Question

How does a potentiometer measure EMF?

Answer 1

Potentiometers

1. Potentiometers work on the premise that the potential difference between two spots on a wire with the same cross-sectional area is inversely proportional to the distance of the wire between the points.
2. By balancing the length of a potentiometer, we can find the emf of a cell. Here, the emf of the cell is equal to the fall of the potentiometer along the length of the potentiometer wire.
3. By finding the equilibrium length, we can use a potentiometer to calculate the emf of the cell. Since no current is being drawn from the cell, the drop in potential along the length of the wire is equal to the emf of the cell.

Terms: $G$refers to the Galvanometer, and $A$refers to Ammeter.

The Formula for Calculating the EMF:

1. EMF is calculated using two primary formulae. The quantity of joules that each coulomb of charge absorbs while moving through the cell is the basic definition.

$\epsilon =\frac{E}{Q}$, where $\epsilon =$Electromotive force, $E=$The energy in the circuit, $Q=$Charge of the circuit.

2. If we are aware of the energy produced and the quantity of charge moving through the cell. It is the easiest method for determining the EMF.

Instead, we may define it more along the lines of Ohm's law, i.e.$V=IR$. The formula is thus: $\epsilon =I(R+r)$

Where, $I=$Current, $\epsilon =$The electromotive force of cell, $R=$Resistance in the circuit, $r=$Internal resistance of a cell, $V=$Voltage.

Now, expanding this:

$$\begin{gathered} \epsilon =IR+Ir \\ \epsilon =V+Ir \end{gathered}$$
This demonstrates that the voltage between the terminals, the current flowing, and the internal resistance of the cell can all be used to determine the EMF.