The unit of e.m.f. of a cell is:
A. dyne
B. volt
C. ampere
D. joule

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Hint: If we look at what is emf i.e., electromotive force, it is defined as a battery’s energy per coulomb of charge passing through it. So we will obtain the unit of emf from the basic expression. EMF of a cell could be measured by a voltmeter and it is the voltage across the cell. Electromotive force is given by the expression$E=\dfrac{W}{Q}$.

Complete step by step answer:
Let us first discuss what electro-motive force is and who the electromotive force of a cell is determined. It is the energy per unit electric charge imparted by an electric generator or a battery.
EMF is produced as the energy is converted from one form to another in a generator or a battery (for example chemical energy in a battery is transformed into electric energy) as the device does work on the electric charge being transformed within it.
Now one terminal of the device becomes positively charged. The work done on a unit of electric charge gained per unit electric charge.
i.e., $E=\dfrac{W}{Q}$
Here, W is work done which is having the unit joule (J) and Q is the charge having the unit coulomb. So, the unit of emf could be derived as joules per coulomb. This is also known as volt.
So the SI unit of emf is volt V.

Therefore, the correct answer is option B.


Note:
The S.I. unit of electromotive force is found as volt (V). Volt can be defined as one joule per coulomb of electric charge. In the CGS system, the unit of emf is statvolt which can be defined as one erg per electrostatic unit (stat) of charge.