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

Answer 1

Теплота,  поглощенная льдом, может быть рассчитана как удельная теплота плавления льда помноженная на массу льда.
Q1=335000*2 = 670000 Дж
Теплота, которую отдала спираль равна U^2/(R)*t
Q2 = 220^2/40*720 = 871200 Дж
КПД посчитаем как теплоту поглощенную, отнесенную к теплоте выделенной
670000/871200 = 0.77 или 77%

Answer 2

Calculating the Efficiency of the Melting Process

To calculate the efficiency of the melting process, we can use the formula:

Efficiency = (Useful energy output / Total energy input) x 100%

First, we need to determine the useful energy output and the total energy input for the melting process.

Useful Energy Output

The useful energy output in this case is the energy required to melt the ice. This can be calculated using the formula:

Energy = mass x specific heat capacity x temperature change

Given: - Mass of ice (m) = 2 kg - Specific heat capacity of ice (c) = 334 J/kg°C (at 0°C, the temperature of melting ice)

The energy required to melt the ice can be calculated using the formula: Energy = mass x specific heat capacity x temperature change Energy = 2 kg x 334 J/kg°C x 0°C Energy = 668 J

Total Energy Input

The total energy input is the electrical energy supplied to the heating elements in the electric stove. This can be calculated using the formula:

Energy = power x time

Given: - Resistance of each heating element (R) = 20 Ω - Voltage of the power supply (V) = 220 V - Time taken for the ice to melt = 12 minutes = 720 seconds

The power (P) can be calculated using the formula: Power = (Voltage^2) / Resistance Power = (220 V)^2 / 20 Ω Power = 2420 W

The total energy input can be calculated using the formula: Energy = power x time Energy = 2420 W x 720 s Energy = 1,742,400 J

Calculating Efficiency

Now that we have the useful energy output and the total energy input, we can calculate the efficiency using the formula:

Efficiency = (Useful energy output / Total energy input) x 100% Efficiency = (668 J / 1,742,400 J) x 100% Efficiency ≈ 0.0383%

Therefore, the efficiency of the melting process is approximately 0.0383%.