Question

Лед массой 2 кг, находящийся при температуре плавления, растапливают на электроплитке. В электроплитке две спирали сопротивлением 20 Омкаждая соединены последовательно и включены в сеть 220 В. Весь лед растаял за 12 мин. Определите КПД процесса. С ПОЛНЫМ ОБЬЯСНЕНИЕМ И НАПИШИТЕ КАКИЕ ТЕМЫ НУЖНО ЗНАТЬ ЧТОБЫ РЕШАТЬ ЗАДАЧИ ПОДОБНОГО ТИПА

Answer 1

КПД = (Аполезная÷Азатраченная)×100%.
А полезная = теплоте плавления льда, то есть массе льда, умноженной на удельную теплоту плавления льда λ = 3,3×10⁵ Дж/Кг
Таким образом, Аполезная равна 6,6×10⁵ Дж.
Затраченная работа будет равна (по закону Джоуля-Ленца).
A =(U²×t)/R = (220)²×720÷40 = 871200 Дж = 8,712×10⁵ Дж.
КПД = (6,6/8,712)×100% ≈ 75,7%

Знать нужно основы термодинамики и молекулярной физики. И ещё тему "Работа тока".

Ответ: КПД равен 75,7%

Answer 2

To determine the efficiency of the process, we need to calculate the amount of energy supplied to the system and the amount of energy used to melt the ice. The efficiency (η) of a process is defined as the ratio of useful output energy to the input energy.

Calculation of Input Energy:

The input energy is the electrical energy supplied to the system. We can calculate it using the formula:

Input Energy (E_in) = Power (P) × Time (t)

The power can be calculated using Ohm's law:

Power (P) = (Voltage (V))^2 / Resistance (R)

In this case, the voltage is 220 V and the resistance is the sum of the resistances of the two heating elements, which is 20 Ω each. Therefore, the total resistance (R) is 40 Ω.

Substituting the values into the formula, we get:

Power (P) = (220 V)^2 / 40 Ω

Now, we can calculate the input energy by multiplying the power by the time, which is 12 minutes (converted to seconds):

Input Energy (E_in) = Power (P) × Time (t)

Calculation of Output Energy:

The output energy is the energy required to melt the ice. To calculate it, we need to know the heat of fusion of ice, which is the amount of energy required to change 1 kg of ice at its melting point to 1 kg of water at the same temperature. The heat of fusion of ice is approximately 334,000 J/kg.

Since the mass of the ice is given as 2 kg, the output energy can be calculated as:

Output Energy (E_out) = Mass (m) × Heat of Fusion (H)

Substituting the values, we get:

Output Energy (E_out) = 2 kg × 334,000 J/kg

Calculation of Efficiency:

The efficiency (η) of the process is given by the formula:

Efficiency (η) = Output Energy (E_out) / Input Energy (E_in)

Substituting the values, we can calculate the efficiency of the process.

Now, let's summarize the calculations and determine the efficiency of the process:

- Input Energy (E_in) = (220 V)^2 / 40 Ω × 12 minutes (converted to seconds) - Output Energy (E_out) = 2 kg × 334,000 J/kg - Efficiency (η) = Output Energy (E_out) / Input Energy (E_in)

Please note that to solve similar problems, you need to have a good understanding of electrical circuits, Ohm's law, power calculations, and the concept of efficiency. Additionally, knowledge of thermodynamics, specifically the heat of fusion of ice, is required to calculate the output energy.