[tex]dane:\\q = 4 \ C\\W = 12 \ J\\szukane:\\U = ?\\\\W = U\cdot I\cdot t\\\\ale \ \ q = I\cdot t, \ zatem:\\\\W = U\cdot q \ \ /:q\\\\U = \frac{W}{q}\\\\U = \frac{12 \ J}{4 \ C}\\\\\underline{U = 3 \ V}[/tex]
