Question

The unit of emf of a cell is:
$(A)$ Dyne
$(B)$ Volt
$(C)$ Ampere
$(D)$ Joule

Answer 1

Hint: The electromotive force is defined as the energy of the battery per coulomb’s charge passing through it. We can obtain the unit of emf of the cell from the basic expression.

Formula used:
The electromotive force expression is given by,
$E = \dfrac{W}{Q}$.
Where $W$ is the work done, $Q$ is the charge that has a unit of coulomb.

Complete answer:
First, let us discuss the term electromotive force and how the electromotive force of the cell is determined. It can be defined as the energy per unit electric charge imparted by a battery and the electric generator.
Electromotive force is produced when the energy is converted from one form to another in the battery or the generator. For example, the chemical energy in the battery is converted into electrical energy. The device will be working on the electric charge being transformed within it.
We can consider the one terminal of the device that is positively charged. The work done on a unit charge electric is gained per unit electric charge.
That is,
$E = \dfrac{W}{Q}$
Where $W$ is the work done, $Q$ is the charge that has a unit of coulomb.
From the expression, we have the work done that has a unit of Joule. The charge $Q$ has the unit of coulomb. If we substitute the units in the above expressions we get,
$ \Rightarrow E = \dfrac{{Joule}}{{Coulomb}}$
The given expression states that the joule per coulomb gives the value of volt $\left( V \right)$.
$ \Rightarrow E = \dfrac{{Joule}}{{Coulomb}}$
$ \Rightarrow E = V$
Therefore, the unit of the electromotive force is Volt $\left( V \right)$.

Hence option \[\left( B \right)\] is the correct answer.

Note: The SI unit of the emf of a cell is volt. In a centimeter gram second that is in the CGS unit system, the unit of the emf of the cell is statvolt. Stat volt can be defined as the energy per electrostatic unit of charge.