge Q on both sides, we get:

`W/Q = (W')/Q + ω/Q`

From the core definitions of electrical terms, we know that the work done per unit charge represents different potentials:

`W/Q` = ε (Electromotive force), `(W')/Q` = V (Terminal voltage), `ω/Q` = v (Internal voltage)

Substituting these terms into the expression gives:

ε = V + v

or v = ε − V

This clearly shows that whenever a current flows from a cell, the terminal voltage V measured across its leads drops below the actual electromotive force ε by an amount equal to the internal voltage loss v within the cell itself.