[tex]Dane:\\U = 220 \ V\\I = 0,5 \ A\\t = 20 \ min = 20\cdot60 \ s = 1 \ 200 \ s\\k = 0,63 \ zl \ za \ 1kWh\\1 \ kWh = 3 \ 600 \ 000 \ J\\szukane:\\a) \ W = ?\\b) \ K = ?\\\\Rozwiazanie\\\\a)\\W = U\cdot I\cdot t\\\\W = 220 \ V\cdot0,5 \ A\cdot1200 \ s=132 \ 000 \ J\\\\W = \frac{132000 \ J}{3600000\frac{J}{kWh}} = 0,03(6) \ kWh \approx0,0367 \ kWh\\\\b)\\K = W\cdot k\\\\K = 0,0367 \ kWh\cdot0,63\frac{zl}{kWh} = 0,02 \ zl[/tex]
