ELEMENTS OF ELECTRICITY AND MAGNETISM. 



41. A fine copper wire wound in one layer upon a pane of glass 

 is submerged in an oil-bath and a measured current / is allowed 

 to flow through the wire causing the temperature of the bath to 

 rise slowly. A voltmeter is connected across the terminals of the 

 coil of copper wire and simultaneous readings of current / in 

 the coil, electromotive force E across the terminals of the coil 

 and temperature T of the bath were taken as follows : 



Calculate the resistance of the wire at each observed temperature, 

 and plot a curve of which the abscissas represent observed tem- 

 peratures and of which the ordinates represent the calculated 

 values of the resistance of the wire. 



42. An electrolytic cell, consisting of a one per cent, solution 

 of sulphuric acid between lead electrodes, was connected to 

 supply mains, and the following values of current / flowing 

 through the cell, electromotive force E between the electrodes, 

 and temperature T of the solution were observed. Calculate 

 the resistance of the cell at each temperature, and plot a curve 

 of which the abscissas represent temperatures, and of which the 

 ordinates represent the corresponding calculated resistances of 

 the cell. 



Note. The resistance of the cell in this problem is to be calculated by means of 

 Ohm's Law. Ohm's Law, however, is not strictly applicable in this case, because a 

 portion of the work which is done on the cell is used to produce chemical action, 

 whereas Ohm's Law is true only in case all the work delivered to a circuit is spent in 



