Determine the efficiency of an electric soldering iron with a resistance of 25 Ohm if the copper part of it weighing 0.2 kg heats up to 60 ° C in 4 minutes. The current in the spiral of the soldering iron is 4 A.
Initial data: R (resistance of the electric soldering iron taken) = 25 Ohm; m (mass of the copper part of the soldering iron) = 0.2 kg; Δt (temperature change of the soldering iron during operation) = 600 ºС; t (soldering iron operating time) = 4 min (240 s); I (current in the soldering iron spiral) = 4 A.
Constants: Cm (specific heat of copper) = 400 J / (kg * ºС).
The efficiency of the soldering iron is determined by the formula: η = Cm * m * Δt / (I ^ 2 * R * t).
Calculation: η = 400 * 0.2 * 600 / (4 ^ 2 * 25 * 240) = 0.5 (50%).
Answer: An electric soldering iron has an efficiency of 50%.
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