An electric heater brings 10 kg of water to a boil in 7 minutes, the initial temperature of which is 20 degrees Celsius

An electric heater brings 10 kg of water to a boil in 7 minutes, the initial temperature of which is 20 degrees Celsius. What is the current in its heating element if the voltage is 220 V? Heater efficiency is 90%.

m = 10 kg.

Efficiency = 90%.

U = 220 V.

T = 7 min = 420 s.

t1 = 20 ° C.

t2 = 100 ° C.

С = 4200 J / kg * ° C.

I -?

The efficiency coefficient shows what part of the consumed energy Ezat as a percentage goes into the useful Epol: Efficiency = Epol * 100% / Ezat, where Epol is the amount of heat that went to heating the water, Ezat is the amount of heat that is released in the heater.

Epol = C * m * (t2 – t1).

Ezat = I * U * T.

Efficiency = C * m * (t2 – t1) * 100% / I * U * T.

The magnitude of the current I will be determined by the formula: I = C * m * (t2 – t1) * 100% / efficiency * U * T.

I = 4200 J / kg * ° C * 10 kg * (100 ° C – 20 ° C) * 100% / 90% * 220 V * 420 s = 40.4 A.

Answer: in the heating element, the current strength is I = 40.4 A.