define 1 volt

A volt is a joule per coulomb.If you're struggling to remember try and picture the situation. Imagine current as individual units of charge passing through a battery. The charge has passed round the whole circuit and 'given' its energy to the components in the circuit by the time it reaches the battery so it needs to get some more. One volt from the battery gives this individual charge unit some energy. The unit of energy is joules and unit of charge is coulomb hence 1 volt is one joule (energy) per charge (coulomb).