Question

Определить сопротивление электрического чайника с КПД 80% если 2 кг воды с начальной температурой 20С нагревается до кипения через 8 мин.При напряжении 220В.прошу помогите,меня не было на этой теме а задали решать((

Answer 1

Количество теплоты необходимое для нагрева: Q=cm(t2-t1)=672 КДж
Так как КПД чайника 80% ему надо будет выделить 840 КДж
Закон Джоуля-Ленца гласит, что Q=I^2Rt=IUt. Выразим из этой формулы силу тока: I=Q/Ut=840000/(220*8*60)=7.95 А.
Далее из закона Ома выражаем сопротивление: R=U/I=220/7.95=27.7 Ом.

Answer 2

Calculation of the Resistance of an Electric Kettle

To determine the resistance of an electric kettle, we need to use the formula:

Resistance (R) = Voltage (V) / Current (I)

In this case, we are given the following information: - Voltage (V) = 220V - Power Efficiency (η) = 80% (or 0.8) - Mass of water (m) = 2 kg - Initial temperature of water (T1) = 20°C - Time taken to heat the water (t) = 8 minutes

To calculate the resistance, we need to find the current (I) flowing through the kettle. We can use the power equation:

Power (P) = Voltage (V) * Current (I)

The power can be calculated using the energy equation:

Energy (E) = Mass (m) * Specific Heat Capacity (c) * Change in Temperature (ΔT)

The specific heat capacity of water is approximately 4.18 J/g°C, and the change in temperature is the difference between the final temperature (100°C) and the initial temperature (20°C).

Let's calculate the resistance step by step:

1. Calculate the energy required to heat the water: - Specific Heat Capacity (c) = 4.18 J/g°C - Change in Temperature (ΔT) = 100°C - 20°C = 80°C - Energy (E) = Mass (m) * Specific Heat Capacity (c) * Change in Temperature (ΔT)

2. Calculate the power: - Power (P) = Energy (E) / Time (t)

3. Calculate the current: - Current (I) = Power (P) / Voltage (V)

4. Calculate the resistance: - Resistance (R) = Voltage (V) / Current (I)

Let's perform the calculations:

1. Calculate the energy required to heat the water: - Specific Heat Capacity (c) = 4.18 J/g°C - Change in Temperature (ΔT) = 80°C - Mass (m) = 2 kg - Energy (E) = Mass (m) * Specific Heat Capacity (c) * Change in Temperature (ΔT)

Energy (E) = 2 kg * 4.18 J/g°C * 80°C = 668.8 kJ

2. Calculate the power: - Time (t) = 8 minutes = 8 * 60 seconds - Power (P) = Energy (E) / Time (t)

Power (P) = 668.8 kJ / (8 * 60 s) = 1.394 kJ/s = 1.394 kW

3. Calculate the current: - Voltage (V) = 220V - Current (I) = Power (P) / Voltage (V)

Current (I) = 1.394 kW / 220V = 6.336 A

4. Calculate the resistance: - Resistance (R) = Voltage (V) / Current (I)

Resistance (R) = 220V / 6.336 A = 34.7 Ω

Therefore, the resistance of the electric kettle is approximately 34.7 Ω.

Please note that the above calculations assume ideal conditions and do not take into account any other factors that may affect the resistance of the electric kettle.