Вопрос школьника по предмету Физика
Нагревательный элемент кофеварки имеет две секции сопротивлением 25 Ом каждая. Объем кофеварки 2л. Начальная температура воды 20 градусов Цельсия, напряжение сети 120 В, КПД нагревателя 80%. Определить через сколько времени закипит вода,если 1) включена одна секция 2) включены обе секции последовательно 3) включены обе секции параллельно
Ответ учителя по предмету Физика
mводы=2 кг; Q=cm(t2-t1);Q=4200*2*(100-20)=672000 Дж;
1) Qтока=U^2*t*0.8/R;Qтока=Qводы; t=QR/(U^2*0.8); t=672000*25/(120^2*0.8)=1458 с=24 мин
2)R1=2R;t=QR/(U^2*0.8); t=672000*50/(120^2*0.8)=2916 с=48.6 мин
3) t=R1=R/2; t=QR/(U^2*0.8); t=672*12.5/(120^2*0.8)=729 с=12 мин
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