Question

by what other name is the unit joule/ coulomb called ?

Answer 1

Potential energy of a charge system :  U = q V  = work done in bringing a charge q from infinity to to a point with potential V. 
So  Joule = Coulomb * Volt        J/C = Volt

Answer 2

Answer:

The other name of joule/coulomb is called volt.

Explanation:

Energy has unit Joule. By the definition, Power is rate at which energy is transformed. As the unit of Power which is Watt, W = Joule/Second.  

Therefore Joule = Watt x Second

But we know that, Power = Voltage x Current

Therefore Joule = Voltage x Ampere x Second --(1)

Moreover, rate of change of charge is current. Therefore Ampere = Coulomb/Second

So Coulomb = Ampere x Second --(2)

Substituting (2) into (1),

Joule = Voltage x Coulomb.  

Therefore Joule/Coulomb = Voltage

Hence the other name of Joule/Coulomb is Volt.