You can experimentally check the Joule-Lenz law using a calorimeter filled with water, a stopwatch, a heater, a thermometer, a rheostat, an ammeter, and a voltmeter. It is necessary to connect the electric circuit and the heater to the mains and by changing the current through the heater using a rheostat, measure the water temperature in the calorimeter using a thermometer at regular intervals, measured by a stopwatch.
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