[tex]dane:\\t = 30 \ min = 30\cdot60 \ s = 1 \ 800 \ s\\U = 230 \ V\\I = 4 \ A\\1 \ kWh = 3 \ 600 \ 000 \ J\\szukane:\\W = ?\\\\Rozwiazanie\\\\W = U\cdot I\cdot t\\\\W = 230 \ V\cdot 4 \ A \cdot 1800 \ s=1 \ 656 \ 000 \ J\\\\W = \frac{1656000 \ J}{3600000\frac{J}{kWh}} = 0,46 \ kWh\\\\Odp. \ W = 0,46[/tex]
