Сопротивление константанового провода 2.5 ом, площадь поперечного сечения 2мм2.какова длина провода?

l=2.5*2/0,5=10 мм

ответ: 10мм

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Η=  * 100 %  a полезная = (c₁+c₂)mδt  c₁ - удельная теплоёмкость воды ( 4200 дж/кг*с ) c₂ - удельная теплоёмкость чайника ( 100 дж/кг * с ) m - масса ( 3 кг ) δt - разности температур ( 100 с - 10 с = 90 с ) а полезная = (4200+100) * 3 * 90 = 4300 * 3 * 90 = 1161000 дж а затраченная = q*m  q - удельная теплота сгорания ( 36000000 дж/кг ) m - масса  m = p * v  p - плотность газа ( 1,25 кг/м³ ) v - объём ( 60 л = 0,06 м³ ) m = 1,25 * 0,06 = 0,075 кг  а полезная = 36000000 * 0,075 = 2700000 дж  η =  = 0,43 * 100 = 43 %