(a) When 1 joule of work is done in carrying 1 coulomb of charge , from infinity to a point in the electric field, then potential at that point is called 1 volt. (b) Potential difference , V = Work done on unit charge = W/q Work is 100\\ J , q = 20\\ C Potential difference , V = W/q = 100/20 = 5\\ V