Question

What is the difference between terminal voltage and e.m.f?

Answer 1

Definition

1. The electric potential generated by such an electrochemical cell either through varying the magnetic field is called electromagnetic force (e.m.f).
2. The force exerted by the power source of such an electrical circuit to move charged electrons through a conductive path, allowing them to do work such as lighting a lamp is called voltage.

The difference between terminal voltage and e.m.f

E.M.F	Terminal Voltage
1.When no current would be pulled from a cell, the potential difference between its endpoints has been referred to as the electro-motive force of the cell (or e.m.f.).	1.Whenever current is extracted from a cell, this same potential difference seen between the cell's electrodes has been referred to as the terminal voltage.
2.E.m.f is measured by the potentiometer.	2.Terminal voltage is measured by a voltmeter.
3.Formula: $\mathrm{\epsilon }=\mathrm{I}(\mathrm{R}+\mathrm{r})$ Here, R is the external resistance, and r is the internal resistance.	3.Formula: $\mathrm{V}=\mathrm{IR}$ Here, I is the current and R is the external resistance.
4.Intensity is always constant.	4.Because of the voltage drop throughout the external resistance, the intensity will fluctuate.
5.It is induced in electric, gravitational, and magnetic fields.	5.It is induced only in the gravitational field.

Therefore, throughout the absence of electric current, the voltage created between two terminals of a source is e.m.f, and the potential difference that develops between the two electrode potentials of a source is a terminal voltage.