An elementary book on electricity and magnetism and their applications . heat rapidly by radiationinto the air. A thermometer isimmersed in the liquid to determineits rise of temperature due to theheat given it from the wire. Theamount of heat which is required toraise the temperature of a gram ofwater one degree centigrade is calleda calorie. The number of caloriesgiven by the wire to the water inthe calorimeter is determined fromthe amount of water and its risein temperature, proper correctionsbeing made for the effect of thevessel. The experiments of Joule,of Rowland (an American scientist)
An elementary book on electricity and magnetism and their applications . heat rapidly by radiationinto the air. A thermometer isimmersed in the liquid to determineits rise of temperature due to theheat given it from the wire. Theamount of heat which is required toraise the temperature of a gram ofwater one degree centigrade is calleda calorie. The number of caloriesgiven by the wire to the water inthe calorimeter is determined fromthe amount of water and its risein temperature, proper correctionsbeing made for the effect of thevessel. The experiments of Joule,of Rowland (an American scientist), and of others, have shownthat the work represented by one joule (watt second) is equiva-lent to the heat represented by practically of a , the total number of calories of heat produced, in onesecond by the current passing through the wire in a calorimeter isequal to PR. The total heat produced in the calorimeterin any time is also equal to ] PR multiplied by the numberof seconds in the time. This may be written in the followingform:. Coil of Resistance Wire Fig. 36. —Simple form of elec-tric calorimeter. ELECTRIC POWER AND HEATING EFFECTS 77 H = PRtwhen H= Heat in calories, /= Current in amperes,R = Resistance in ohms, f = Time in seconds. This experimental fact, or law of nature, is sometimes calledJoules Law. By determining the total heat produced in the calorimeterin a fixed time when the current is passed through a wire ofknown resistance, the value of the current may be computed. It will be seen from what precedes that one ampere flowingthrough a resistance of one ohm expends continuously a powerof one watt (which is equivalent to the expenditure of one jouleof work every second), and that it will raise one gram of ° C- every second. In steam engineering the unit of heat is the British ThermalUnit (), which is defined as the amount of heat requiredto raise 1 pound of water 1° Fahrenheit. It can be shown that 1
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmagnetism, bookyear19
